Spring Retry提供了自动重新调用失败的操作的功能。这在错误可能是暂时的（例如瞬时网络故障）的情况下很有用。 从2.2.0版本开始，重试功能已从Spring Batch中撤出，成为一个独立的新库：Spring Retry
<dependency> <groupId>org.springframework.retry</groupId> <artifactId>spring-retry</artifactId> </dependency> <!-- also need to add Spring AOP into our project--> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-aspects</artifactId> </dependency> 在启动类中使用@EnableRetry注解
package org.example; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.retry.annotation.EnableRetry; @SpringBootApplication @EnableRetry public class RetryApp { public static void main(String[] args) { SpringApplication.run(RetryApp.class, args); } } @Retryable需要在重试的代码中加入重试注解@Retryable
package org.example; import lombok.extern.slf4j.Slf4j; import org.springframework.retry.annotation.Backoff; import org.springframework.retry.annotation.Recover; import org.springframework.retry.annotation.Retryable; import org.springframework.stereotype.Service; import java.time.LocalDateTime; @Service @Slf4j public class RetryService { @Retryable(value = IllegalAccessException.class) public void service1() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException("manual exception"); } } 默认情况下，会重试3次，间隔1秒
我们可以从注解@Retryable中看到
@Target({ ElementType.METHOD, ElementType.TYPE }) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface Retryable { /** * Retry interceptor bean name to be applied for retryable method. Is mutually * exclusive with other attributes. * @return the retry interceptor bean name */ String interceptor() default ""; /** * Exception types that are retryable. Synonym for includes(). Defaults to empty (and * if excludes is also empty all exceptions are retried). * @return exception types to retry */ Class<? extends Throwable>[] value() default {}; /** * Exception types that are retryable. Defaults to empty (and if excludes is also * empty all exceptions are retried). * @return exception types to retry */ Class<? extends Throwable>[] include() default {}; /** * Exception types that are not retryable. Defaults to empty (and if includes is also * empty all exceptions are retried). * If includes is empty but excludes is not, all not excluded exceptions are retried * @return exception types not to retry */ Class<? extends Throwable>[] exclude() default {}; /** * A unique label for statistics reporting. If not provided the caller may choose to * ignore it, or provide a default. * * @return the label for the statistics */ String label() default ""; /** * Flag to say that the retry is stateful: i.e. exceptions are re-thrown, but the * retry policy is applied with the same policy to subsequent invocations with the * same arguments. If false then retryable exceptions are not re-thrown. * @return true if retry is stateful, default false */ boolean stateful() default false; /** * @return the maximum number of attempts (including the first failure), defaults to 3 */ int maxAttempts() default 3; //默认重试次数3次 /** * @return an expression evaluated to the maximum number of attempts (including the first failure), defaults to 3 * Overrides {@link #maxAttempts()}. * @since 1.2 */ String maxAttemptsExpression() default ""; /** * Specify the backoff properties for retrying this operation. The default is a * simple {@link Backoff} specification with no properties - see it's documentation * for defaults. * @return a backoff specification */ Backoff backoff() default @Backoff(); //默认的重试中的退避策略 /** * Specify an expression to be evaluated after the {@code SimpleRetryPolicy.canRetry()} * returns true - can be used to conditionally suppress the retry. Only invoked after * an exception is thrown. The root object for the evaluation is the last {@code Throwable}. * Other beans in the context can be referenced. * For example: * <pre class=code> * {@code "message.contains('you can retry this')"}. * </pre> * and * <pre class=code> * {@code "@someBean.shouldRetry(#root)"}. * </pre> * @return the expression. * @since 1.2 */ String exceptionExpression() default ""; /** * Bean names of retry listeners to use instead of default ones defined in Spring context * @return retry listeners bean names */ String[] listeners() default {}; } @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface Backoff { /** * Synonym for {@link #delay()}. * * @return the delay in milliseconds (default 1000) */ long value() default 1000; //默认的重试间隔1秒 /** * A canonical backoff period. Used as an initial value in the exponential case, and * as a minimum value in the uniform case. * @return the initial or canonical backoff period in milliseconds (default 1000) */ long delay() default 0; /** * The maximimum wait (in milliseconds) between retries. If less than the * {@link #delay()} then the default of * {@value org.springframework.retry.backoff.ExponentialBackOffPolicy#DEFAULT_MAX_INTERVAL} * is applied. * * @return the maximum delay between retries (default 0 = ignored) */ long maxDelay() default 0; /** * If positive, then used as a multiplier for generating the next delay for backoff. * * @return a multiplier to use to calculate the next backoff delay (default 0 = * ignored) */ double multiplier() default 0; /** * An expression evaluating to the canonical backoff period. Used as an initial value * in the exponential case, and as a minimum value in the uniform case. Overrides * {@link #delay()}. * @return the initial or canonical backoff period in milliseconds. * @since 1.2 */ String delayExpression() default ""; /** * An expression evaluating to the maximimum wait (in milliseconds) between retries. * If less than the {@link #delay()} then the default of * {@value org.springframework.retry.backoff.ExponentialBackOffPolicy#DEFAULT_MAX_INTERVAL} * is applied. Overrides {@link #maxDelay()} * * @return the maximum delay between retries (default 0 = ignored) * @since 1.2 */ String maxDelayExpression() default ""; /** * Evaluates to a vaule used as a multiplier for generating the next delay for * backoff. Overrides {@link #multiplier()}. * * @return a multiplier expression to use to calculate the next backoff delay (default * 0 = ignored) * @since 1.2 */ String multiplierExpression() default ""; /** * In the exponential case ({@link #multiplier()} > 0) set this to true to have the * backoff delays randomized, so that the maximum delay is multiplier times the * previous delay and the distribution is uniform between the two values. * * @return the flag to signal randomization is required (default false) */ boolean random() default false; } 我们来运行测试代码
package org.example; import org.junit.jupiter.api.Test; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.context.SpringBootTest; @SpringBootTest class RetryServiceTest { @Autowired private RetryService retryService; @Test void testService1() throws IllegalAccessException { retryService.service1(); } } 运行结果如下：
2021-01-05 19:40:41.221 INFO 3548 --- [ main] org.example.RetryService : do something... 2021-01-05T19:40:41.221763300 2021-01-05 19:40:42.224 INFO 3548 --- [ main] org.example.RetryService : do something... 2021-01-05T19:40:42.224436500 2021-01-05 19:40:43.225 INFO 3548 --- [ main] org.example.RetryService : do something... 2021-01-05T19:40:43.225189300 java.lang.IllegalAccessException: manual exception at org.example.RetryService.service1(RetryService.java:19) at org.example.RetryService$$FastClassBySpringCGLIB$$c0995ddb.invoke(<generated>) at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:769) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747) at org.springframework.retry.interceptor.RetryOperationsInterceptor$1.doWithRetry(RetryOperationsInterceptor.java:91) at org.springframework.retry.support.RetryTemplate.doExecute(RetryTemplate.java:287) at org.springframework.retry.support.RetryTemplate.execute(RetryTemplate.java:164) at org.springframework.retry.interceptor.RetryOperationsInterceptor.invoke(RetryOperationsInterceptor.java:118) at org.springframework.retry.annotation.AnnotationAwareRetryOperationsInterceptor.invoke(AnnotationAwareRetryOperationsInterceptor.java:153) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747) at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:689) at org.example.RetryService$$EnhancerBySpringCGLIB$$499afa1d.service1(<generated>) at org.example.RetryServiceTest.testService1(RetryServiceTest.java:16) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:566) at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:675) at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60) at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:125) at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:132) at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:124) at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:74) at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115) at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105) at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:104) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:62) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:43) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:35) at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104) at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:202) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:198) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:69) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32) at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:229) at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:197) at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:211) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:191) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128) at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71) at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33) at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220) at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53) 可以看到重新执行了3次service1()方法，然后间隔是1秒，然后最后还是重试失败，所以抛出了异常
既然我们看到了注解@Retryable中有这么多参数可以设置，那我们就来介绍几个常用的配置。
@Retryable(include = IllegalAccessException.class, maxAttempts = 5) public void service2() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException("manual exception"); } 首先是maxAttempts，用于设置重试次数
2021-01-06 09:30:11.263 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:11.263621900 2021-01-06 09:30:12.265 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:12.265629100 2021-01-06 09:30:13.265 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:13.265701 2021-01-06 09:30:14.266 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:14.266705400 2021-01-06 09:30:15.266 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:15.266733200 java.lang.IllegalAccessException: manual exception .... 从运行结果可以看到，方法执行了5次。
下面来介绍maxAttemptsExpression的设置
@Retryable(value = IllegalAccessException.class, maxAttemptsExpression = "${maxAttempts}") public void service3() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException("manual exception"); } maxAttemptsExpression则可以使用表达式，比如上述就是通过获取配置中maxAttempts的值，我们可以在application.yml设置。上述其实省略掉了SpEL表达式#{....}，运行结果的话可以发现方法执行了4次..
maxAttempts: 4 我们可以使用SpEL表达式
@Retryable(value = IllegalAccessException.class, maxAttemptsExpression = "#{1+1}") public void service3_1() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException("manual exception"); } @Retryable(value = IllegalAccessException.class, maxAttemptsExpression = "#{${maxAttempts}}")//效果和上面的一样 public void service3_2() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException("manual exception"); } 接着我们下面来看看exceptionExpression, 一样也是写SpEL表达式
@Retryable(value = IllegalAccessException.class, exceptionExpression = "message.contains('test')") public void service4(String exceptionMessage) throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(exceptionMessage); } @Retryable(value = IllegalAccessException.class, exceptionExpression = "#{message.contains('test')}") public void service4_3(String exceptionMessage) throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(exceptionMessage); } 上面的表达式exceptionExpression = "message.contains('test')"的作用其实是获取到抛出来exception的message(调用了getMessage()方法)，然后判断message的内容里面是否包含了test字符串，如果包含的话就会执行重试。所以如果调用方法的时候传入的参数exceptionMessage中包含了test字符串的话就会执行重试。
但这里值得注意的是, Spring Retry 1.2.5之后exceptionExpression是可以省略掉#{...}
Since Spring Retry 1.2.5, for
exceptionExpression, templated expressions (#{...}) are deprecated in favor of simple expression strings (message.contains('this can be retried')).
使用1.2.5之后的版本运行是没有问题的
<dependency> <groupId>org.springframework.retry</groupId> <artifactId>spring-retry</artifactId> <version>1.3.0</version> </dependency> 但是如果使用1.2.5版本之前包括1.2.5版本的话，运行的时候会报错如下：
2021-01-06 09:52:45.209 INFO 23220 --- [ main] org.example.RetryService : do something... 2021-01-06T09:52:45.209178200 org.springframework.expression.spel.SpelEvaluationException: EL1001E: Type conversion problem, cannot convert from java.lang.String to java.lang.Boolean at org.springframework.expression.spel.support.StandardTypeConverter.convertValue(StandardTypeConverter.java:75) at org.springframework.expression.common.ExpressionUtils.convertTypedValue(ExpressionUtils.java:57) at org.springframework.expression.common.LiteralExpression.getValue(LiteralExpression.java:106) at org.springframework.retry.policy.ExpressionRetryPolicy.canRetry(ExpressionRetryPolicy.java:113) at org.springframework.retry.support.RetryTemplate.canRetry(RetryTemplate.java:375) at org.springframework.retry.support.RetryTemplate.doExecute(RetryTemplate.java:304) at org.springframework.retry.support.RetryTemplate.execute(RetryTemplate.java:164) at org.springframework.retry.interceptor.RetryOperationsInterceptor.invoke(RetryOperationsInterceptor.java:118) at org.springframework.retry.annotation.AnnotationAwareRetryOperationsInterceptor.invoke(AnnotationAwareRetryOperationsInterceptor.java:153) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749) at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:691) at org.example.RetryService$$EnhancerBySpringCGLIB$$d321a75e.service4(<generated>) at org.example.RetryServiceTest.testService4_2(RetryServiceTest.java:46) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:566) at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:686) at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60) at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131) at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149) at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140) at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84) at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115) at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105) at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45) at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37) at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104) at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:212) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:208) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:137) at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:71) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at java.base/java.util.ArrayList.forEach(ArrayList.java:1540) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125) at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135) at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123) at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73) at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122) at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80) at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32) at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57) at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:248) at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$5(DefaultLauncher.java:211) at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:226) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:199) at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:132) at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71) at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33) at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220) at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53) Caused by: org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Boolean] for value 'message.contains('test')'; nested exception is java.lang.IllegalArgumentException: Invalid boolean value 'message.contains('test')' at org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:47) at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:191) at org.springframework.expression.spel.support.StandardTypeConverter.convertValue(StandardTypeConverter.java:70) ... 76 more Caused by: java.lang.IllegalArgumentException: Invalid boolean value 'message.contains('test')' at org.springframework.core.convert.support.StringToBooleanConverter.convert(StringToBooleanConverter.java:63) at org.springframework.core.convert.support.StringToBooleanConverter.convert(StringToBooleanConverter.java:31) at org.springframework.core.convert.support.GenericConversionService$ConverterAdapter.convert(GenericConversionService.java:385) at org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:41) ... 78 more 还可以在表达式中执行一个方法，前提是方法的类在spring容器中注册了，@retryService其实就是获取bean name为retryService的bean，然后调用里面的checkException方法，传入的参数为#root，它其实就是抛出来的exception对象。一样的也是可以省略#{...}
@Retryable(value = IllegalAccessException.class, exceptionExpression = "#{@retryService.checkException(#root)}") public void service5(String exceptionMessage) throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(exceptionMessage); } @Retryable(value = IllegalAccessException.class, exceptionExpression = "@retryService.checkException(#root)") public void service5_1(String exceptionMessage) throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(exceptionMessage); } public boolean checkException(Exception e) { log.error("error message:{}", e.getMessage()); return true; //返回true的话表明会执行重试，如果返回false则不会执行重试 } 运行结果：
2021-01-06 13:33:52.913 INFO 23052 --- [ main] org.example.RetryService : do something... 2021-01-06T13:33:52.913404 2021-01-06 13:33:52.981 ERROR 23052 --- [ main] org.example.RetryService : error message:test message 2021-01-06 13:33:53.990 ERROR 23052 --- [ main] org.example.RetryService : error message:test message 2021-01-06 13:33:53.990 INFO 23052 --- [ main] org.example.RetryService : do something... 2021-01-06T13:33:53.990947400 2021-01-06 13:33:53.990 ERROR 23052 --- [ main] org.example.RetryService : error message:test message 2021-01-06 13:33:54.992 ERROR 23052 --- [ main] org.example.RetryService : error message:test message 2021-01-06 13:33:54.992 INFO 23052 --- [ main] org.example.RetryService : do something... 2021-01-06T13:33:54.992342900 当然还有更多表达式的用法了...
@Retryable(exceptionExpression = "#{#root instanceof T(java.lang.IllegalAccessException)}") //判断exception的类型 public void service5_2(String exceptionMessage) { log.info("do something... {}", LocalDateTime.now()); throw new NullPointerException(exceptionMessage); } @Retryable(exceptionExpression = "#root instanceof T(java.lang.IllegalAccessException)") public void service5_3(String exceptionMessage) { log.info("do something... {}", LocalDateTime.now()); throw new NullPointerException(exceptionMessage); } @Retryable(exceptionExpression = "myMessage.contains('test')") //查看自定义的MyException中的myMessage的值是否包含test字符串 public void service5_4(String exceptionMessage) throws MyException { log.info("do something... {}", LocalDateTime.now()); throw new MyException(exceptionMessage); //自定义的exception } @Retryable(exceptionExpression = "#root.myMessage.contains('test')") //和上面service5_4方法的效果一样 public void service5_5(String exceptionMessage) throws MyException { log.info("do something... {}", LocalDateTime.now()); throw new MyException(exceptionMessage); } package org.example; import lombok.Getter; import lombok.Setter; @Getter @Setter public class MyException extends Exception { private String myMessage; public MyException(String myMessage) { this.myMessage = myMessage; } } 下面再来看看另一个配置exclude
@Retryable(exclude = MyException.class) public void service6(String exceptionMessage) throws MyException { log.info("do something... {}", LocalDateTime.now()); throw new MyException(exceptionMessage); } 这个exclude属性可以帮我们排除一些我们不想重试的异常
最后我们来看看这个backoff 重试等待策略, 默认使用@Backoff注解。
我们先来看看这个@Backoff的value属性,用于设置重试间隔
@Retryable(value = IllegalAccessException.class, backoff = @Backoff(value = 2000)) public void service7() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(); } 运行结果可以看出来重试的间隔为2秒
2021-01-06 14:47:38.036 INFO 21116 --- [ main] org.example.RetryService : do something... 2021-01-06T14:47:38.036732600 2021-01-06 14:47:40.038 INFO 21116 --- [ main] org.example.RetryService : do something... 2021-01-06T14:47:40.037753600 2021-01-06 14:47:42.046 INFO 21116 --- [ main] org.example.RetryService : do something... 2021-01-06T14:47:42.046642900 java.lang.IllegalAccessException at org.example.RetryService.service7(RetryService.java:113) ... 接下来介绍@Backoff的delay属性，它与value属性不能共存，当delay不设置的时候会去读value属性设置的值，如果delay设置的话则会忽略value属性
@Retryable(value = IllegalAccessException.class, backoff = @Backoff(value = 2000,delay = 500)) public void service8() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(); } 运行结果可以看出，重试的时间间隔为500ms
2021-01-06 15:22:42.271 INFO 13512 --- [ main] org.example.RetryService : do something... 2021-01-06T15:22:42.271504800 2021-01-06 15:22:42.772 INFO 13512 --- [ main] org.example.RetryService : do something... 2021-01-06T15:22:42.772234900 2021-01-06 15:22:43.273 INFO 13512 --- [ main] org.example.RetryService : do something... 2021-01-06T15:22:43.273246700 java.lang.IllegalAccessException at org.example.RetryService.service8(RetryService.java:121) 接下来我们来看``@Backoff的multiplier`的属性, 指定延迟倍数, 默认为0。
@Retryable(value = IllegalAccessException.class,maxAttempts = 4, backoff = @Backoff(delay = 2000, multiplier = 2)) public void service9() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(); } multiplier设置为2，则表示第一次重试间隔为2s，第二次为4秒，第三次为8s
运行结果如下：
2021-01-06 15:58:07.458 INFO 23640 --- [ main] org.example.RetryService : do something... 2021-01-06T15:58:07.458245500 2021-01-06 15:58:09.478 INFO 23640 --- [ main] org.example.RetryService : do something... 2021-01-06T15:58:09.478681300 2021-01-06 15:58:13.478 INFO 23640 --- [ main] org.example.RetryService : do something... 2021-01-06T15:58:13.478921900 2021-01-06 15:58:21.489 INFO 23640 --- [ main] org.example.RetryService : do something... 2021-01-06T15:58:21.489240600 java.lang.IllegalAccessException at org.example.RetryService.service9(RetryService.java:128) ... 接下来我们来看看这个@Backoff的maxDelay属性,设置最大的重试间隔，当超过这个最大的重试间隔的时候，重试的间隔就等于maxDelay的值
@Retryable(value = IllegalAccessException.class,maxAttempts = 4, backoff = @Backoff(delay = 2000, multiplier = 2,maxDelay = 5000)) public void service10() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(); } 运行结果：
2021-01-06 16:12:37.377 INFO 5024 --- [ main] org.example.RetryService : do something... 2021-01-06T16:12:37.377616100 2021-01-06 16:12:39.381 INFO 5024 --- [ main] org.example.RetryService : do something... 2021-01-06T16:12:39.381299400 2021-01-06 16:12:43.382 INFO 5024 --- [ main] org.example.RetryService : do something... 2021-01-06T16:12:43.382169500 2021-01-06 16:12:48.396 INFO 5024 --- [ main] org.example.RetryService : do something... 2021-01-06T16:12:48.396327600 java.lang.IllegalAccessException at org.example.RetryService.service10(RetryService.java:135) 可以最后的最大重试间隔是5秒
@Recover当@Retryable方法重试失败之后，最后就会调用@Recover方法。用于@Retryable失败时的“兜底”处理方法。 @Recover的方法必须要与@Retryable注解的方法保持一致，第一入参为要重试的异常，其他参数与@Retryable保持一致，返回值也要一样，否则无法执行！
@Retryable(value = IllegalAccessException.class) public void service11() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); throw new IllegalAccessException(); } @Recover public void recover11(IllegalAccessException e) { log.info("service retry after Recover => {}", e.getMessage()); } //========================= @Retryable(value = ArithmeticException.class) public int service12() throws IllegalAccessException { log.info("do something... {}", LocalDateTime.now()); return 1 / 0; } @Recover public int recover12(ArithmeticException e) { log.info("service retry after Recover => {}", e.getMessage()); return 0; } //========================= @Retryable(value = ArithmeticException.class) public int service13(String message) throws IllegalAccessException { log.info("do something... {},{}", message, LocalDateTime.now()); return 1 / 0; } @Recover public int recover13(ArithmeticException e, String message) { log.info("{},service retry after Recover => {}", message, e.getMessage()); return 0; } @CircuitBreaker熔断模式：指在具体的重试机制下失败后打开断路器，过了一段时间，断路器进入半开状态，允许一个进入重试，若失败再次进入断路器，成功则关闭断路器，注解为
@CircuitBreaker,具体包括熔断打开时间、重置过期时间
// openTimeout时间范围内失败maxAttempts次数后，熔断打开resetTimeout时长 @CircuitBreaker(openTimeout = 1000, resetTimeout = 3000, value = NullPointerException.class) public void circuitBreaker(int num) { log.info(" 进入断路器方法num={}", num); if (num > 8) return; Integer n = null; System.err.println(1 / n); } @Recover public void recover(NullPointerException e) { log.info("service retry after Recover => {}", e.getMessage()); } 测试方法
@Test public void testCircuitBreaker() throws InterruptedException { System.err.println("尝试进入断路器方法，并触发异常..."); retryService.circuitBreaker(1); retryService.circuitBreaker(1); retryService.circuitBreaker(9); retryService.circuitBreaker(9); System.err.println("在openTimeout 1秒之内重试次数为2次，未达到触发熔断, 断路器依然闭合..."); TimeUnit.SECONDS.sleep(1); System.err.println("超过openTimeout 1秒之后, 因为未触发熔断，所以重试次数重置，可以正常访问...,继续重试3次方法..."); retryService.circuitBreaker(1); retryService.circuitBreaker(1); retryService.circuitBreaker(1); System.err.println("在openTimeout 1秒之内重试次数为3次，达到触发熔断，不会执行重试，只会执行恢复方法..."); retryService.circuitBreaker(1); TimeUnit.SECONDS.sleep(2); retryService.circuitBreaker(9); TimeUnit.SECONDS.sleep(3); System.err.println("超过resetTimeout 3秒之后，断路器重新闭合...,可以正常访问"); retryService.circuitBreaker(9); retryService.circuitBreaker(9); retryService.circuitBreaker(9); retryService.circuitBreaker(9); retryService.circuitBreaker(9); } 运行结果：
尝试进入断路器方法，并触发异常... 2021-01-07 21:44:20.842 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1 2021-01-07 21:44:20.844 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null 2021-01-07 21:44:20.845 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1 2021-01-07 21:44:20.845 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null 2021-01-07 21:44:20.845 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9 2021-01-07 21:44:20.845 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9 在openTimeout 1秒之内重试次数为2次，未达到触发熔断, 断路器依然闭合... 超过openTimeout 1秒之后, 因为未触发熔断，所以重试次数重置，可以正常访问...,继续重试3次方法... 2021-01-07 21:44:21.846 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1 2021-01-07 21:44:21.847 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null 2021-01-07 21:44:21.847 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1 2021-01-07 21:44:21.847 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null 2021-01-07 21:44:21.847 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1 2021-01-07 21:44:21.848 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null 在openTimeout 1秒之内重试次数为3次，达到触发熔断，不会执行重试，只会执行恢复方法... 2021-01-07 21:44:21.848 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null 2021-01-07 21:44:23.853 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null 超过resetTimeout 3秒之后，断路器重新闭合...,可以正常访问 2021-01-07 21:44:26.853 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9 2021-01-07 21:44:26.854 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9 2021-01-07 21:44:26.855 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9 2021-01-07 21:44:26.855 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9 2021-01-07 21:44:26.856 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9 package org.example; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.retry.backoff.FixedBackOffPolicy; import org.springframework.retry.policy.SimpleRetryPolicy; import org.springframework.retry.support.RetryTemplate; @Configuration public class AppConfig { @Bean public RetryTemplate retryTemplate() { RetryTemplate retryTemplate = new RetryTemplate(); SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy(); //设置重试策略 retryPolicy.setMaxAttempts(2); retryTemplate.setRetryPolicy(retryPolicy); FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy(); //设置退避策略 fixedBackOffPolicy.setBackOffPeriod(2000L); retryTemplate.setBackOffPolicy(fixedBackOffPolicy); return retryTemplate; } } 可以看到这些配置跟我们直接写注解的方式是差不多的，这里就不过多的介绍了。。
package org.example; import org.junit.jupiter.api.Test; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.boot.test.context.SpringBootTest; import org.springframework.retry.RetryCallback; import org.springframework.retry.RetryContext; import org.springframework.retry.support.RetryTemplate; @SpringBootTest public class RetryTemplateTest { @Autowired private RetryTemplate retryTemplate; @Autowired private RetryTemplateService retryTemplateService; @Test void test1() throws IllegalAccessException { retryTemplate.execute(new RetryCallback<Object, IllegalAccessException>() { @Override public Object doWithRetry(RetryContext context) throws IllegalAccessException { retryTemplateService.service1(); return null; } }); } @Test void test2() throws IllegalAccessException { retryTemplate.execute(new RetryCallback<Object, IllegalAccessException>() { @Override public Object doWithRetry(RetryContext context) throws IllegalAccessException { retryTemplateService.service1(); return null; } }, new RecoveryCallback<Object>() { @Override public Object recover(RetryContext context) throws Exception { log.info("RecoveryCallback...."); return null; } }); } } RetryOperations定义重试的API，RetryTemplate是API的模板模式实现，实现了重试和熔断。提供的API如下:
package org.springframework.retry; import org.springframework.retry.support.DefaultRetryState; /** * Defines the basic set of operations implemented by {@link RetryOperations} to execute * operations with configurable retry behaviour. * * @author Rob Harrop * @author Dave Syer */ public interface RetryOperations { /** * Execute the supplied {@link RetryCallback} with the configured retry semantics. See * implementations for configuration details. * @param <T> the return value * @param retryCallback the {@link RetryCallback} * @param <E> the exception to throw * @return the value returned by the {@link RetryCallback} upon successful invocation. * @throws E any {@link Exception} raised by the {@link RetryCallback} upon * unsuccessful retry. * @throws E the exception thrown */ <T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback) throws E; /** * Execute the supplied {@link RetryCallback} with a fallback on exhausted retry to * the {@link RecoveryCallback}. See implementations for configuration details. * @param recoveryCallback the {@link RecoveryCallback} * @param retryCallback the {@link RetryCallback} {@link RecoveryCallback} upon * @param <T> the type to return * @param <E> the type of the exception * @return the value returned by the {@link RetryCallback} upon successful invocation, * and that returned by the {@link RecoveryCallback} otherwise. * @throws E any {@link Exception} raised by the unsuccessful retry. */ <T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback, RecoveryCallback<T> recoveryCallback) throws E; /** * A simple stateful retry. Execute the supplied {@link RetryCallback} with a target * object for the attempt identified by the {@link DefaultRetryState}. Exceptions * thrown by the callback are always propagated immediately so the state is required * to be able to identify the previous attempt, if there is one - hence the state is * required. Normal patterns would see this method being used inside a transaction, * where the callback might invalidate the transaction if it fails. * * See implementations for configuration details. * @param retryCallback the {@link RetryCallback} * @param retryState the {@link RetryState} * @param <T> the type of the return value * @param <E> the type of the exception to return * @return the value returned by the {@link RetryCallback} upon successful invocation, * and that returned by the {@link RecoveryCallback} otherwise. * @throws E any {@link Exception} raised by the {@link RecoveryCallback}. * @throws ExhaustedRetryException if the last attempt for this state has already been * reached */ <T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback, RetryState retryState) throws E, ExhaustedRetryException; /** * A stateful retry with a recovery path. Execute the supplied {@link RetryCallback} * with a fallback on exhausted retry to the {@link RecoveryCallback} and a target * object for the retry attempt identified by the {@link DefaultRetryState}. * @param recoveryCallback the {@link RecoveryCallback} * @param retryState the {@link RetryState} * @param retryCallback the {@link RetryCallback} * @param <T> the return value type * @param <E> the exception type * @see #execute(RetryCallback, RetryState) * @return the value returned by the {@link RetryCallback} upon successful invocation, * and that returned by the {@link RecoveryCallback} otherwise. * @throws E any {@link Exception} raised by the {@link RecoveryCallback} upon * unsuccessful retry. */ <T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback, RecoveryCallback<T> recoveryCallback, RetryState retryState) throws E; } 下面主要介绍一下RetryTemplate配置的时候，需要设置的重试策略和退避策略
RetryPolicy是一个接口, 然后有很多具体的实现，我们先来看看它的接口中定义了什么方法
package org.springframework.retry; import java.io.Serializable; /** * A {@link RetryPolicy} is responsible for allocating and managing resources needed by * {@link RetryOperations}. The {@link RetryPolicy} allows retry operations to be aware of * their context. Context can be internal to the retry framework, e.g. to support nested * retries. Context can also be external, and the {@link RetryPolicy} provides a uniform * API for a range of different platforms for the external context. * * @author Dave Syer * */ public interface RetryPolicy extends Serializable { /** * @param context the current retry status * @return true if the operation can proceed */ boolean canRetry(RetryContext context); /** * Acquire resources needed for the retry operation. The callback is passed in so that * marker interfaces can be used and a manager can collaborate with the callback to * set up some state in the status token. * @param parent the parent context if we are in a nested retry. * @return a {@link RetryContext} object specific to this policy. * */ RetryContext open(RetryContext parent); /** * @param context a retry status created by the {@link #open(RetryContext)} method of * this policy. */ void close(RetryContext context); /** * Called once per retry attempt, after the callback fails. * @param context the current status object. * @param throwable the exception to throw */ void registerThrowable(RetryContext context, Throwable throwable); } 我们来看看他有什么具体的实现类
看一下退避策略，退避是指怎么去做下一次的重试，在这里其实就是等待多长时间。
listener可以监听重试，并执行对应的回调方法
package org.springframework.retry; /** * Interface for listener that can be used to add behaviour to a retry. Implementations of * {@link RetryOperations} can chose to issue callbacks to an interceptor during the retry * lifecycle. * * @author Dave Syer * */ public interface RetryListener { /** * Called before the first attempt in a retry. For instance, implementers can set up * state that is needed by the policies in the {@link RetryOperations}. The whole * retry can be vetoed by returning false from this method, in which case a * {@link TerminatedRetryException} will be thrown. * @param <T> the type of object returned by the callback * @param <E> the type of exception it declares may be thrown * @param context the current {@link RetryContext}. * @param callback the current {@link RetryCallback}. * @return true if the retry should proceed. */ <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback); /** * Called after the final attempt (successful or not). Allow the interceptor to clean * up any resource it is holding before control returns to the retry caller. * @param context the current {@link RetryContext}. * @param callback the current {@link RetryCallback}. * @param throwable the last exception that was thrown by the callback. * @param <E> the exception type * @param <T> the return value */ <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable); /** * Called after every unsuccessful attempt at a retry. * @param context the current {@link RetryContext}. * @param callback the current {@link RetryCallback}. * @param throwable the last exception that was thrown by the callback. * @param <T> the return value * @param <E> the exception to throw */ <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable); } 使用如下：
自定义一个Listener
package org.example; import lombok.extern.slf4j.Slf4j; import org.springframework.retry.RetryCallback; import org.springframework.retry.RetryContext; import org.springframework.retry.listener.RetryListenerSupport; @Slf4j public class DefaultListenerSupport extends RetryListenerSupport { @Override public <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) { log.info("onClose"); super.close(context, callback, throwable); } @Override public <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) { log.info("onError"); super.onError(context, callback, throwable); } @Override public <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) { log.info("onOpen"); return super.open(context, callback); } } 把listener设置到retryTemplate中
package org.example; import lombok.extern.slf4j.Slf4j; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.retry.backoff.FixedBackOffPolicy; import org.springframework.retry.policy.SimpleRetryPolicy; import org.springframework.retry.support.RetryTemplate; @Configuration @Slf4j public class AppConfig { @Bean public RetryTemplate retryTemplate() { RetryTemplate retryTemplate = new RetryTemplate(); SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy(); //设置重试策略 retryPolicy.setMaxAttempts(2); retryTemplate.setRetryPolicy(retryPolicy); FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy(); //设置退避策略 fixedBackOffPolicy.setBackOffPeriod(2000L); retryTemplate.setBackOffPolicy(fixedBackOffPolicy); retryTemplate.registerListener(new DefaultListenerSupport()); //设置retryListener return retryTemplate; } } 测试结果：
2021-01-08 10:48:05.663 INFO 20956 --- [ main] org.example.DefaultListenerSupport : onOpen 2021-01-08 10:48:05.663 INFO 20956 --- [ main] org.example.RetryTemplateService : do something... 2021-01-08 10:48:05.663 INFO 20956 --- [ main] org.example.DefaultListenerSupport : onError 2021-01-08 10:48:07.664 INFO 20956 --- [ main] org.example.RetryTemplateService : do something... 2021-01-08 10:48:07.664 INFO 20956 --- [ main] org.example.DefaultListenerSupport : onError 2021-01-08 10:48:07.664 INFO 20956 --- [ main] org.example.RetryTemplateTest : RecoveryCallback.... 2021-01-08 10:48:07.664 INFO 20956 --- [ main] org.example.DefaultListenerSupport : onClose usage-of-exceptionexpression-in-spring-retry
