Spring Data Jpa执行流程分析

本文章采用Customer类举例说明

Customer：

@Entity
@Table(name = "cst_customer")
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Customer {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "cust_id")
    private Long custId;
    @Column(name = "cust_name")
    private String custName;
    @Column(name = "cust_source")
    private String custSource;

    @Column(name = "cust_industry")
    private String custIndustry;
    @Column(name = "cust_level")
    private String custLevel;
    @Column(name = "cust_address")
    private String custAddress;
    @Column(name = "cust_phone")
    private String custPhone;

}

CustomerDao：

public interface CustomerDao extends JpaRepository<Customer, Long>, JpaSpecificationExecutor<Customer> {
}

动态代理有4个角色，在Spring Data Jpa中分别为：

• 抽象角色：JpaRepository, JpaSpecificationExecutor
• 真实角色：SimpleJpaRepository
• 调用处理器：JdkDynamicAopProxy
• 代理角色：被注入到CustomerDao接口

其中代理角色和真实角色都实现了抽象角色

测试：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = "classpath:spring-dao.xml")
public class MyTest {
    @Autowired
    private CustomerDao customerDao;
    @Test
    public void findOne() {
        Customer customer = customerDao.findOne(31L);
        System.out.println(customer);
    }
}

在输出语句地方打个断点，可以看到customerDao被注入的是个SimpleJpaRepository的动态代理对象：

继续执行，会执行到JdkDynamicAopProxy（可以看到该类继承了InvocationHandler）：

final class JdkDynamicAopProxy implements AopProxy, InvocationHandler, Serializable {
    ...
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		...
    }
    ...
}

接着会调用SimpleJpaRepository中的findOne方法：

public class SimpleJpaRepository<T, ID extends Serializable> implements JpaRepository<T, ID>, JpaSpecificationExecutor<T> {
    ...
    public T findOne(ID id) {
        Assert.notNull(id, "The given id must not be null!");
        Class<T> domainType = this.getDomainClass();
        if (this.metadata == null) {
            return this.em.find(domainType, id);
        } else {
            LockModeType type = this.metadata.getLockModeType();
            Map<String, Object> hints = this.getQueryHints();
            return type == null ? this.em.find(domainType, id, hints) : this.em.find(domainType, id, type, hints);
        }
    }
    ...
}

最后findOne方法中再调用实体管理器的find方法。