一张图带你看懂原始dao与SQL动态代理开发的区别-Mybatis

//转载请注明出处：https://www.cnblogs.com/nreg/p/11156167.html

1.项目结构区别：

2.开发区别：

注：其中原始dao开发的实现类UserDaoImpl 与动态代理开发的工具类UserService的第16行-第27行代码可以提炼出来，

每个逻辑方法里都要注入这6行代码，会有些繁琐，因此需要提炼出来作为一个工厂类，对外提供Sqlsession会话。

3.工厂类：Factory

 public class Factory {
     private final static Class<Factory> lock = Factory.class;
     private static SqlSessionFactory sqlSessionFactory = null;
     private Factory() {}

     public static SqlSessionFactory getSqlSessionFactory() {
         synchronized (lock) {
             if (sqlSessionFactory != null) {
                 return sqlSessionFactory;
             }
             //加载核心配置文件
             String resource = "mybatis-config.xml";
             InputStream inputStream;
             try {
                 inputStream = Resources.getResourceAsStream(resource);
                 //创建SqlsessionFactory工厂
                 sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
             } catch (IOException e) {
                 e.printStackTrace();
                 return null;
             }
             //对外提供一个工厂
             return sqlSessionFactory;
         }
     }

     //对外提供一个Sqlsession会话
     public static SqlSession getSession() {
         if (sqlSessionFactory == null) {
             getSqlSessionFactory();
         }
         return sqlSessionFactory.openSession();
     }
 }

工厂类使用示例：

4.Mybatis的核心配置文件：mybatis-config.xml

 <?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"></properties>

     <!--environments元素：配置Mybatis的运行环境-->
     <!--可配置多套运行环境，将SQL映射到多个不同的数据库上，但必须通过default属性指定默认运行环境-->
     <environments default="development"> <!--default属性指定默认运行环境的id-->
         <environment id="development">   <!-- 第一套运行环境的id-->
             <transactionManager type="JDBC"></transactionManager> <!--事务管理器配置-->
             <dataSource type="POOLED">   <!--数据源(连接池)配置-->
                 <property name="driver" value="${jdbc.driver}"/>
                 <property name="url" value="${jdbc.url}"/>
                 <property name="username" value="${jdbc.username}"/>
                 <property name="password" value="${jdbc.password}"/>
             </dataSource>
         </environment>
     </environments>

     <!--mappers元素：配置mapper映射器的xml映射文件 以动态代理开发为例，原始dao开发配置方法相同-->
     <mappers>
         <!--方式一：使用resource配置映射文件-->
         <mapper resource="com/nreg/mapper/UserMapper.xml"></mapper>
         <!--方式二：使用url配置映射文件-->
         <mapper url="D:\Mybatis-agency-easy\src\main\java\com\nreg\mapper\UserMapper.xml"></mapper>
         <!--方式三：多个映射器的使用：开启扫描-->
         <package name="com.nreg.mapper"/>
     </mappers>
 </configuration>

5.外部属性文件：jdbc

 jdbc.driver=com.mysql.jdbc.Driver
 jdbc.url=jdbc:mysql://localhost:3306/crud?useSSL=false&serverTimezone=UTC&characterEncoding=utf-8
 jdbc.username=root
 jdbc.password=123456

6.日志文件：log4j

 ### 设置Logger输出级别和输出目的地 ### debug更详细,如果把debug改为info，则打印出的表数据遇到字符串就不显示，此外还有log4j.log文件
 log4j.rootLogger=debug,stdout

 ### 把日志信息输出到控制台 ###
 log4j.appender.stdout=org.apache.log4j.ConsoleAppender
 #log4j.appender.stdout.Target=System.err
 log4j.appender.stdout.layout=org.apache.log4j.SimpleLayout 

 ### 把日志信息输出到文件：log4j.log ###
 log4j.appender.logfile=org.apache.log4j.FileAppender
 log4j.appender.logfile.File=log4j.log
 log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
 log4j.appender.logfile.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %F %p %m%n

 ###显示SQL语句部分 ###
 #第一行：xml映射文件所在包
 log4j.logger.com.nreg.sqlMap=DEBUG
 log4j.logger.java.sql.Connection=DEBUG
 log4j.logger.java.sql.Statement=DEBUG
 log4j.logger.java.sql.PreparedStatement=DEBUG
 log4j.logger.java.sql.ResultSet=DEBUG

7.开发用crud模板：

1).接口：

     //增
     boolean addUser(User user);
     //删
     boolean deleteUserById(int id);
     //改
     boolean updateUserById(User user);
     //查:按id查一个
     User getUserById(int id);
     //查:查所有
     List<User> getUser();

2).xml映射文件：

    <!--增-->
    <insert id="addUser" parameterType="com.nreg.bean.User" useGeneratedKeys="true" keyProperty="id">
        insert into user values(null,#{username},#{password})
    </insert>

    <!--删-->
    <delete id="deleteUserById" parameterType="int">
        delete from user where id = #{id}
    </delete>

    <!--改-->
    <update id="updateUserById" parameterType="com.nreg.bean.User">
        update user set username = #{username},password = #{password} where id=#{id}
    </update>

    <!--查:按id查-->
    <select id="getUserById" parameterType="int" resultType="com.nreg.bean.User">
        select * from user where 1=1 and id = #{id}<!--注：1=1 and：用于防止后面条件不成立造成SQL语句错误-->
    </select>

    <!--查:查所有-->
    <select id="getUser" resultType="com.nreg.bean.User">
        select * from user
    </select>

3).动态代理开发：UserService工具类：

 public class UserService {

     SqlSession sqlsession=null;
     //增
     public boolean addUser(User user) {
         try {
             //1.通过工厂获取会话
             sqlsession= Factory.getSession();
             //2.从会话中获取接口的代理对象
             UserMapper userMapper=sqlsession.getMapper(UserMapper.class);
             //3.通过代理对象操作数据库
             userMapper.addUser(user);
             //提交事务
             sqlsession.commit();
             return true;
         } catch (Exception e) {
             //回滚
             if(sqlsession !=null){
                 sqlsession.rollback();
             }
             return false;
         }finally{
             //关闭连接,释放资源
             if(sqlsession!=null){
                 sqlsession.close();
             }
         }
     }

     //删
     public boolean deleteUserById(int id) {
         try {
             sqlsession= Factory.getSession();
             UserMapper userMapper=sqlsession.getMapper(UserMapper.class);
             boolean tf=userMapper.deleteUserById(id);
             sqlsession.commit();
             return tf;
         } catch (Exception e) {
             if(sqlsession!=null){
                 sqlsession.rollback();
             }
             return false;
         }finally{
             if(sqlsession!=null){
                 sqlsession.close();
             }
         }
     }

     //改
     public boolean updateUserById(User user) {

         try {
             sqlsession= Factory.getSession();
             UserMapper userMapper=sqlsession.getMapper(UserMapper.class);
             userMapper.updateUserById(user);
             sqlsession.commit();
             return true;
         } catch (Exception e) {
             if(sqlsession !=null){
                 sqlsession.rollback();
             }
             return false;
         }finally{
             if(sqlsession !=null){
                 sqlsession.close();
             }
         }
     }

     //查:按id查一个
     public User getUserById(int id) {

         try {
             sqlsession= Factory.getSession();
             UserMapper userMapper=sqlsession.getMapper(UserMapper.class);
             User user = userMapper.getUserById(id);
             return user;

         } catch (Exception e) {
             if(sqlsession!=null){
                 sqlsession.rollback();
             }
             e.printStackTrace();
             return null;
         }finally{
             if(sqlsession !=null){
                 sqlsession.close();
             }
         }
     }

     //查:查所有
     public List<User> getUser() {

         try {
             sqlsession = Factory.getSession();
             List<User> list = null;
             UserMapper userMapper=sqlsession.getMapper(UserMapper.class);
             list = userMapper.getUser();
             return list;
         } catch (Exception e) {
             if(sqlsession!=null){
                 sqlsession.rollback();
             }
             return null;
         }finally{
             if(sqlsession !=null){
                 sqlsession.close();
             }
         }
     }
 }

4).原始dao开发：UserDaoImpl实现类：

 public class UserDaoImpl implements UserDao {

     SqlSession sqlsession = null;
     //增：
     @Override
     public boolean addUser(User user) {
         try {
             //1.通过工厂获取会话
             sqlsession = Factory.getSession();
             //2.通过会话操作数据库
             sqlsession.insert("addUser", user);
             //提交事务:增删改都需要提交事务
             sqlsession.commit();
             return true;
         } catch (Exception e) {
             //回滚
             if (sqlsession != null) {
                 sqlsession.rollback();
             }
             return false;
         } finally {
             //关闭连接,释放资源
             if (sqlsession != null) {
                 sqlsession.close();
             }
         }
     }

     //删
     @Override
     public boolean deleteUserById(int id) {
         try {
             //1.通过工厂获取会话
             sqlsession = Factory.getSession();
             //2.通过会话操作数据库
             sqlsession.delete("deleteUserById",id);
             //3.提交事务
             sqlsession.commit();
             return true;
         } catch (Exception e) {
             if (sqlsession != null) {
                 //回滚
                 sqlsession.rollback();
             }
             return false;
         } finally {
             if (sqlsession != null) {
                 //关闭连接，释放资源
                 sqlsession.close();
             }
         }
     }

     //改：
     @Override
     public boolean updateUserById(User user) {
         try {
             sqlsession = Factory.getSession();
             sqlsession.update("updateUserById", user);
             sqlsession.commit();
             return true;
         } catch (Exception e) {
             if (sqlsession != null) {
                 sqlsession.rollback();
             }
             return false;
         } finally {
             if (sqlsession != null) {
                 sqlsession.close();
             }
         }
     }

     //查：按id查
     @Override
     public User getUserById(int id) {
         try {
             sqlsession = Factory.getSession();
             User user = sqlsession.selectOne("getUserById",id);
             return user;
         } catch (Exception e) {
             if (sqlsession != null) {
                 sqlsession.rollback();
             }
             return null;
         } finally {
             if (sqlsession != null) {
                 sqlsession.close();
             }
         }
     }

     //查：查所有
     @Override
     public List<User> getUser() {
         try {
             sqlsession = Factory.getSession();
             List<User> list = sqlsession.selectList("getUser");
             return list;
         } catch (Exception e) {
             if (sqlsession != null) {
                 sqlsession.rollback();
             }
             return null;
         } finally {
             if (sqlsession != null) {
                 sqlsession.close();
             }
         }
     }
 }

结。