1, Environment construction
- Add spring retry dependency. Spring retry uses AOP implementation, so you also need to add AOP package
<!-- SpringRetry -->
<dependency>
<groupId>org.springframework.retry</groupId>
<artifactId>spring-retry</artifactId>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-aspects</artifactId>
</dependency>
- Official documents
2, RetryTemplate
2.1 RetryTemplate
- RetryTemplate encapsulates the basic operations of Retry
- org.springframework.retry.support.RetryTemplate
- Listening, fallback policy and retry policy can be specified in RetryTemplate
- Just use the normal new RetryTemplate()
2.2 RetryListener
- RetryListener specifies the callback when an error occurs during execution
- org.springframework.retry.RetryListener
package org.springframework.retry;
public interface RetryListener {
/**
* Called at the beginning of task execution, only once
*/
<T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback);
/**
* Called at the end of task execution (including retry), only once
*/
<T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable);
/**
* Callback on error
*/
<T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable);
}
- Specify in RetryTemplate after configuration
2.3 fallback strategy
2.3.1 FixedBackOffPolicy
- How long is the delay to continue the call when an error occurs
FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy();
fixedBackOffPolicy.setBackOffPeriod(1000L);
retryTemplate.setBackOffPolicy(fixedBackOffPolicy);
- Specify in RetryTemplate after configuration
2.3.2 ExponentialBackOffPolicy
- When an error occurs, it is delayed by the specified delay time for the first time and then by the index
// Exponential fallback (seconds), the first fallback is 1s, the second fallback is 2s, the third is 4 seconds, and the fourth is 8 seconds
ExponentialBackOffPolicy exponentialBackOffPolicy = new ExponentialBackOffPolicy();
exponentialBackOffPolicy.setInitialInterval(1000L);
exponentialBackOffPolicy.setMultiplier(2);
retryTemplate.setBackOffPolicy(exponentialBackOffPolicy);
- Specify in RetryTemplate after configuration
2.4 retry strategy
- The retry policy mainly specifies the number of retries when an error occurs
// Retry policy
SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy();
retryPolicy.setMaxAttempts(5);
retryTemplate.setRetryPolicy(retryPolicy);
- Specify in RetryTemplate after configuration
2.5 RetryCallback
- RetryCallback is retrytemplate Callback executed when execute
- public final <T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback) throws E
2.6 core usage
- RetryTemplate can be used for simple use
- Configure retryTemplate
- Specifies that the fallback policy is ExponentialBackOffPolicy
- Specify the retry policy as SimpleRetryPolicy
- Specifies the listener 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 {
/**
* Inject retryTemplate
*/
@Bean
public RetryTemplate retryTemplate() {
RetryTemplate retryTemplate = new RetryTemplate();
///Fallback fixed time (seconds)
/* FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy();
fixedBackOffPolicy.setBackOffPeriod(1000L);
retryTemplate.setBackOffPolicy(fixedBackOffPolicy);*/
// Exponential fallback (seconds), 1s for the first time and 2s for the second time
ExponentialBackOffPolicy exponentialBackOffPolicy = new ExponentialBackOffPolicy();
exponentialBackOffPolicy.setInitialInterval(1000L);
exponentialBackOffPolicy.setMultiplier(2);
retryTemplate.setBackOffPolicy(exponentialBackOffPolicy);
// Retry policy
SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy();
retryPolicy.setMaxAttempts(5);
retryTemplate.setRetryPolicy(retryPolicy);
// Set the listener, and open and close are executed once at startup and end respectively
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;
}
}
- Inject RetryTemplate into controller or service
@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 -> {
// Business code
// ....
// Simulate throwing an exception
++count;
throw new RuntimeException("Throw exception");
});
} catch (RuntimeException e) {
System.out.println("Exception");
}
return "retry = " + count;
}
}
- Access the retry interface and observe the log output
18:27:20.648 - http-nio-8888-exec-1 - open
18:27:20.649 - http-nio-8888-exec-1 - retryTemplate.execute implement
18:27:20.649 - http-nio-8888-exec-1 - onError
18:27:21.658 - http-nio-8888-exec-1 - retryTemplate.execute implement
18:27:21.658 - http-nio-8888-exec-1 - onError
18:27:23.670 - http-nio-8888-exec-1 - retryTemplate.execute implement
18:27:23.670 - http-nio-8888-exec-1 - onError
18:27:27.679 - http-nio-8888-exec-1 - retryTemplate.execute implement
18:27:27.679 - http-nio-8888-exec-1 - onError
18:27:35.681 - http-nio-8888-exec-1 - retryTemplate.execute implement
18:27:35.681 - http-nio-8888-exec-1 - onError
18:27:35.681 - http-nio-8888-exec-1 - close
3, EnableRetry
- @EnableRetry enables retry. When specified on the class, the method will execute by default and retry three times
- Define the service, open the @ EnableRetry annotation and specify @ Retryable to retry. Refer to the following section
import org.springframework.retry.annotation.Retryable;
public interface RetryService {
/**
* Retry method call
*/
@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("Method call..");
throw new RuntimeException("Manual exception");
}
}
- Inject service into controller
@RequestMapping("/retryAnnotation")
public Object retryAnnotation() {
retryService.retryServiceCall();
return "retryAnnotation";
}
- Will retry by default
18:46:48.721 - http-nio-8888-exec-1 - Method call..
18:46:49.724 - http-nio-8888-exec-1 - Method call..
18:46:50.730 - http-nio-8888-exec-1 - Method call..
java.lang.RuntimeException: Manual exception
4, Retryable
- Annotation on the method that needs to be retried
- There are several properties
- Retryable annotation parameter
- value: specify the exception to retry
- include: like value, it is empty by default. When exclude is also empty, all exceptions will be retried
- exclude: Specifies that the exception will not be retried. It is empty by default. When include is also empty, all exceptions will be retried
- Maxattempts: number of retries. The default is 3
- backoff: retry compensation mechanism, not available by default
- @Backoff annotation retry compensation strategy
- When the parameter is not set, the FixedBackOffPolicy (specify the waiting time) is used by default, and the retry wait is 1000ms
- Set delay and use FixedBackOffPolicy (specify that the retry wait is evenly distributed between the two values when delay and maxDealy are set)
- Set delay, maxDealy and multiplier, and use ExponentialBackOffPolicy (implementation of exponential retry interval). Multiplier specifies the delay multiple. For example, delay=5000L, multiplier=2, then the first retry is 5 seconds, the second is 10 seconds, and the third is 20 seconds
@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;
}
- On the method to be retried, configure the corresponding retry times, the exception type of the retry exception, set the fallback delay time, the retry policy, and the method listening name
@Component
public class PlatformClassService {
@Retryable(
// Retry the exception type of the exception
value = {Exception.class},
// max retries
maxAttempts = 5,
// Set fallback delay time
backoff = @Backoff(delay = 500),
// Configure callback method name
listeners = "retryListener"
)
public void call() {
System.out.println("call...");
throw new RuntimeException("Manual exception");
}
}
// The initial delay is 2 seconds, and then the acceptance is 1.5 times delayed for retry. The total number of retries is 4
@Retryable(value = {Exception.class}, maxAttempts = 4, backoff = @Backoff(delay = 2000L, multiplier = 1.5))
- The listening method is configured in the configuration class
/**
* Annotation call
*/
@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);
// The subsequent call returns true to continue execution
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);
}
};
}
- Call service
@RestController
public class SpringRetryController {
@Resource
private PlatformClassService platformClassService;
@RequestMapping("/retryPlatformCall")
public Object retryPlatformCall() {
try {
platformClassService.call();
} catch (Exception e) {
return "Attempt to call failed";
}
return "retryPlatformCall";
}
}
- Call result
