目录一、环境搭建二、RetryTemplate2.1 RetryTemplate2.2 RetryListener2.3 回退策略2.3.1 FixedBackOffPolicy2.3.2 ExponentialBackOffPolicy2.4 重试策略2.5 RetryCallback2.6 核心使用三、EnableRetry四、Retryable
spring retry主要实现了重试和熔断。
不适合重试的场景：
参数校验不合法、写操作等（要考虑写是否幂等）都不适合重试。
适合重试的场景：
远程调用超时、网络突然中断等可以重试。
在spring retry中可以指定需要重试的异常类型，并设置每次重试的间隔以及如果重试失败是继续重试还是熔断（停止重试）。
一、环境搭建
加入SpringRetry依赖，SpringRetry使用AOP实现，所以也需要加入AOP包
<!-- SpringRetry --><dependency> <groupId>org.springframework.retry</groupId> <artifactId>spring-retry</artifactId></dependency><dependency> <groupId>org.springframework</groupId> <artifactId>spring-aspects</artifactId></dependency>
官方文档
二、RetryTemplate
2.1 RetryTemplate RetryTemplate封装了Retry基本操作 org.springframework.retry.support.RetryTemplate RetryTemplate中可以指定监听、回退策略、重试策略等 只需要正常new RetryTemplate()即可使用
2.2 RetryListener
RetryListener指定了当执行过程中出现错误时的回调
org.springframework.retry.RetryListener
package org.springframework.retry;public interface RetryListener { /** * 任务开始执行时调用，只调用一次 */ <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback); /** * 任务执行结束时(包含重试)调用，只调用一次 */ <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable); /** * 出现错误时回调 */ <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable);}
配置之后在RetryTemplate中指定
2.3 回退策略
2.3.1 FixedBackOffPolicy
当出现错误时延迟多少时间继续调用
FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy();fixedBackOffPolicy.setBackOffPeriod(1000L);retryTemplate.setBackOffPolicy(fixedBackOffPolicy);
配置之后在RetryTemplate中指定
2.3.2 ExponentialBackOffPolicy
当出现错误时第一次按照指定延迟时间延迟后按照指数进行延迟
// 指数回退(秒)，第一次回退1s，第二次回退2s，第三次4秒，第四次8秒ExponentialBackOffPolicy exponentialBackOffPolicy = new ExponentialBackOffPolicy();exponentialBackOffPolicy.setInitialInterval(1000L);exponentialBackOffPolicy.setMultiplier(2);retryTemplate.setBackOffPolicy(exponentialBackOffPolicy);
配置之后在RetryTemplate中指定
2.4 重试策略
重试策略主要指定出现错误时重试次数
// 重试策略SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy();retryPolicy.setMaxAttempts(5);retryTemplate.setRetryPolicy(retryPolicy);
配置之后在RetryTemplate中指定
2.5 RetryCallback
RetryCallback为retryTemplate.execute时执行的回调
public final <T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback) throws E
2.6 核心使用
可以使用RetryTemplate完成简单使用配置retryTemplate
指定回退策略为ExponentialBackOffPolicy 指定重试策略为SimpleRetryPolicy 指定监听器RetryListener
import com.codecoord.util.PrintUtil;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;import org.springframework.retry.RetryCallback;import org.springframework.retry.RetryContext;import org.springframework.retry.RetryListener;import org.springframework.retry.backoff.ExponentialBackOffPolicy;import org.springframework.retry.policy.SimpleRetryPolicy;import org.springframework.retry.support.RetryTemplate;@Configurationpublic class RetryTemplateConfig { /** * 注入retryTemplate */ @Bean public RetryTemplate retryTemplate() { RetryTemplate retryTemplate = new RetryTemplate(); /// 回退固定时间(秒) /* FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy(); fixedBackOffPolicy.setBackOffPeriod(1000L); retryTemplate.setBackOffPolicy(fixedBackOffPolicy);*/ // 指数回退(秒)，第一次回退1s，第二次回退2s ExponentialBackOffPolicy exponentialBackOffPolicy = new ExponentialBackOffPolicy(); exponentialBackOffPolicy.setInitialInterval(1000L); exponentialBackOffPolicy.setMultiplier(2); retryTemplate.setBackOffPolicy(exponentialBackOffPolicy); // 重试策略 SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy(); retryPolicy.setMaxAttempts(5); retryTemplate.setRetryPolicy(retryPolicy); // 设置监听器，open和close分别在启动和结束时执行一次 RetryListener[] listeners = { new RetryListener() { @Override public <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) { PrintUtil.print("open"); return true; } @Override public <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) { PrintUtil.print("close"); } @Override public <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) { PrintUtil.print("onError"); } } }; retryTemplate.setListeners(listeners); return retryTemplate; }}
在controller中注入RetryTemplate使用，也可以是在service中
@RestControllerpublic class SpringRetryController { @Resource private RetryTemplate retryTemplate; private static int count = 0; @RequestMapping("/retry") public Object retry() { try { count = 0; retryTemplate.execute((RetryCallback<Void, RuntimeException>) context -> { // 业务代码 // .... // 模拟抛出异常 ++count; throw new RuntimeException("抛出异常"); }); } catch (RuntimeException e) { System.out.println("Exception"); } return "retry = " + count; }}
访问retry接口，然后观察日志输出
18:27:20.648 – http-nio-8888-exec-1 – open18:27:20.649 – http-nio-8888-exec-1 – retryTemplate.execute执行18:27:20.649 – http-nio-8888-exec-1 – onError18:27:21.658 – http-nio-8888-exec-1 – retryTemplate.execute执行18:27:21.658 – http-nio-8888-exec-1 – onError18:27:23.670 – http-nio-8888-exec-1 – retryTemplate.execute执行18:27:23.670 – http-nio-8888-exec-1 – onError18:27:27.679 – http-nio-8888-exec-1 – retryTemplate.execute执行18:27:27.679 – http-nio-8888-exec-1 – onError18:27:35.681 – http-nio-8888-exec-1 – retryTemplate.execute执行18:27:35.681 – http-nio-8888-exec-1 – onError18:27:35.681 – http-nio-8888-exec-1 – close
三、EnableRetry
@EnableRetry开启重试，在类上指定的时候方法将默认执行，重试三次定义service，开启@EnableRetry注解和指定@Retryable，重试可以参考后面一节
import org.springframework.retry.annotation.Retryable;public interface RetryService { /** * 重试方法调用 */ @Retryable void retryServiceCall();}
import org.springframework.retry.annotation.EnableRetry;import org.springframework.stereotype.Service;@EnableRetry@Servicepublic class RetryServiceImpl implements RetryService { @Override public void retryServiceCall() { PrintUtil.print("方法调用.."); throw new RuntimeException("手工异常"); }}
controller中注入service
@RequestMapping("/retryAnnotation")public Object retryAnnotation() { retryService.retryServiceCall(); return "retryAnnotation";}
将会默认重试
18:46:48.721 – http-nio-8888-exec-1 – 方法调用..18:46:49.724 – http-nio-8888-exec-1 – 方法调用..18:46:50.730 – http-nio-8888-exec-1 – 方法调用..java.lang.RuntimeException: 手工异常
四、Retryable
用于需要重试的方法上的注解有以下几个属性
Retryable注解参数
value：指定发生的异常进行重试 include：和value一样，默认空，当exclude也为空时，所有异常都重试 exclude：指定异常不重试，默认空，当include也为空时，所有异常都重试 maxAttemps：重试次数，默认3 backoff：重试补偿机制，默认没有
@Backoff 注解 重试补偿策略
不设置参数时，默认使用FixedBackOffPolicy（指定等待时间），重试等待1000ms 设置delay，使用FixedBackOffPolicy（指定等待设置delay和maxDealy时，重试等待在这两个值之间均态分布） 设置delay、maxDealy、multiplier，使用 ExponentialBackOffPolicy（指数级重试间隔的实现），multiplier即指定延迟倍数，比如delay=5000L，multiplier=2,则第一次重试为5秒，第二次为10秒，第三次为20秒
@Target({ ElementType.METHOD, ElementType.TYPE })@Retention(RetentionPolicy.RUNTIME)@Documentedpublic @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; /** * @return an expression evaluated to the maximum number of attempts (including the first failure), defaults to 3 * Overrides {@link #maxAttempts()}. * @date 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(); /** * 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. * @date 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)@Documentedpublic @interface Backoff { /** * Synonym for {@link #delay()}. * * @return the delay in milliseconds (default 1000) */ long value() default 1000; /** * 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. * @date 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) * @date 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) * @date 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;}
在需要重试的方法上配置对应的重试次数、重试异常的异常类型、设置回退延迟时间、重试策略、方法监听名称
@Componentpublic class PlatformClassService { @Retryable( // 重试异常的异常类型 value = {Exception.class}, // 最大重试次数 maxAttempts = 5, // 设置回退延迟时间 backoff = @Backoff(delay = 500), // 配置回调方法名称 listeners = "retryListener" ) public void call() { System.out.println("call..."); throw new RuntimeException("手工异常"); }}
// 初始延迟2秒，然后之后验收1.5倍延迟重试，总重试次数4@Retryable(value = {Exception.class}, maxAttempts = 4, backoff = @Backoff(delay = 2000L, multiplier = 1.5))
监听方法，在配置类中进行配置
/** * 注解调用 */@Beanpublic RetryListener retryListener() { return new RetryListener() { @Override public <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) { System.out.println("open context = " + context + ", callback = " + callback); // 返回true继续执行后续调用 return true; } @Override public <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) { System.out.println("close context = " + context + ", callback = " + callback); } @Override public <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) { System.out.println("onError context = " + context + ", callback = " + callback); } };}
调用服务
@RestControllerpublic class SpringRetryController { @Resource private PlatformClassService platformClassService; @RequestMapping("/retryPlatformCall") public Object retryPlatformCall() { try { platformClassService.call(); } catch (Exception e) { return "尝试调用失败"; } return "retryPlatformCall"; }}
调用结果
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