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-easysrcmainjavacom
regmapperUserMapper.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。