框架应用：Mybatis(二) - 动态SQL

MybatisUtil工具类

　　在实际开发中，我们可以编写一个MybatisUtil辅助类来进行对进行操作。

1）在静态初始化块中加载mybatis配置文件和StudentMapper.xml文件一次

2）使用ThreadLocal对象让当前线程与SqlSession对象绑定在一起

3）获取当前线程中的SqlSession对象，如果没有的话，从SqlSessionFactory对象中获取SqlSession对象

4）获取当前线程中的SqlSession对象，再将其关闭，释放其占用的资源

/**
 * MyBatis工具类
 * @author AdminTC
 */
public class MyBatisUtil {
    private static ThreadLocal<SqlSession> threadLocal = new ThreadLocal<SqlSession>();
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            Reader reader = Resources.getResourceAsReader("mybatis.xml");
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            e.printStackTrace();
            throw new RuntimeException(e);
        }
    }
    private MyBatisUtil(){}
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession == null){
            sqlSession = sqlSessionFactory.openSession();
            threadLocal.set(sqlSession);
        }
        return sqlSession;
    }
    public static void closeSqlSession(){
        SqlSession sqlSession = threadLocal.get();
        if(sqlSession != null){
            sqlSession.close();
            threadLocal.remove();
        }
    }
    public static void main(String[] args) {
        Connection conn = MyBatisUtil.getSqlSession().getConnection();
        System.out.println(conn!=null?"连接成功":"连接失败");
    }
}

MybatisUtil.java

　　

动态SQL

　　什么是动态SQL，如下图，当你不知道用户会选择多少个筛选条件的时候，你只有等待用户选择而动态地选择SQL查询条件。

　　

动态SQL-选择

　　加入IUserDao接口，注意因为与数据库互动需要，Dao接口一般要以类作为参数。

package com.harry.dao;
 
import java.sql.SQLException;
import java.util.List;
import java.util.Set;
 
import com.harry.entity.User;
 
public interface IUserDao {
     public boolean doCreate(User entity) throws Exception;
 
     public boolean doUpdate(User entity) throws Exception;
 
     public boolean doRemove(Set<Integer> ids)throws Exception;
 
     public User findById(Integer id)throws Exception;
 
     public List<User> findAll() throws  Exception;
 
     public List<User> findAllSplite(String column, String keyword, Integer currentPage, Integer lineSize) throws Exception;
 
     public Integer getAllCount(String column, String keyword) throws Exception;
}

IUserDao

　　书写UserDaoImpl,并在其后添加动态查询的查询方法dynaSQLwithSelect。

package com.harry.dao.impl;
 
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
 
import org.apache.ibatis.session.SqlSession;
 
import com.harry.dao.IUserDao;
import com.harry.entity.User;
import com.harry.util.MybatisUtil;
 
public class UserDaoImpl implements IUserDao {
 
    @Override
    public boolean doCreate(User entity) throws Exception {
        // TODO Auto-generated method stub
        return false;
    }
 
    @Override
    public boolean doUpdate(User entity) throws Exception {
        // TODO Auto-generated method stub
        return false;
    }
 
    @Override
    public boolean doRemove(Set<Integer> ids) throws Exception {
        // TODO Auto-generated method stub
        return false;
    }
 
    @Override
    public User findById(Integer id) throws Exception {
        // TODO Auto-generated method stub
        return null;
    }
 
    @Override
    public List<User> findAll() throws Exception {
        // TODO Auto-generated method stub
        return null;
    }
 
    @Override
    public List<User> findAllSplite(String column, String keyword, Integer currentPage, Integer lineSize)
            throws Exception {
        // TODO Auto-generated method stub
        return null;
    }
 
    @Override
    public Integer getAllCount(String column, String keyword) throws Exception {
        // TODO Auto-generated method stub
        return null;
    }
 
    public List<User> dynaSQLwithSelect(String uname,Character usex) throws Exception{
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        try{
            Map<String,Object> map = new LinkedHashMap<String, Object>();
            map.put("uname",uname);
            map.put("usex", usex);
            return sqlSession.selectList("dynaSQLwithSelect",map);
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            sqlSession.commit();
            MybatisUtil.closeSqlSession();
        }
    }
 
}

UserDaoImpl

　　在User.xml中配置相应的SQL方法映射。　　

<!-- map为调用该方法的外界传入 -->
    <select id="dynaSQLwithSelect" parameterType="map" resultType="com.harry.entity.User">
        select id,username,sex from user
        <where>
            <!-- 如果map中uname不为null，则在where后添加username = uname； -->
            <if test="uname!=null">
                and username=#{uname}
            </if>
            <!-- 如果map中usex不为null，则在where语句后添加 and sex = usex； -->
            <if test="usex!=null">
                and sex=#{usex}
            </if>
        </where>
    </select>

User.xml

　　测试方法

@Test
    public void testdynaSQLwithSelect() throws Exception {
        UserDaoImpl userDao = new UserDaoImpl();
        List<User> list = userDao.dynaSQLwithSelect("张飞", null);
        Iterator<User> iterator = list.iterator();
        while(iterator.hasNext()){
            System.out.println(iterator.next());
        }
    }

MybatisTest

　　动态SQL增删改查基本相同，重点是Mybatis通过在配置文件中书写<where>语句来避免数据库SQL拼接。

动态SQL-更新　

public boolean dynaSQLwithUpdate(Integer uid, String uname, String usex) throws Exception{
        //session应该在事务层进行开关，这里为了方便
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        try{
            Map<String,Object> map = new LinkedHashMap<>();
            map.put("uid", uid);
            map.put("uname", uname);
            map.put("usex", usex);
            sqlSession.update("dynaSQLwithUpdate",map);
            return true;
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            sqlSession.commit();
            MybatisUtil.closeSqlSession();
        }
    }

UserDaoImpl

<update id="dynaSQLwithUpdate" parameterType="map">
        UPDATE user
        <set>
            <if test="uname!=null">
                username=#{user.username},
            </if>
            <if test="usex!=null">
                sex=#{usex},
            </if>
        </set>
        where id=#{uid}
    </update>    

User.xml

动态SQL-删除

public boolean dynaSQLwithDelete(Integer... ids) throws Exception{
        //session应该在事务层进行开关，这里为了方便
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        try{
            Map<String, Object> map = new LinkedHashMap<>();
            map.put("ids", ids);
            sqlSession.delete("dynaSQLwithDelete",map);
            return true;
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            sqlSession.commit();
            MybatisUtil.closeSqlSession();
        }
    }

UserDaoImpl

<delete id="dynaSQLwithDelete" parameterType="map">
        DELETE FROM user WHERE id IN
        <!-- foreach 用来迭代数组元素 -->
        <!-- open表示开始符号 -->
        <!-- close表示结束符号 -->
        <!-- separator表示分隔符 -->
        <!-- item表示迭代的数组 -->
        <foreach collection="ids" open="(" close=")" separator="," item="id">
            #{id}
        </foreach>
    </delete>

User.xml

动态SQL- 插入

public boolean dynaSQLwithInsert(User... users) throws Exception{
        //session应该在事务层进行开关，这里为了方便
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        try{
            Map<String, Object> map = new LinkedHashMap<>();
            map.put("users", users);
            sqlSession.insert("dynaSQLwithInsert",map);
            return true;
        }catch(Exception e){
            e.printStackTrace();
            sqlSession.rollback();
            throw e;
        }finally{
            sqlSession.commit();
            MybatisUtil.closeSqlSession();
        }
    }

UserDaoImpl

<insert id="dynaSQLwithInsert" parameterType="map" useGeneratedKeys="true" keyProperty="id">
        INSERT INTO user (username, birthday, sex, address) VALUES
        <foreach collection="users" item="user" separator=",">
            (#{user.username},#{user.birthday},#{user.sex},#{user.address})
        </foreach>
    </insert>
</mapper>

User.xml

附Mybatis-2源码