之前写了一些辅助工作相关的Spring Boot怎么使用AOP。这里继续正题，怎么减少Spring Boot 乐观锁加锁报错的情况（基本可以解决）。
1. 包依赖
spring-boot-starter-data-jpa， Spring Boot的JPA starter
h2， H2内存数据库
spring-boot-starter-test，Spring Boot的Junit测试starter
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
<version>1.2.6.RELEASE</version>
</dependency> <dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<version>1.4.188</version>
<scope>runtime</scope>
</dependency> <dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<version>1.2.6.RELEASE</version>
<scope>test</scope>
</dependency>
2. 如何在启用乐观锁？
我用的是JPA, 所以很简单，在实体类加一个字段，并注解＠Version。
@Entity
public class Account { //primary key, auto generated
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id; private String name; // enable optimistic locking version control
@Version
private int version; ／*omitted getter/setter, but required*／
}
3. 通过AOP实现对RetryOnOptimisticLockingFailureException的恢复
为了减少对代码的侵入，对之前的AOP例子进行少许修改：
- 自定义一个注解，用来标注需要恢复这个错误的接口
@Retention(RetentionPolicy.RUNTIME)
public @interface RetryOnOptimisticLockingFailure { }
- 切入点表达式使用注解，不再使用execution
@Pointcut("@annotation(RetryOnOptimisticLockingFailure)")
public void retryOnOptFailure() {
// pointcut mark
}
@Around("retryOnOptFailure()")
public Object doConcurrentOperation(ProceedingJoinPoint pjp) throws Throwable {
int numAttempts = 0;
do {
numAttempts++;
try {
return pjp.proceed();
} catch (OptimisticLockingFailureException ex) {
if (numAttempts > maxRetries) {
//log failure information, and throw exception
throw ex;
}else{
//log failure information for audit/reference
//will try recovery
}
}
} while (numAttempts <= this.maxRetries);
return null;
}
- 在需要对错误进行恢复的RESTFul接口加上恢复标签
至于为什么一定是要在RESTFul接口上加，而不是其他地方（例如service层），是因为Spring Boot的事务管理的上下文是从resource层开始建立的，在service层恢复是无效的，因为数据库的操作依然是在之前失败的事务里，之后再细说吧。
@RestController
@RequestMapping("/account")
public class AccountResource { @Autowired
private AccountService accountService; @RequestMapping(value = "/{id}/{name}", method = RequestMethod.PUT)
@ResponseBody
@RetryOnOptimisticLockingFailure
public void updateName(@PathVariable Integer id, @PathVariable String name) {
accountService.updateName(id, name);
}
}
4. 测试用例
@Test
public void testUpdate() {
new Thread(() -> this.client.put(base + "/1/llt-2", null)).start();
new Thread(() -> this.client.put(base + "/1/llt-3", null)).start(); try {
//waiting for execution result of service
Thread.sleep(5000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
5. 测试一下效果如何
- 没有在AccountResource的updateName方法加@RetryOnOptimisticLockingFailure：
Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.orm.ObjectOptimisticLockingFailureException: Object of class [com.leolztang.sb.aop.model.Account] with identifier [1]: optimistic locking failed; nested exception is org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [com.leolztang.sb.aop.model.Account#1]] with root cause org.hibernate.StaleObjectStateException: Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect) : [com.leolztang.sb.aop.model.Account#1]
at org.hibernate.persister.entity.AbstractEntityPersister.check(AbstractEntityPersister.java:2541)
at org.hibernate.persister.entity.AbstractEntityPersister.update(AbstractEntityPersister.java:3285)
- 在AccountResource的updateName方法加@RetryOnOptimisticLockingFailure：
Original:name=[llz-1],version=[0],New:name=[llt-2],version=[1]
Original:name=[llt-2],version=[1],New:name=[llt-3],version=[2]