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>
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
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
