关于Spring-Retry的使用

1 Spring-Retry的使用

1 Spring-Retry的简介

在日常的一些场景中, 很多需要进行重试的操作.而spring-retry是spring提供的一个基于spring的重试框架，非常简单好用.

2 Spring中的应用

1 导入maven坐标

 <dependency>
    <groupId>org.springframework.retry</groupId>
    <artifactId>spring-retry</artifactId>
    <version>1.2.2.RELEASE</version>
 </dependency>

2 添加被调用类

@Slf4j
public class RetryDemo {

    public static boolean retryMethod(Integer param) {
        int i = new Random().nextInt(param);
        log.info("随机生成的数:{}", i);

        if (1 == i) {
            log.info("为1,返回true.");
            return true;
        } else if (i < 1) {
            log.info("小于1,抛出参数异常.");
            throw new IllegalArgumentException("参数异常");
        } else if (i > 1 && i < 10) {
            log.info("大于1,小于10,抛出参数异常.");
            return false;
        } else {
            //为其他
            log.info("大于10,抛出自定义异常.");
            throw new RemoteAccessException("大于10,抛出自定义异常");
        }
    }

}

3 添加测试类

@Slf4j
public class SpringRetryTest {

    /**
     * 重试间隔时间ms,默认1000ms
     */
    private long fixedPeriodTime = 1000L;
    /**
     * 最大重试次数,默认为3
     */
    private int maxRetryTimes = 3;
    /**
     * 表示哪些异常需要重试
     * key一定要为Throwable异常的子类    Class<? extends Throwable>
     * value为true表示需要重试
     */
    private Map<Class<? extends Throwable>, Boolean> exceptionMap = new HashMap<>();


    @Test
    public void test() {

        // 1 添加异常的处理结果 true为需要重试 false为不需要重试
        exceptionMap.put(RemoteAccessException.class, true);

        // 2 构建重试模板实例
        RetryTemplate retryTemplate = new RetryTemplate();

        // 3 设置重试回退操作策略  设置重试间隔时间
        FixedBackOffPolicy backOffPolicy = new FixedBackOffPolicy();
        backOffPolicy.setBackOffPeriod(fixedPeriodTime);

        // 4 设置重试策略  设置重试次数 设置异常处理结果
        SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy(maxRetryTimes, exceptionMap);

        //5 重试模板添加重试策略 添加回退操作策略
        retryTemplate.setRetryPolicy(retryPolicy);
        retryTemplate.setBackOffPolicy(backOffPolicy);
    
        // 6 调用方法
        Boolean resp = retryTemplate.execute(
                // RetryCallback 重试回调方法
                retryContext -> {
                    boolean result = RetryDemo.retryMethod(110);
                    log.info("方法返回结果= {}", result);
                    return result;
                },
                // RecoveryCallback 异常回调方法
                retryContext -> {
                    //
                    log.info("超过最大重试次数或者抛出了未定义的异常!!!");
                    return false;
                }
        );

        log.info("接口返回结果 = {}",resp);

    }

}
/*
	// 查看结果
	[main] INFO com.cf.demo.SpringRetry.SpringRetryTest - 超过最大重试次数或者抛出了未定义的异常!!!
	[main] INFO com.cf.demo.SpringRetry.SpringRetryTest - 接口返回结果 = false
*/

从代码的书写注解可以看到,RetryTemplate对象是Spring-Retry框架的重试执行者, 由它添加重试策略,回退操作策略等(注释第五步).RetryTemplate执行重试方法(注释第六步),通过execute方法, 传入的参数是重试回调逻辑对象RetryCallback 和执行操作结束的恢复对象RecoveryCallback. 且可以切换添加的异常种类, 得知,只有添加过相应的异常,才会触发重试操作,否则直接调用RecoveryCallback对象方法.

RetryTemplate的部分源码:

	/**
	 * Keep executing the callback until it either succeeds or the policy dictates that we
	 * stop, in which case the recovery callback will be executed.
	 *
	 * @see RetryOperations#execute(RetryCallback, RecoveryCallback)
	 * @param retryCallback the {@link RetryCallback}
	 * @param recoveryCallback the {@link RecoveryCallback}
	 * @throws TerminatedRetryException if the retry has been manually terminated by a
	 * listener.
	 */
	@Override
	public final <T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback,
			RecoveryCallback<T> recoveryCallback) throws E {
		return doExecute(retryCallback, recoveryCallback, null);
	}

RetryTemplate添加重试策略源码:

	/**
	 * Setter for {@link RetryPolicy}.
	 *
	 * @param retryPolicy the {@link RetryPolicy}
	 */
	public void setRetryPolicy(RetryPolicy retryPolicy) {
		this.retryPolicy = retryPolicy;
	}

RetryPolicy接口的实现类:

AlwaysRetryPolicy：允许无限重试，直到成功，可能会导致死循环

CircuitBreakerRetryPolicy：有熔断功能的重试策略，需设置3个参数openTimeout、resetTimeout和delegate

CompositeRetryPolicy：组合重试策略，有两种组合方式，乐观组合重试策略是指只要有一个策略允许即可以重试，
悲观组合重试策略是指只要有一个策略不允许即可以重试，但不管哪种组合方式，组合中的每一个策略都会执行
    
ExceptionClassifierRetryPolicy：设置不同异常的重试策略，类似组合重试策略，区别在于这里只区分不同异常的重试
    
NeverRetryPolicy：只允许调用RetryCallback一次，不允许重试
    
SimpleRetryPolicy：固定次数重试策略，默认重试最大次数为3次，RetryTemplate默认使用的策略

TimeoutRetryPolicy：超时时间重试策略，默认超时时间为1秒，在指定的超时时间内允许重试

RetryTemplate添加回退策略源码:

	/**
	 * Setter for {@link BackOffPolicy}.
	 *
	 * @param backOffPolicy the {@link BackOffPolicy}
	 */
	public void setBackOffPolicy(BackOffPolicy backOffPolicy) {
		this.backOffPolicy = backOffPolicy;
	}

BackOffPolicy的实现类:

ExponentialBackOffPolicy：指数退避策略，需设置参数sleeper、initialInterval、maxInterval和multiplier，initialInterval指定初始休眠时间，默认100毫秒，maxInterval指定最大休眠时间，默认30秒，multiplier指定乘数，即下一次休眠时间为当前休眠时间*multiplier

ExponentialRandomBackOffPolicy：随机指数退避策略，引入随机乘数可以实现随机乘数回退

FixedBackOffPolicy：固定时间的退避策略，需设置参数sleeper和backOffPeriod，sleeper指定等待策略，默认是Thread.sleep，即线程休眠，backOffPeriod指定休眠时间，默认1秒
    
NoBackOffPolicy：无退避算法策略，每次重试时立即重试

UniformRandomBackOffPolicy：随机时间退避策略，需设置sleeper、minBackOffPeriod和maxBackOffPeriod，该策略在[minBackOffPeriod,maxBackOffPeriod之间取一个随机休眠时间，minBackOffPeriod默认500毫秒，maxBackOffPeriod默认1500毫秒

3 SpringBoot中的应用

1 导入maven坐标

 <dependency>
    <groupId>org.springframework.retry</groupId>
    <artifactId>spring-retry</artifactId>
    <version>1.2.2.RELEASE</version>
 </dependency>

 <dependency>
    <groupId>org.aspectj</groupId>
    <artifactId>aspectjweaver</artifactId>
    <version>1.9.1</version>
 </dependency>

2 添加一个管理类

@Service
@Slf4j
public class SpringRetryDemo {


    /**
     * 重试所调用方法
     * @return
     */
    // delay=2000L表示延迟2秒 multiplier=2表示两倍 即第一次重试2秒后,第二次重试4秒后,第三次重试8秒后
    @Retryable(value = {RemoteAccessException.class}, maxAttempts = 3, backoff = @Backoff(delay = 2000L, multiplier = 2))
    public boolean call(Integer param) {
        return RetryDemo.retryMethod(param);
    }

    /**
     * 超过最大重试次数或抛出没有指定重试的异常
     * @param e
     * @param param
     * @return
     */
    @Recover
    public boolean recover(Exception e, Integer param) {
        log.info("请求参数为: ", param);
        log.info("超过最大重试次数或抛出没有指定重试的异常, e = {} ", e.getMessage());
        return false;
    }

}

3 启动类上添加注解@EnableRetry

@SpringBootApplication
@EnableRetry
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}    

4 添加测试类

@RunWith(SpringRunner.class)
@SpringBootTest(classes = DemoApplication.class)
@Slf4j
public class DemoApplicationTests {

    @Autowired
    private SpringRetryDemo springRetryDemo;

    @Test
    public void testRetry() {
        boolean result = springRetryDemo.call(110);
        log.info("方法返回结果为: {}", result);
    }
}
/*	运行结果:

    随机生成的数:77
    大于10,抛出自定义异常.
    随机生成的数:23
    大于10,抛出自定义异常.
    随机生成的数:82
    大于10,抛出自定义异常.
    请求参数为: 
    超过最大重试次数或抛出没有指定重试的异常, e = 大于10,抛出自定义异常 
    方法返回结果为: false
*/

注解说明:

@Enableretry注解，启用重试功能(默认是否基于子类代理,默认是否, 即是基于Java接口代理)

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@EnableAspectJAutoProxy(proxyTargetClass = false)
@Import(RetryConfiguration.class)
@Documented
public @interface EnableRetry {

	/**
	 * Indicate whether subclass-based (CGLIB) proxies are to be created as opposed
	 * to standard Java interface-based proxies. The default is {@code false}.
	 *
	 * @return whether to proxy or not to proxy the class
	 */
	boolean proxyTargetClass() default false;

}

@Retryable注解, 标记的方法发生异常时会重试

• value 指定发生的异常进行重试
• include 与value一样,默认为空,当exclude同时为空时,所有异常都重试
• exclude 指定异常不重试,默认为空,当include同时为空,所有异常都重试
• maxAttemps 重试次数,默认3
• backoff 重试补充机制 默认是@Backoff()注解

@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).
	 * @return exception types 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()}.
	 * @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();

	/**
	 * 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 "";

}

@Backoff注解

• delay 延迟多久后重试
• multiplier 延迟的倍数

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Import(RetryConfiguration.class)
@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.
	 * @since 1.2
	 */
	String delayExpression() default "";

	/**
<<<<<<< HEAD
	 * An expression evaluating to the maximum wait (in milliseconds) between retries.
	 * If less than the {@link #delay()} then ignored.
=======
	 * 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.
>>>>>>> Fix @Backoff JavaDocs - maxDelay
	 * 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()} &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;

}

@Recover注解

• 当重试达到规定的次数后,被注解标记的方法将被调用, 可以在此方法中进行日志的记录等操作.(该方法的入参类型,返回值类型需要和重试方法保持一致)

@Target({ ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Import(RetryConfiguration.class)
@Documented
public @interface Recover {
}

参考资料:

https://blog.csdn.net/zzzgd_666/article/details/84377962