mybatis前因后果(二)mybatis的dao层实现

矫情吗；* 2022-11-03 01:00 161阅读 0赞

## 引言 ##

### 传统mybatis dao层实现 ###

UserDao接口

public interface UserDao { 
        List<User> findAll() throws IOException;
    }

UserDao实现

public class UserDaoImpl implements UserDao { 
        public List<User> findAll() throws IOException { 
            InputStream resourceAsStream = 
                        Resources.getResourceAsStream("SqlMapConfig.xml");
            SqlSessionFactory sqlSessionFactory = new 
                        SqlSessionFactoryBuilder().build(resourceAsStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();
            List<User> userList = sqlSession.selectList("userMapper.findAll");
            sqlSession.close();
            return userList;
        }
    }

UserServiceImpl

@Test
    public void findAll() throws IOException { 
        UserDao userDao = new UserDaoImpl();
        List<User> all = userDao.findAll();
        System.out.println(all);
    }

**总结：** 传统mybatis dao层实现基本与上篇文章的实现方法类似，都有非常多的重复代码，最为关键的是在service层调用dao层时，每次sql执行都会伴随着一个新dao对象的创建，这种情况会造成资源浪费，所以古圣先贤们给我提供新的方法，采用动态代理方式，此处采用的接口代理方式。

## mybatis 与dao接口代理 ##

下图给出的是mybatis 与dao接口实现动态代理的匹配规则  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1ZXNoYW5mZWl0aWFu_size_16_color_FFFFFF_t_70]  
匹配关系：  
**1) Mapper.xml文件中的namespace与mapper接口的全限定名相同**

**2) Mapper接口方法名和Mapper.xml中定义的每个statement的id相同**

**3) Mapper接口方法的输入参数类型和mapper.xml中定义的每个sql的parameterType的类型相同**

**4) Mapper接口方法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同**

### 案例 实现mybatis 与dao接口代理 ###

对于mybatis而言，需要关注的是需要了解相关的标签定义，下面将mybatis 与dao接口代理案例实现代码贴出。

1.  导入相关依赖
2.  dao接口

public interface UserDao { 
        public List<User> findAll() throws IOException;
        public List<User> findByCondition(User condition);
        public List<User> findByIds(List<Integer> ids);
        public void  saveUser(User user);
    }

1.  自定义类型转换器

public class DateTypeHandler extends BaseTypeHandler<Date> { 
    
        //将java类型转换成sql类型
        public void setNonNullParameter(PreparedStatement ps, int i, Date date, JdbcType jdbcType) throws SQLException, SQLException { 
            long time = date.getTime();
            ps.setLong(i,time);
        }
    
        //获取结果集合中有用的数据
        public Date getNullableResult(ResultSet rs, String columnName) throws SQLException { 
            long time = rs.getLong(columnName);
            Date date = new Date(time);
            return date;
        }
    
        public Date getNullableResult(ResultSet rs, int columnIndex) throws SQLException { 
            long time = rs.getLong(columnIndex);
            Date date = new Date(time);
            return date;
        }
    
        public Date getNullableResult(CallableStatement cs, int columnIndex) throws SQLException { 
            long time = cs.getLong(columnIndex);
            Date date = new Date(time);
            return date;
        }
    }

\*\* notes: 自定义类型转换处理器需要在sqlConfigMapper中注册。 \*\*

1.  实体类

public class User { 
        private int id;
        private String username;
        private String password;
        private Date birthday;
    
        public Date getBirthday() { 
            return birthday;
        }
    
        public void setBirthday(Date birthday) { 
            this.birthday = birthday;
        }
    
        public User(int id, String username, String password, Date birthday) { 
            this.id = id;
            this.username = username;
            this.password = password;
            this.birthday = birthday;
        }
    
        public User() { 
        }
    
        public User(int id, String username, String password) { 
            this.id = id;
            this.username = username;
            this.password = password;
        }
    
    
        public int getId() { 
            return id;
        }
    
        public void setId(int id) { 
            this.id = id;
        }
    
        public String getUsername() { 
            return username;
        }
    
        public void setUsername(String username) { 
            this.username = username;
        }
    
        public String getPassword() { 
            return password;
        }
    
        public void setPassword(String password) { 
            this.password = password;
        }
    
        @Override
        public String toString() { 
            return "User{" +
                    "id=" + id +
                    ", username='" + username + '\'' +
                    ", password='" + password + '\'' +
                    ", birthday=" + birthday +
                    '}';
        }
    }

1.  sqlConfigMapper 编写

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.feitian.dao.UserDao">
    
        
        <sql id="selectUser" >select  * from  user</sql>
        
        
        <select id="findByCondition" parameterType="user" resultType="user">
           <include refid="selectUser"/>
            <where>
                <if test="id != 0 ">
                    and id=#{id}
                </if>
                <if test="username != null">
                    and username=#{username}
                </if>
                <if test="password != null">
                    and password=#{password}
                </if>
            </where>
        </select>
        
        <select id="findByIds" resultType="user" parameterType="list">
            /*select * from user*/
            <include refid="selectUser"/>
            <where>
                <foreach collection="list" open="id in(" close=")" item="id" separator=",">
                    #{id}
                </foreach>
            </where>
        </select>
        
        
        <select id="findAll" resultType="user">
            select * from user
        </select>
        
        <delete id="delete" parameterType="java.lang.Integer">
            delete from user where id=#{abc}
        </delete>
        
        <update id="update" parameterType="com.feitian.pojo.User">
            update user set username=#{username},password=#{password} where id=#{id}
        </update>
        
        <insert id="save" parameterType="com.feitian.pojo.User">
            insert into user values(#{id},#{username},#{password})
        </insert>
    
        <insert id="saveUser" parameterType="user">
            insert into user values (#{id},#{username},#{password},#{birthday})
        </insert>
        
        <select id="findById" resultType="user" parameterType="java.lang.Integer">
            select * from user where id=#{id}
        </select>
    </mapper>

1.  UserMapper 编写

<?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>
    
        
        <typeAliases>
            <typeAlias type="com.feitian.pojo.User" alias="user"></typeAlias>
        </typeAliases>
    
        
        <typeHandlers>
            <typeHandler handler="com.feitian.handler.DateTypeHandler"></typeHandler>
        </typeHandlers>
    
        
        <plugins>
            <plugin interceptor="com.github.pagehelper.PageHelper"></plugin>
        </plugins>
        
        <environments default="developement">
            <environment id="developement">
                <transactionManager type="JDBC"></transactionManager>
                <dataSource type="POOLED">
                    <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>
            <mapper resource="com/feitian/mapper/UserMapper.xml"></mapper>
        </mappers>
    </configuration>

1.  jdbc 配置文件

jdbc.driver=com.mysql.jdbc.Driver
    jdbc.url=jdbc:mysql://localhost:3306/test
    jdbc.username=root
    jdbc.password=root

1.  log4j配置文件

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
    log4j.appender.stdout.Target=System.err
    log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
    log4j.appender.stdout.layout.ConversionPattern=%d{ ABSOLUTE} %5p %c{ 1}:%L - %m%n
    
    ### direct messages to file mylog.log ###
    log4j.appender.file=org.apache.log4j.FileAppender
    log4j.appender.file.File=c:/mylog.log
    log4j.appender.file.layout=org.apache.log4j.PatternLayout
    log4j.appender.file.layout.ConversionPattern=%d{ ABSOLUTE} %5p %c{ 1}:%L - %m%n
    
    ### set log levels - for more verbose logging change 'info' to 'debug' ###
    
    log4j.rootLogger=debug, stdout

1.  service 层代码编写

public class UserServiceImpl implements UserService { 
        @Test
        public void test01() throws IOException { 
            InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();
            UserDao userDao = sqlSession.getMapper(UserDao.class);
            PageHelper.startPage(2,2);
            List<User> userList = userDao.findAll();
            //获得与分页相关参数
            PageInfo<User> pageInfo = new PageInfo<User>(userList);
            System.out.println("当前页："+pageInfo.getPageNum());
            System.out.println("每页显示条数："+pageInfo.getPageSize());
            System.out.println("总条数："+pageInfo.getTotal());
            System.out.println("总页数："+pageInfo.getPages());
            System.out.println("上一页："+pageInfo.getPrePage());
            System.out.println("下一页："+pageInfo.getNextPage());
            System.out.println("是否是第一个："+pageInfo.isIsFirstPage());
            System.out.println("是否是最后一个："+pageInfo.isIsLastPage());
    
            sqlSession.close();
            for (User user:
                 userList) { 
                System.out.println("------------------");
                System.out.println(user);
            }
        }
    
        @Test
        public void test02() throws IOException { 
            InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();
            UserDao userDao = sqlSession.getMapper(UserDao.class);
            User user = new User();
            user.setId(1);
            user.setUsername("xxx");
            List<User> userList = userDao.findByCondition(user);
            System.out.println(userList);
        }
        @Test
        public void test03() throws IOException { 
            InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();
            UserDao userDao = sqlSession.getMapper(UserDao.class);
            List<Integer> ids = new ArrayList<Integer>() ;
            ids.add(0);
            ids.add(1);
            ids.add(2);
            List<User> userList = userDao.findByIds(ids);
            System.out.println(userList);
        }
    
        @Test
        public void test04() throws IOException { 
            InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();
            UserDao userDao = sqlSession.getMapper(UserDao.class);
            User user = new User();
            user.setId(1);
            user.setUsername("jack");
            user.setPassword("1234");
            user.setBirthday(new Date());
            userDao.saveUser(user);
            sqlSession.commit();
            sqlSession.close();
        }
    }

目录结构  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1ZXNoYW5mZWl0aWFu_size_16_color_FFFFFF_t_70 1]  
至此，本小结就复习到这里。

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