Spring Boot 乐观锁加锁失败 - 使用AOP恢复错误

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]

6. 完整代码

http://files.cnblogs.com/files/leolztang/sb.aop-v2.tar.gz