mybatis的typeHandler

typeHandler作用：

　　1.传参时将javaType类型转换成jdbcType

　　2.结果集中ResultSet中取值时，jdbcType转换为javaType;

系统自定义的typeHandler:

　　mybatis系统内部定义了一系列的typeHandler；基本涵盖了我们正常使用的类型转换；如下

选取一个系统自定义的typeHandler看看；

在包org.apache.ibatis.type下有一个StringTypeHandler.java

源码如下：

public class StringTypeHandler extends BaseTypeHandler<String> {

  @Override
  public void setNonNullParameter(PreparedStatement ps, int i, String parameter, JdbcType jdbcType)
      throws SQLException {
    ps.setString(i, parameter);
  }

  @Override
  public String getNullableResult(ResultSet rs, String columnName)
      throws SQLException {
    return rs.getString(columnName);
  }

  @Override
  public String getNullableResult(ResultSet rs, int columnIndex)
      throws SQLException {
    return rs.getString(columnIndex);
  }

  @Override
  public String getNullableResult(CallableStatement cs, int columnIndex)
      throws SQLException {
    return cs.getString(columnIndex);
  }
}

StringTypeHandler继承了BaseTypeHandler;而BaseTypeHandler实现了接口TypeHandler,

BaseTypeHandler中代码

/**
 *    Copyright 2009-2015 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.type;

import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

import org.apache.ibatis.executor.result.ResultMapException;
import org.apache.ibatis.session.Configuration;

/**
 * @author Clinton Begin
 * @author Simone Tripodi
 */
public abstract class BaseTypeHandler<T> extends TypeReference<T> implements TypeHandler<T> {

  protected Configuration configuration;

  public void setConfiguration(Configuration c) {
    this.configuration = c;
  }

  @Override
  public void setParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException {
    if (parameter == null) {
      if (jdbcType == null) {
        throw new TypeException("JDBC requires that the JdbcType must be specified for all nullable parameters.");
      }
      try {
        ps.setNull(i, jdbcType.TYPE_CODE);
      } catch (SQLException e) {
        throw new TypeException("Error setting null for parameter #" + i + " with JdbcType " + jdbcType + " . " +
                "Try setting a different JdbcType for this parameter or a different jdbcTypeForNull configuration property. " +
                "Cause: " + e, e);
      }
    } else {
      try {
        setNonNullParameter(ps, i, parameter, jdbcType);
      } catch (Exception e) {
        throw new TypeException("Error setting non null for parameter #" + i + " with JdbcType " + jdbcType + " . " +
                "Try setting a different JdbcType for this parameter or a different configuration property. " +
                "Cause: " + e, e);
      }
    }
  }

  @Override
  public T getResult(ResultSet rs, String columnName) throws SQLException {
    T result;
    try {
      result = getNullableResult(rs, columnName);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column '" + columnName + "' from result set.  Cause: " + e, e);
    }
    if (rs.wasNull()) {
      return null;
    } else {
      return result;
    }
  }

  @Override
  public T getResult(ResultSet rs, int columnIndex) throws SQLException {
    T result;
    try {
      result = getNullableResult(rs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column #" + columnIndex+ " from result set.  Cause: " + e, e);
    }
    if (rs.wasNull()) {
      return null;
    } else {
      return result;
    }
  }

  @Override
  public T getResult(CallableStatement cs, int columnIndex) throws SQLException {
    T result;
    try {
      result = getNullableResult(cs, columnIndex);
    } catch (Exception e) {
      throw new ResultMapException("Error attempting to get column #" + columnIndex+ " from callable statement.  Cause: " + e, e);
    }
    if (cs.wasNull()) {
      return null;
    } else {
      return result;
    }
  }

  public abstract void setNonNullParameter(PreparedStatement ps, int i, T parameter, JdbcType jdbcType) throws SQLException;

  public abstract T getNullableResult(ResultSet rs, String columnName) throws SQLException;

  public abstract T getNullableResult(ResultSet rs, int columnIndex) throws SQLException;

  public abstract T getNullableResult(CallableStatement cs, int columnIndex) throws SQLException;

}

getResult分别用columnName和columnIndex从ResultSet中获取数据，CallableStatement表示从存储过程中获取结果及数据的方法；

下面我们创建自定义typeHandler

RoleMapper.java

package com.learn.charter2.mapper;

import java.util.List;

import com.learn.charter2.po.Role;

public interface RoleMapper {
    Role getRole(Long id) throws Exception;
    int deleteRole(Long id) throws Exception;
    int insertRole(Role role) throws Exception;
    List<Role> findRole(Role role) throws Exception;
}

Role.java

package com.learn.charter2.po;

public class Role {
    private Long id;
    private String roleName;
    private String note;
    private Integer pk;

    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getRoleName() {
        return roleName;
    }
    public void setRoleName(String roleName) {
        this.roleName = roleName;
    }
    public String getNote() {
        return note;
    }
    public void setNote(String note) {
        this.note = note;
    }
    public Integer getPk() {
        return pk;
    }
    public void setPk(Integer pk) {
        this.pk = pk;
    }

}

SqlSessionFactoryUtil.java

package com.learn.charter2.util;

import java.io.InputStream;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class SqlSessionFactoryUtil {
    private static SqlSessionFactory sqlSessionFactory=null;
    private static final Class class_lock=SqlSessionFactoryUtil.class;
    private SqlSessionFactoryUtil() {
    }
    public static SqlSessionFactory initSqlSessionFactory(){
        String resource="mybatis-config.xml";
        InputStream inputStream=null;
        try {
            inputStream=Resources.getResourceAsStream(resource);
        } catch (Exception e) {
            Logger.getLogger(SqlSessionFactoryUtil.class.getName()).log(Level.SEVERE,null,e);
        }
        synchronized (class_lock) {
            if(sqlSessionFactory==null){
                sqlSessionFactory=new SqlSessionFactoryBuilder().build(inputStream);
            }
        }
        return sqlSessionFactory;
    }
    public static SqlSession openSqlSession(){
        if(sqlSessionFactory==null){
            initSqlSessionFactory();
        }
        return sqlSessionFactory.openSession();
    }
}

log4j.properties

log4j.rootLogger=debug,stdout
log4j.logger.org.mybatis=debug
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p %d %C:%m%n

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>
     <typeHandlers>
         <typeHandler handler="com.learn.charter2.util.MyStringTypeHandler" javaType="string" jdbcType="VARCHAR"/>
         <typeHandler handler="com.learn.charter2.util.MyIntergerTypeHandler" javaType="int" jdbcType="VARCHAR"/>
     </typeHandlers>
     <environments default="development">
         <environment id="development">
             <transactionManager type="JDBC">
                 <property name="autoCommit" value="false" />
             </transactionManager>
             <dataSource type="POOLED">
                 <property name="driver" value="com.mysql.jdbc.Driver" />
                 <property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
                 <property name="username" value="root" />
                 <property name="password" value="gys" />
             </dataSource>
         </environment>
     </environments>
     <mappers>
         <mapper resource="com/learn/charter2/mapper/roleMapper.xml" />
     </mappers>
 </configuration>

roleMapper.xml

 <?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.learn.charter2.mapper.RoleMapper">

     <resultMap type="com.learn.charter2.po.Role" id="roleMap">
         <id column="id" property="id" javaType="long" jdbcType="BIGINT"/>
         <result column="role_name" property="roleName" javaType="string" jdbcType="VARCHAR"/>
         <result column="note" property="note" typeHandler="com.learn.charter2.util.MyStringTypeHandler"/>
         <result column="pk" property="pk" typeHandler="com.learn.charter2.util.MyIntergerTypeHandler"/>
     </resultMap>

     <select id="getRole" parameterType="long" resultMap="roleMap">
     select id,role_name as roleName,note from t_role where id=#{id}
     </select>

     <select id="findRole" parameterType="com.learn.charter2.po.Role" resultMap="roleMap">
     select id,role_name as roleName,note,pk from t_role
     <where>
         <if test="roleName !=null">
              role_name like concat('%',#{roleName,javaType=string,jdbcType=VARCHAR,typeHandler=com.learn.charter2.util.MyStringTypeHandler},'%')
         </if>
         <if test="pk !=null">
         and pk =#{pk,javaType=int,jdbcType=VARCHAR,typeHandler=com.learn.charter2.util.MyIntergerTypeHandler}
          </if>
     </where>    

     </select>

     <insert id="insertRole" parameterType="com.learn.charter2.po.Role">
         insert into t_role
         (role_name,note)
         values
         (#{roleName},#{note})
     </insert>
     <delete id="deleteRole" parameterType="long">
         delete from t_role where id=#{id}
     </delete>
 </mapper>

MyIntergerTypeHandler.java

 package com.learn.charter2.util;

 import java.sql.CallableStatement;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;

 import org.apache.ibatis.type.JdbcType;
 import org.apache.ibatis.type.MappedJdbcTypes;
 import org.apache.ibatis.type.MappedTypes;
 import org.apache.ibatis.type.TypeHandler;
 import org.apache.log4j.Logger;

 import sun.security.action.GetIntegerAction;

 /**
  * @MappedTypes({Integer.class})
    @MappedJdbcTypes(JdbcType.VARCHAR)
  *
  */
 public class MyIntergerTypeHandler implements TypeHandler<Integer> {

     private Logger log=Logger.getLogger(MyIntergerTypeHandler.class);

     private int getInt(String v){
         if("a".equals(v)){
             return 10;
         }else if("b".equals(v)){
             return 20;
         }else if("c".equals(v)){
              return 30;
         }else{
             return 60;
         }
     }
     @Override
     public Integer getResult(CallableStatement cs, int index)
             throws SQLException {
         log.info("使用我的IntegerTypeHandler,CallbleStatment下表获取字符串");
         return getInt(cs.getString(index));
     }

     @Override
     public Integer getResult(ResultSet rs, int index) throws SQLException {
         log.info("使用我的IntegerTypeHandler,ResultSet下标获取字符串");
         return getInt(rs.getString(index));
     }

     @Override
     public Integer getResult(ResultSet rs, String colName) throws SQLException {
         log.info("使用我的IntegerTypeHandler,ResultSet 列名获取字符串");
         return getInt(rs.getString(colName));
     }

     @Override
     public void setParameter(PreparedStatement ps, int index, Integer value,JdbcType jt) throws SQLException {
         log.info("使用我的IntegerTypeHandler==index:"+index+";value:"+value);
         String v="";
         if(value==1){
             v="a";
         }else if(value==2){
             v="b";
         }else if(value==3){
             v="c";
         }else {
             v="guoyansi";
         }
         ps.setString(index, v);
     }
 }

MyStringTypeHandler.java

 package com.learn.charter2.util;

 import java.sql.CallableStatement;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.SQLException;

 import org.apache.ibatis.type.JdbcType;
 import org.apache.ibatis.type.MappedJdbcTypes;
 import org.apache.ibatis.type.MappedTypes;
 import org.apache.ibatis.type.TypeHandler;
 import org.apache.log4j.Logger;

 @MappedTypes({String.class})
 @MappedJdbcTypes(JdbcType.INTEGER)
 public class MyStringTypeHandler implements TypeHandler<String> {
     private Logger log=Logger.getLogger(MyStringTypeHandler.class);

     @Override
     public String getResult(CallableStatement cs, int index)
             throws SQLException {
         log.info("使用我的StringTypeHandler,CallbleStatment下表获取字符串");
         return cs.getString(index);
     }

     @Override
     public String getResult(ResultSet rs, int index) throws SQLException {
         log.info("使用我的StringTypeHandler,ResultSet下标获取字符串");
         return rs.getString(index);
     }

     @Override
     public String getResult(ResultSet rs, String colName) throws SQLException {
         log.info("使用我的StringTypeHandler,ResultSet 列名获取字符串");
         return rs.getString(colName);
     }

     @Override
     public void setParameter(PreparedStatement ps, int index, String value,
             JdbcType jt) throws SQLException {
         value=value+"m";
         log.info("使用我的StringTypeHandler==index:"+index+";value:"+value);
         ps.setString(index, value);
     }

 }

Charter2Main.java

 package com.learn.charter2.main;

 import java.util.List;

 import org.apache.ibatis.session.SqlSession;

 import com.learn.charter2.mapper.RoleMapper;
 import com.learn.charter2.po.Role;
 import com.learn.charter2.util.SqlSessionFactoryUtil;

 public class Charter2Main {
     public static void main(String[] args) {
         SqlSession sqlSession = null;
         try {
             sqlSession = SqlSessionFactoryUtil.openSqlSession();
             RoleMapper roleMapper = sqlSession.getMapper(RoleMapper.class);
             Role role = new Role();
             role.setPk(10);
             List<Role> list=roleMapper.findRole(role);
             for(Role r:list){
                 System.out.println("id:"+r.getId()+";roleName:"+r.getRoleName()+";note:"+r.getNote()+";pk:"+r.getPk());
             }
         } catch (Exception e) {
             System.err.println(e.getMessage());
             sqlSession.rollback();
         }finally{
             if(sqlSession!=null){
                 sqlSession.close();
             }
         }
     }

 }

自定义typeHandler的三个步骤：

1.定义typeHandler(MyIntergerTypeHandler.java     MyStringTypeHandler.java)

2.配置typeHandler(mybatis-config.xml中3-6行)

3.指定入参中哪个字段使用typeHandler(mapper.xml中19-24行)

4.指定出参中哪个字段使用typeHandler(mapper.xml中7-8行)

以MyIntergerTypeHandler为例，运行一下Charter2Main.java

Charter2Main 中传入的pk参数是10，被typeHandler默默的转换成了guoyansi;
因为guoyansi在数据库中找到了值，在被返回到java中，guoyansi又被typeHandler转化成了60；
这个例子展示的就是Integer和String之间的转换。