【Spring Data JPA 系列】09、深入理解原理

我会带着你远行 2024-03-27 13:35 37阅读 0赞

## 10、原理 ##

### 10.1、Repository原理 ###

核心机制：**动态代理**：

1.  JdkDynamicAopProxy—invoke

*  调用 JPA的Repository统一实现
    
     *  SimpleJpaRepository
        
        ![format_png][]
    
     *  就是去通过JPA的API完成持久化操作
    
    ![format_png 1][]

手写代码进行测试：

源码分析：

package com.yykk.sourcecode;
     
     import com.yykk.config.SpringDataJPAConfig;
     import com.yykk.repositories.CustomerRepository;
     import org.springframework.context.annotation.AnnotationConfigApplicationContext;
     import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
     
     import javax.persistence.EntityManager;
     import java.lang.reflect.ParameterizedType;
     import java.lang.reflect.Proxy;
     import java.lang.reflect.Type;
     
     public class SourceCode {
         public static void main(String[] args) throws ClassNotFoundException {
             // spring上下文  spring容器 --- ioc加载过程：创建所有的bean，报错repository的Bean
             AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(SpringDataJPAConfig.class);
     
             //CustomerRepository repository = context.getBean(CustomerRepository.class);
     
             //System.out.println(repository.getClass()); // jdk 动态代理
     
             //Optional<Customer> byId = repository.findById(7L);
     
             //System.out.println(byId.get());
     
             // 获得entityManager
             LocalContainerEntityManagerFactoryBean entityManagerFactoryBean = context.getBean(LocalContainerEntityManagerFactoryBean.class);
             EntityManager nativeEntityManager = entityManagerFactoryBean.createNativeEntityManager(null);
     
             // 获得当前接口的pojo类
             // getGenericInterfaces() 拿到当前接口的父接口 = PagingAndSortingRepository
             ParameterizedType parameterizedType = (ParameterizedType)CustomerRepository.class.getGenericInterfaces()[0];
             // 拿到接口的泛型 = <Customer,Long>
             Type type = parameterizedType.getActualTypeArguments()[0];
             Class clazz = Class.forName(type.getTypeName());
     
             CustomerRepository repository = (CustomerRepository) Proxy.newProxyInstance(
                     CustomerRepository.class.getClassLoader(),
                     new Class[]{CustomerRepository.class},
                     new MyJpaRepository(nativeEntityManager,clazz)
             );
             repository.findById(7L);
         }
     }
    复制代码

package com.yykk.sourcecode;
     
     import javax.persistence.EntityManager;
     import java.lang.reflect.InvocationHandler;
     import java.lang.reflect.Method;
     
     public class MyJpaRepository implements InvocationHandler {
     
         EntityManager entityManager;
         Class pojoClass;
     
         public MyJpaRepository(EntityManager entityManager, Class pojoClass) {
             this.entityManager = entityManager;
             this.pojoClass = pojoClass;
         }
     
         // method 当前调用的方法
         // args 当前调用方法的参数
         @Override
         public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
     
             // jpa的统一实现类
             MyJpaProxy myJpaProxy = new MyJpaProxy(entityManager, pojoClass);
             Method targetMethod = myJpaProxy.getClass().getMethod(method.getName(), method.getParameterTypes());
     
             return targetMethod.invoke(myJpaProxy,args);
         }
     }
    复制代码

package com.yykk.sourcecode;
     
     import org.springframework.data.domain.Page;
     import org.springframework.data.domain.Pageable;
     import org.springframework.data.domain.Sort;
     import org.springframework.data.repository.PagingAndSortingRepository;
     
     import javax.persistence.EntityManager;
     import java.util.Optional;
     
     public class MyJpaProxy implements PagingAndSortingRepository {
     
         EntityManager entityManager;
         Class pojoClass;
     
         public MyJpaProxy(EntityManager entityManager, Class pojoClass) {
             this.entityManager = entityManager;
             this.pojoClass = pojoClass;
         }
     
         @Override
         public Iterable findAll(Sort sort) {
             return null;
         }
     
         @Override
         public Page findAll(Pageable pageable) {
             return null;
         }
     
         @Override
         public Object save(Object entity) {
             return null;
         }
     
         @Override
         public Iterable saveAll(Iterable entities) {
             return null;
         }
     
         @Override
         public Optional findById(Object id) {
             // JPA
             return Optional.of(entityManager.find(pojoClass,id));
         }
     
         @Override
         public boolean existsById(Object o) {
             return false;
         }
     
         @Override
         public Iterable findAll() {
             return null;
         }
     
         @Override
         public Iterable findAllById(Iterable iterable) {
             return null;
         }
     
         @Override
         public long count() {
             return 0;
         }
     
         @Override
         public void deleteById(Object o) {
     
         }
     
         @Override
         public void delete(Object entity) {
     
         }
     
         @Override
         public void deleteAllById(Iterable iterable) {
     
         }
     
         @Override
         public void deleteAll(Iterable entities) {
     
         }
     
         @Override
         public void deleteAll() {
     
         }
     }
    复制代码

package com.yykk.sourcecode;
     
     import com.yykk.config.SpringDataJPAConfig;
     import com.yykk.pojo.Customer;
     import com.yykk.repositories.CustomerRepository;
     import org.junit.Test;
     import org.junit.runner.RunWith;
     import org.springframework.beans.factory.annotation.Autowired;
     import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
     import org.springframework.test.context.ContextConfiguration;
     import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
     
     import java.util.Optional;
     
     @EnableJpaRepositories(basePackages = "com.yykk.repositories")
     @ContextConfiguration(classes = SpringDataJPAConfig.class)
     @RunWith(SpringJUnit4ClassRunner.class)
     public class SpringDataJpaSource {
     
         @Autowired
         CustomerRepository repository;
     
         @Test
         public void test_source() {
             Optional<Customer> id = repository.findById(7L);
             System.out.println(id.get());
         }
     }
    复制代码

![format_png 2][]

源码学习文章：

[www.dewafer.com/2016/05/09/…][www.dewafer.com_2016_05_09]

### 10.2、spring整合JPA原理 ###

1、spring怎么管理Repository（怎么创建的Repository的Bean）

1.  @EnableJpaRepositories(basePackages = "com.yykk.repositories")
2.  spring容器启动的时候ioc容器加载 ，根据 com.yykk.repositories 去创建bean

2、spring怎么将动态代理创建bean

Exceptioninthread"main"org.springframework.beans.factory.NoSuchBeanDefinitionException:No qualifying bean of type ' com.yykk.repositories.CustomerRepository' available
    复制代码

1.  没有找到bean，解决思路：
    
     *  应用层面：是不是配置不正确，配置正确，排除！
     *  底层层面：是不是spring底层扫描-排除。（Bean—>对象）

作者：Nakano\_May  
原文链接：https://juejin.cn/post/7196680499678740535

[format_png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/dc9fbfe1e8d24de99dfc280f9ee69014.png
[format_png 1]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/bc151582e63e441f947ab5ba91efbb87.png
[format_png 2]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/62761ec264d94146a90d1ede9306c65e.png
[www.dewafer.com_2016_05_09]: https://link.juejin.cn?target=http%3A%2F%2Fwww.dewafer.com%2F2016%2F05%2F09%2Freading-src-of-spring-data-jpa%2F