spring mybatis 之MapperFactoryBean-优快云博客

本文链接：https://blog.youkuaiyun.com/hepei120/article/details/78209665

mybatis 为什么只要写接口而不用去实现这是因为spring利用JDK动态代理实现我们定义的接口

下面先看demo再分析
实体类User

package com.eroadsf.springdemo.mybatis.entity;

public class User {
    private Integer id;
    private String name;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

UserMapper

package com.eroadsf.springdemo.mybatis.mapper;

import java.util.List;

import com.eroadsf.springdemo.mybatis.entity.User;

public interface UserMapper {
    public List<User> selectAll();

}

User.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
PUBLIC "-//ibatis.apache.org//DTD Mapper 3.0//EN"
"http://ibatis.apache.org/dtd/ibatis-3-mapper.dtd">
<mapper namespace="com.eroadsf.springdemo.mybatis.mapper.UserMapper">

    <select id="selectAll" resultType="User">
        <![CDATA[ 
        SELECT * FROM user
        ]]>
    </select>


</mapper>

spring-mybatis.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
      http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
      http://www.springframework.org/schema/context 
      http://www.springframework.org/schema/context/spring-context-4.0.xsd
      http://www.springframework.org/schema/aop
      http://www.springframework.org/schema/aop/spring-aop-4.0.xsd">

    <context:component-scan base-package="com.eroadsf.springdemo.mybatis" />

    <!-- 读入properties资源文件 -->
    <context:property-placeholder location="classpath:db.properties" />
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"
        destroy-method="close">
        <property name="driverClassName" value="${jdbc.driver}" />
        <property name="url" value="${jdbc.url}" />
        <property name="username" value="${jdbc.username}" />
        <property name="password" value="${jdbc.password}" />
    </bean>

    <bean id="sessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="mapperLocations" value="classpath*:mybatis/mapper/**/*.xml" />
        <property name="typeAliasesPackage" value="com.eroadsf.springdemo.mybatis.entity" />
    </bean>

    <bean id="userMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
        <property name="mapperInterface"
            value="com.eroadsf.springdemo.mybatis.mapper.UserMapper" />
        <property name="sqlSessionFactory" ref="sessionFactory" />
    </bean>

</beans>

测试类

import java.util.List;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.eroadsf.springdemo.mybatis.entity.User;
import com.eroadsf.springdemo.mybatis.mapper.UserMapper;

/**
 * 
 * @author hepei
 * @date 2017年10月11日 下午11:12:54
 */
public class MybatisTest {
    @SuppressWarnings("deprecation")
    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("spring-mybatis.xml");
        UserMapper mapper = ctx.getBean("userMapper", UserMapper.class);
        List<User> userlist = mapper.selectAll();
        for(User u:userlist){
            System.out.println(u.getName());
        }
    }

}

结果：
唐骏
李开复
柳传志
唐骏
李开复
柳传志

下面在分析spring怎么利用动态代理帮我实现调用xml的sql
入口就是org.mybatis.spring.mapper.MapperFactoryBean

MapperFactoryBean继承了SqlSessionDaoSupport类，SqlSessionDaoSupport类继承DaoSupport抽象类，DaoSupport抽象类实现了InitializingBean接口，因此实例个MapperFactoryBean的时候，都会调用InitializingBean接口的afterPropertiesSet方法。

DaoSupport 类

@Override
    public final void afterPropertiesSet() throws IllegalArgumentException, BeanInitializationException {
        // Let abstract subclasses check their configuration.
        checkDaoConfig();

        // Let concrete implementations initialize themselves.
        try {
            initDao();
        }
        catch (Exception ex) {
            throw new BeanInitializationException("Initialization of DAO failed", ex);
        }
    }

MapperFactoryBean 重写了checkDaoConfig方法

@Override
  protected void checkDaoConfig() {
    super.checkDaoConfig();

    notNull(this.mapperInterface, "Property 'mapperInterface' is required");

    Configuration configuration = getSqlSession().getConfiguration();
    //configuration是否包含mapperInterface,如果没就加入
    if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
      try {
        configuration.addMapper(this.mapperInterface);
      } catch (Throwable t) {
        logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", t);
        throw new IllegalArgumentException(t);
      } finally {
        ErrorContext.instance().reset();
      }
    }
  }

实现了FactoryBean,在getBean的时候其实调用的是getObject方法

 public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }

这里的
这里的SqlSession是SqlSessionTemplate，SqlSessionTemplate的getMapper方法：

SqlSessionTemplate

public <T> T getMapper(Class<T> type) {
    return getConfiguration().getMapper(type, this);
  }

Configuration

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    return mapperRegistry.getMapper(type, sqlSession);
  }

MapperRegistry

 public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
    if (mapperProxyFactory == null)
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

MapperProxyFactory构造MapperProxy：

 protected T newInstance(MapperProxy<T> mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

 public T newInstance(SqlSession sqlSession) {
    final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

MapperProxy 实现了InvocationHandler，jdk动态代理

public class MapperProxy<T> implements InvocationHandler, Serializable {

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache;

  public MapperProxy(SqlSession sqlSession, Class<T> mapperInterface, Map<Method, MapperMethod> methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
      return method.invoke(this, args);
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }

MapperMethod

public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    if (SqlCommandType.INSERT == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.insert(command.getName(), param));
    } else if (SqlCommandType.UPDATE == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.update(command.getName(), param));
    } else if (SqlCommandType.DELETE == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.delete(command.getName(), param));
    } else if (SqlCommandType.SELECT == command.getType()) {
      if (method.returnsVoid() && method.hasResultHandler()) {
        executeWithResultHandler(sqlSession, args);
        result = null;
      } else if (method.returnsMany()) {
        result = executeForMany(sqlSession, args);
      } else if (method.returnsMap()) {
        result = executeForMap(sqlSession, args);
      } else {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = sqlSession.selectOne(command.getName(), param);
      }
    } else {
      throw new BindingException("Unknown execution method for: " + command.getName());
    }
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
      throw new BindingException("Mapper method '" + command.getName() 
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
    List<E> result;
    Object param = method.convertArgsToSqlCommandParam(args);
    if (method.hasRowBounds()) {
      RowBounds rowBounds = method.extractRowBounds(args);
      result = sqlSession.<E>selectList(command.getName(), param, rowBounds);
    } else {
      result = sqlSession.<E>selectList(command.getName(), param);
    }
    // issue #510 Collections & arrays support
    if (!method.getReturnType().isAssignableFrom(result.getClass())) {
      if (method.getReturnType().isArray()) {
        return convertToArray(result);
      } else {
        return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
      }
    }
    return result;
  }