目錄一、環境搭建二、RetryTemplate2.1 RetryTemplate2.2 RetryListener2.3 回退策略2.3.1 FixedBackOffPolicy2.3.2 ExponentialBackOffPolicy2.4 重試策略2.5 RetryCallback2.6 核心使用三、EnableRetry四、Retryable

spring retry主要實現了重試和熔斷。

不適合重試的場景：

參數校驗不合法、寫操作等（要考慮寫是否冪等）都不適合重試。

適合重試的場景：

遠程調用超時、網絡突然中斷等可以重試。

在spring retry中可以指定需要重試的異常類型，并設置每次重試的間隔以及如果重試失敗是繼續重試還是熔斷（停止重試）。

一、環境搭建

加入SpringRetry依賴，SpringRetry使用AOP實現，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>

官方文檔

二、RetryTemplate2.1 RetryTemplate RetryTemplate封裝了Retry基本操作 org.springframework.retry.support.RetryTemplate RetryTemplate中可以指定監聽、回退策略、重試策略等 只需要正常new RetryTemplate()即可使用2.2 RetryListener

RetryListener指定了當執行過程中出現錯誤時的回調

org.springframework.retry.RetryListener

package org.springframework.retry;public interface RetryListener { /** * 任務開始執行時調用，只調用一次 */ <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback); /** * 任務執行結束時(包含重試)調用，只調用一次 */ <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable); /** * 出現錯誤時回調 */ <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

當出現錯誤時延遲多少時間繼續調用

FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy();fixedBackOffPolicy.setBackOffPeriod(1000L);retryTemplate.setBackOffPolicy(fixedBackOffPolicy);

配置之后在RetryTemplate中指定

2.3.2 ExponentialBackOffPolicy

當出現錯誤時第一次按照指定延遲時間延遲后按照指數進行延遲

// 指數回退(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 重試策略

重試策略主要指定出現錯誤時重試次數

// 重試策略SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy();retryPolicy.setMaxAttempts(5);retryTemplate.setRetryPolicy(retryPolicy);

配置之后在RetryTemplate中指定

2.5 RetryCallback

RetryCallback為retryTemplate.execute時執行的回調

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完成簡單使用配置retryTemplate

指定回退策略為ExponentialBackOffPolicy 指定重試策略為SimpleRetryPolicy 指定監聽器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();/// 回退固定時間(秒) /* FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy();fixedBackOffPolicy.setBackOffPeriod(1000L);retryTemplate.setBackOffPolicy(fixedBackOffPolicy);*/// 指數回退(秒)，第一次回退1s，第二次回退2sExponentialBackOffPolicy exponentialBackOffPolicy = new ExponentialBackOffPolicy();exponentialBackOffPolicy.setInitialInterval(1000L);exponentialBackOffPolicy.setMultiplier(2);retryTemplate.setBackOffPolicy(exponentialBackOffPolicy);// 重試策略SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy();retryPolicy.setMaxAttempts(5);retryTemplate.setRetryPolicy(retryPolicy);// 設置監聽器，open和close分別在啟動和結束時執行一次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 -> {// 業務代碼// ....// 模擬拋出異常++count;throw new RuntimeException('拋出異常'); });} catch (RuntimeException e) { System.out.println('Exception');}return 'retry = ' + count; }}

訪問retry接口，然后觀察日志輸出

18:27:20.648 - http-nio-8888-exec-1 - open18:27:20.649 - http-nio-8888-exec-1 - retryTemplate.execute執行18:27:20.649 - http-nio-8888-exec-1 - onError18:27:21.658 - http-nio-8888-exec-1 - retryTemplate.execute執行18:27:21.658 - http-nio-8888-exec-1 - onError18:27:23.670 - http-nio-8888-exec-1 - retryTemplate.execute執行18:27:23.670 - http-nio-8888-exec-1 - onError18:27:27.679 - http-nio-8888-exec-1 - retryTemplate.execute執行18:27:27.679 - http-nio-8888-exec-1 - onError18:27:35.681 - http-nio-8888-exec-1 - retryTemplate.execute執行18:27:35.681 - http-nio-8888-exec-1 - onError18:27:35.681 - http-nio-8888-exec-1 - close

三、EnableRetry

@EnableRetry開啟重試，在類上指定的時候方法將默認執行，重試三次定義service，開啟@EnableRetry注解和指定@Retryable，重試可以參考后面一節

import org.springframework.retry.annotation.Retryable;public interface RetryService { /** * 重試方法調用 */ @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('方法調用..');throw new RuntimeException('手工異常'); }}

controller中注入service

@RequestMapping('/retryAnnotation')public Object retryAnnotation() { retryService.retryServiceCall(); return 'retryAnnotation';}

將會默認重試

18:46:48.721 - http-nio-8888-exec-1 - 方法調用..18:46:49.724 - http-nio-8888-exec-1 - 方法調用..18:46:50.730 - http-nio-8888-exec-1 - 方法調用..java.lang.RuntimeException: 手工異常

四、Retryable

用于需要重試的方法上的注解有以下幾個屬性

Retryable注解參數

value：指定發生的異常進行重試 include：和value一樣，默認空，當exclude也為空時，所有異常都重試 exclude：指定異常不重試，默認空，當include也為空時，所有異常都重試 maxAttemps：重試次數，默認3 backoff：重試補償機制，默認沒有

@Backoff 注解 重試補償策略

不設置參數時，默認使用FixedBackOffPolicy（指定等待時間），重試等待1000ms 設置delay，使用FixedBackOffPolicy（指定等待設置delay和maxDealy時，重試等待在這兩個值之間均態分布） 設置delay、maxDealy、multiplier，使用 ExponentialBackOffPolicy（指數級重試間隔的實現），multiplier即指定延遲倍數，比如delay=5000L，multiplier=2,則第一次重試為5秒，第二次為10秒，第三次為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()} &gt; 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;}

在需要重試的方法上配置對應的重試次數、重試異常的異常類型、設置回退延遲時間、重試策略、方法監聽名稱

@Componentpublic class PlatformClassService { @Retryable(// 重試異常的異常類型value = {Exception.class},// 最大重試次數maxAttempts = 5,// 設置回退延遲時間backoff = @Backoff(delay = 500),// 配置回調方法名稱listeners = 'retryListener' ) public void call() {System.out.println('call...');throw new RuntimeException('手工異常'); }}

// 初始延遲2秒，然后之后驗收1.5倍延遲重試，總重試次數4@Retryable(value = {Exception.class}, maxAttempts = 4, backoff = @Backoff(delay = 2000L, multiplier = 1.5))

監聽方法，在配置類中進行配置

/** * 注解調用 */@Beanpublic RetryListener retryListener() { return new RetryListener() {@Overridepublic <T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback) { System.out.println('open context = ' + context + ', callback = ' + callback); // 返回true繼續執行后續調用 return true;}@Overridepublic <T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) { System.out.println('close context = ' + context + ', callback = ' + callback);}@Overridepublic <T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable) { System.out.println('onError context = ' + context + ', callback = ' + callback);} };}

調用服務

@RestControllerpublic class SpringRetryController { @Resource private PlatformClassService platformClassService;@RequestMapping('/retryPlatformCall') public Object retryPlatformCall() {try { platformClassService.call();} catch (Exception e) { return '嘗試調用失敗';}return 'retryPlatformCall'; }}

調用結果

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