SpringRetry重试框架的具体使用

• 二、retrytemplate
  
• 2.1 retrytemplate
• 2.2 retrylistener
• 2.5 retrycallback
• 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>

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;

@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

@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

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

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
@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

@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)
@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 {};

}

@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()} > 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

@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");
    }
}

// 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
  */
@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

@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

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