MyBatis运行原理讲解

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration >
 <properties resource="jdbc.properties" />
 <!-- 设置信息元素
  会修改MyBatis在运行时的行为方式 -->
  <settings>  
                <!-- 全局映射器启用缓存 -->  
        <setting name="cacheEnabled" value="true" />  
                <!-- 查询时，关闭关联对象及时加载以提高性能 -->  
        <setting name="lazyLoadingEnabled" value="true" />  
                <!-- 设置关联对象加载的形态，此处为按需加载字段(加载字段由SQL指定)，不会加载关联表的所有字段，以提高性能 -->  
        <setting name="aggressiveLazyLoading" value="false" />  
                <!-- 对于未知的SQL查询，允许返回不同的结果集以达到通用的效果 -->  
        <setting name="multipleResultSetsEnabled" value="true" />  
                <!-- 允许使用列标签代替列名 -->  
        <setting name="useColumnLabel" value="true" />  
                <!-- 允许使用自定义的主键值(比如由程序生成的UUID 32位编码作为键值)，数据表的PK生成策略将被覆盖 -->  
        <setting name="useGeneratedKeys" value="true" />  
                <!-- 给予被嵌套的resultMap以字段-属性的映射支持 -->  
        <setting name="autoMappingBehavior" value="FULL" />  
                <!-- 对于批量更新操作缓存SQL以提高性能  -->  
        <setting name="defaultExecutorType" value="BATCH" />  
                <!-- 数据库超过25000秒仍未响应则超时 -->  
        <setting name="defaultStatementTimeout" value="25000" />  
    </settings>  
    
 <!-- 
 第一种写法
 类型别名是为Java类型命名一个短的名字。它只和XML配置有关，只用来减少类完全限定名的多余部分
  <typeAliases>
  <typeAlias alias="Person" type="com.msun.daomain.Person"/>
</typeAliases>
-->
<!-- 第二种写法  配合注解使用,在该包com.msun.daomain下使用注解@Alias("person")
指定一个包中所有类的别名-->
<typeAliases>
  <package name="com.msun.daomain"/>
</typeAliases>
<!--
development:开发模式
work:工作模式 
 -->
  <environments default="development" >
    <environment id="development" >
      <transactionManager type="JDBC" />
      
      <!-- JDBC连接对象的数据源连接池的实现，用来避免创建新的连接实例时必要的初始
      连接和认证时间。这是一种当前Web应用程序用来快速响应请求很流行的方法。 -->
      <dataSource type="POOLED" >
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${username}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
</configuration>

@Override
public void insertUser(JSONObject user) {
SqlSession session = null;
try {

//根据 JDBC 规范建立与数据库的连接；
session = sqlSessionFactory.openSession();

//通过反射打通 Java 对象与数据库参数交互之间相互转化关系
UserMapper mapper = session.getMapper(UserMapper.class);
mapper.insertUser(parasJson(user));
session.commit();
} finally {
session.close();
}
}

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    //如果不存在这个mapper，则直接抛出异常
    if (!knownMappers.contains(type))
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    try {
      //返回代理类
      return MapperProxy.newMapperProxy(type, sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

public interface UserMapper {
@Select(value="select * from user where id = #{id}")
public User findUserById(int id);

@Select(value="select * from user where username = #{username} and password = #{password}")
public User login(User user);

@Insert(value="insert into user (id,username,phone,email,password) values(#{id},#{username},#{phone},#{email},#{password})")
public void insertUser(User user);

@Select(value="select * from user where nickname = #{nickname} and email = #{email}")
public User findUserByNameAndEmail(User user);
}

public class SqlSessionUtils {

/**
* SqlSessionFactory对象可以看成DataSource（数据库连接池）
* 在应用执行期间，应该只创建一次，建议使用单例模式  
*/
private static SqlSessionFactory factory=null;
public static SqlSessionFactory getSessionFactory(){

if(factory==null){
synchronized (SqlSessionUtils.class) {
if(factory==null){
try {

//1.创建配置文件的输入流
String resource = "mybatis.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);

//2.创建SqlSessionFactory
factory=new SqlSessionFactoryBuilder().build(inputStream);

//添加映射器类（注解方式），避免了对xml文件的依赖
factory.getConfiguration().addMapper(MyLotteryMapper.class);
factory.getConfiguration().addMapper(LotteryMapper.class);
factory.getConfiguration().addMapper(UserMapper.class);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
}
}
return factory;
}
}

public interface UserMapper { @Select(value="select * from user where id = #{id}") public User findUserById(int id); @Select(value="select * from user where username = #{username} and password = #{password}") public User login(User user); @Insert(value="insert into user (id,username,phone,email,password) values(#{id},#{username},#{phone},#{email},#{password})") public void insertUser(User user); @Select(value="select * from user where nickname = #{nickname} and email = #{email}") public User findUserByNameAndEmail(User user); }

public void addMapper(Class<?> type) { //因为Java的动态代理只能实现接口，因而在注册mapper时也只能注册接口 if (type.isInterface()) { //如果已经注册过了，则抛出异常，而不是覆盖 if (knownMappers.contains(type)) { throw new BindingException("Type " + type + " is already known to the MapperRegistry."); } boolean loadCompleted = false; try { //先将这个mapper添加到mybatis中，如果加载过程中出现异常需要再将这个mapper从mybatis中删除 knownMappers.add(type); // It's important that the type is added before the parser is run // otherwise the binding may automatically be attempted by the // mapper parser. If the type is already known, it won't try. //下面两行代码其实做了很多的事，由于涉及的东西较多，在此不做过多的描述，留待以后专门进行介绍 MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type); parser.parse(); loadCompleted = true; } finally { if (!loadCompleted) { knownMappers.remove(type); } } } }