mybatis 基础01

 hibernate 比较不好的一点 就是全表映射，

比如不好定制 sql, 把表中的所有字段都 select 出来，增加网络开销 和 序列化的开销，增加了 CPU 的操作

使用 hibernate 不需要 写 sql,屏蔽了 sql, 不利于 调优

项目日志导入：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.enjoylearing.mybatis</groupId>
    <artifactId>mybatis-quick-start</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <dependencies>
        <!-- 单元测试相关依赖 -->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>4.3.2.RELEASE</version>
            <scope>test</scope>
        </dependency>

        

        <!-- 日志相关依赖 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.10</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.1.2</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
            <version>1.1.2</version>
        </dependency>

        <!-- mysql驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.18</version>
        </dependency>


        <!-- mybatis相关依赖 -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.1</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.1</version>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.3.2</version>
                <configuration>
                    <verbose>true</verbose>
                    <overwrite>true</overwrite>
                </configuration>
            </plugin>


        </plugins>
    </build>

</project>

package com.enjoylearning.mybatis;
//STEP 1. 导入sql相关的包
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import org.junit.Test;

import com.enjoylearning.mybatis.entity.TUser;

public class JdbcDemo {
    static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
    static final String DB_URL = "jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf8&allowMultiQueries=true";

    // Database credentials
    static final String USER = "root";
    static final String PASS = "422525";

    @Test
    public void QueryStatementDemo() {
        Connection conn = null;
        Statement stmt = null;
        List<TUser> users = new ArrayList<>();
        try {
            // STEP 2: 注册mysql的驱动
            Class.forName("com.mysql.jdbc.Driver");

            // STEP 3: 获得一个连接
            System.out.println("Connecting to database...");
            conn = DriverManager.getConnection(DB_URL, USER, PASS);

            // STEP 4: 创建一个查询
            System.out.println("Creating statement...");
            stmt = conn.createStatement();
            String userName = "lison";
            String sql="SELECT * FROM t_user where user_name='"+userName+"'";
            ResultSet rs = stmt.executeQuery(sql);
            System.out.println(stmt.toString());
            

            // STEP 5: 从resultSet中获取数据并转化成bean
            while (rs.next()) {
                System.out.println("------------------------------");
                // Retrieve by column name
                TUser user = new TUser();
//                user.setId(rs.getInt("id"));
//                user.setUserName(rs.getString("user_name"));
                user.setRealName(rs.getString("real_name"));
                user.setSex(rs.getByte("sex"));
                user.setMobile(rs.getString("mobile"));
                user.setEmail(rs.getString("email"));
                user.setNote(rs.getString("note"));

                System.out.println(user.toString());
                
                users.add(user);
            }
            // STEP 6: 关闭连接
            rs.close();
            stmt.close();
            conn.close();
        } catch (SQLException se) {
            // Handle errors for JDBC
            se.printStackTrace();
        } catch (Exception e) {
            // Handle errors for Class.forName
            e.printStackTrace();
        } finally {
            // finally block used to close resources
            try {
                if (stmt != null)
                    stmt.close();
            } catch (SQLException se2) {
            }// nothing we can do
            try {
                if (conn != null)
                    conn.close();
            } catch (SQLException se) {
                se.printStackTrace();
            }
        }
        System.out.println("-------------------------");
        System.out.println("there are "+users.size()+" users in the list!");
    }
    
    
    @Test
    public void QueryPreparedStatementDemo() {
        Connection conn = null;
        PreparedStatement stmt = null;
        List<TUser> users = new ArrayList<>();
        try {
            // STEP 2: 注册mysql的驱动
            Class.forName("com.mysql.jdbc.Driver");

            // STEP 3: 获得一个连接
            System.out.println("Connecting to database...");
            conn = DriverManager.getConnection(DB_URL, USER, PASS);

            // STEP 4: 创建一个查询
            System.out.println("Creating statement...");
            String sql;
            sql = "SELECT * FROM t_user where user_name= ? ";
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, "lison");
            System.out.println(stmt.toString());//打印sql
            ResultSet rs = stmt.executeQuery();
            

            // STEP 5: 从resultSet中获取数据并转化成bean
            while (rs.next()) {
                System.out.println("------------------------------");
                // Retrieve by column name
                TUser user = new TUser();
//                user.setId(rs.getInt("id"));
//                user.setUserName(rs.getString("user_name"));
                user.setRealName(rs.getString("real_name"));
                user.setSex(rs.getByte("sex"));
                user.setMobile(rs.getString("mobile"));
                user.setEmail(rs.getString("email"));
                user.setNote(rs.getString("note"));

                System.out.println(user.toString());
                
                users.add(user);
            }
            // STEP 6: 关闭连接
            rs.close();
            stmt.close();
            conn.close();
        } catch (SQLException se) {
            // Handle errors for JDBC
            se.printStackTrace();
        } catch (Exception e) {
            // Handle errors for Class.forName
            e.printStackTrace();
        } finally {
            // finally block used to close resources
            try {
                if (stmt != null)
                    stmt.close();
            } catch (SQLException se2) {
            }// nothing we can do
            try {
                if (conn != null)
                    conn.close();
            } catch (SQLException se) {
                se.printStackTrace();
            }
        }
        System.out.println("-------------------------");
        System.out.println("there are "+users.size()+" users in the list!");
    }

    @Test
    public void updateDemo(){
        Connection conn = null;
        PreparedStatement stmt = null;
        try {
            // STEP 2: 注册mysql的驱动
            Class.forName("com.mysql.jdbc.Driver");

            // STEP 3: 获得一个连接
            System.out.println("Connecting to database...");
            conn = DriverManager.getConnection(DB_URL, USER, PASS);
            
            // STEP 4: 启动手动提交
            conn.setAutoCommit(false);
            

            // STEP 5: 创建一个更新
            System.out.println("Creating statement...");
            String sql = "update t_user  set mobile= ? where user_name= ? ";
            stmt = conn.prepareStatement(sql);
            stmt.setString(1, "186995587411");
            stmt.setString(2, "lison");
            System.out.println(stmt.toString());//打印sql
            int ret = stmt.executeUpdate();
            System.out.println("此次修改影响数据库的行数为："+ret);

            // STEP 6: 手动提交数据
            conn.commit();
            
            // STEP 7: 关闭连接
            stmt.close();
            conn.close();
        } catch (SQLException se) {
            // Handle errors for JDBC
            try {
                conn.rollback();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            se.printStackTrace();
        } catch (Exception e) {
            try {
                conn.rollback();
            } catch (SQLException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            e.printStackTrace();
        } finally {
            // finally block used to close resources
            try {
                if (stmt != null)
                    stmt.close();
            } catch (SQLException se2) {
            }// nothing we can do
            try {
                if (conn != null)
                    conn.close();
            } catch (SQLException se) {
                se.printStackTrace();
            }
        }
    }
}

 使用 maven 快速应用：

package com.enjoylearning.mybatis;

import java.io.IOException;
import java.io.InputStream;

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

import com.enjoylearning.mybatis.entity.TUser;
import com.enjoylearning.mybatis.mapper.TUserMapper;

public class MybatisQuickStart {

    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void init() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        // 1.读取mybatis配置文件创SqlSessionFactory
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        inputStream.close();
    }

    @Test
    // 快速入门
    public void quickStart() throws IOException {
        // 2.获取sqlSession
        SqlSession sqlSession = sqlSessionFactory.openSession();
        // 3.获取对应mapper
        TUserMapper mapper = sqlSession.getMapper(TUserMapper.class);
        // 4.执行查询语句并返回结果
        TUser user = mapper.selectByPrimaryKey(1);
        System.out.println(user.toString());

    }
    
}

mybatis 的配置 ： 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="db.properties" />

    <settings>
        <setting name="mapUnderscoreToCamelCase" value="true" />
    </settings>


    <!--配置environment环境 -->
    <environments default="development">
        <!-- 环境配置1，每个SqlSessionFactory对应一个环境 -->
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="UNPOOLED">
                <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>

    <!-- 映射文件，mapper的配置文件 -->
<!--     <mappers>
        直接映射到相应的mapper文件
        <mapper resource="sqlmapper/TUserMapper.xml" />
    </mappers> -->

    <mappers>
        <mapper class="com.enjoylearning.mybatis.mapper.TUserMapper" />
    </mappers>


</configuration>  

mybatis 常用属性总结：

 配置 typeAliases 别名， mapper.xml 就不需要写全路径了

typeHandler  自定义类型转换：

mybatis 有一个注册中心的概念， 可以将 java的 类型 映射成 数据库的类型

 可以点进去 看一个 BigDecimalTypeHandler 

/**
 *    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.math.BigDecimal;
import java.sql.CallableStatement;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

/**
 * @author Clinton Begin
 */
public class BigDecimalTypeHandler extends BaseTypeHandler<BigDecimal> {

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

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

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

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

我们可以自定义 一个 TypeHandler , 继承 mybatis 实现的 接口，就可以自动进行类型转化了。