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

xml复制代码<!-- 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
- www.baeldung.com/spring-retr…

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

java复制代码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

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java复制代码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

java复制代码// 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

java复制代码// 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

java复制代码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;

@Configuration
public 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

java复制代码@RestController
public 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

java复制代码18:27:20.648 - http-nio-8888-exec-1 - open
18:27:20.649 - http-nio-8888-exec-1 - retryTemplate.execute执行
18:27:20.649 - http-nio-8888-exec-1 - onError
18:27:21.658 - http-nio-8888-exec-1 - retryTemplate.execute执行
18:27:21.658 - http-nio-8888-exec-1 - onError
18:27:23.670 - http-nio-8888-exec-1 - retryTemplate.execute执行
18:27:23.670 - http-nio-8888-exec-1 - onError
18:27:27.679 - http-nio-8888-exec-1 - retryTemplate.execute执行
18:27:27.679 - http-nio-8888-exec-1 - onError
18:27:35.681 - http-nio-8888-exec-1 - retryTemplate.execute执行
18:27:35.681 - http-nio-8888-exec-1 - onError
18:27:35.681 - 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

java复制代码import org.springframework.retry.annotation.Retryable;

public interface RetryService {

    /**
     * 重试方法调用
     */
    @Retryable
    void retryServiceCall();
}

java复制代码import org.springframework.retry.annotation.EnableRetry;
import org.springframework.stereotype.Service;

@EnableRetry
@Service
public 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

java复制代码@RequestMapping("/retryAnnotation")
public Object retryAnnotation() {
    retryService.retryServiceCall();
    return "retryAnnotation";
}

将会默认重试

java复制代码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

java复制代码@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;

	/**
	 * @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 {};

}

java复制代码@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;

	/**
	 * 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

java复制代码@Component
public 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");
    }
}

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java复制代码// 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

java复制代码/**
  * 注解调用
  */
@Bean
public 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

java复制代码@RestController
public 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

本文转载自: 掘金

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