Mybatis 第一个Demo

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项目结构  以及表结构:

第一步.导入相应的Mybatis包放在web-app的lib文件夹下并加入路径

第二步.创建实体类Message

package Com.Entity;public class Message {//主键   private int id;   //指令   private String command;   //描述   private String description;   //内容   private String content;      public Message(){      }public int getId() {return id;}public void setId(int id) {this.id = id;}public String getCommand() {return command;}public void setCommand(String command) {this.command = command;}public String getDescription() {return description;}public void setDescription(String description) {this.description = description;}public String getContent() {return content;}public void setContent(String content) {this.content = content;}   }

第三步.创建核心配置文件（把数据库的信息配置进核心文件）Configuration.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><!--   <settings>    <setting name="useGeneratedKeys" value="false"/>    <setting name="useColumnLabel" value="true"/>  </settings>  <typeAliases>    <typeAlias alias="UserAlias" type="org.apache.ibatis.submitted.complex_property.User"/>  </typeAliases> -->  <environments default="development">    <environment id="development">      <transactionManager type="JDBC">        <property name="" value=""/>      </transactionManager>      <dataSource type="UNPOOLED">        <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="123456"/>      </dataSource>    </environment>  </environments><!-- 配置Message.xml文件 -->  <mappers>    <mapper resource="Com/config/sqlxml/Message.xml"/>  </mappers> </configuration>

第四步.实现db层（和数据库交互的类）

package Com.DB;import java.io.IOException;import java.io.Reader;import org.apache.ibatis.io.Resources;import org.apache.ibatis.session.SqlSession;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;/** * 正真和数据库交互：db层 * 编写访问数据库类 * @author liu * */public class DBAccess {//把异常向上抛，抛给DAO层  因为Dao层捕获异常，拿到SqlSession在finally中关闭SqlSession这个对象   public  SqlSession getSqlSession() throws IOException{   //1.通过配置文件获取配置信息 是一个路径就不能写点了   从src下开始 Reader reader=Resources.getResourceAsReader("Com/config/Configuration.xml"); //2.通过配置信息创建一个sqlSesisonFactory  SqlSessionFactory sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);  //3.通过sqlSesisonFactory打开一个sqlSession  SqlSession sqlSession=sqlSessionFactory.openSession();return sqlSession;   }}

第五步.配置Message.xml文件（相当于JDBC中的写sql语句和查询结果的赋值给Message对象）

<?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"><!-- 配置好了字段和属性，sql语句等  要把这个配置文件注册到核心配置文件Configuration.xml中 --><mapper namespace="Message">  <resultMap type="Com.Entity.Message" id="MessageResult">  <!--       id：是主键名   result:是普通字段的名字  column指的是数据库里面的字段  property指的是实体类中的属性    数据库里面的字段类型与jdbcType里面的字段类型有一种对应关系    jdbc      jdbcType    int       INTEGER    varchar   VARCHAR  -->    <id column="ID" jdbcType="INTEGER" property="id"/>    <result column="COMMAND" jdbcType="VARCHAR" property="command"/>    <result column="DESCRIPTION" jdbcType="VARCHAR" property="description"/>    <result column="CONTENT" jdbcType="VARCHAR" property="content"/>  </resultMap><!-- id为这个sql语句起一个唯一的名字（是在所有的配置文件中不能重名  ，以后不只一个配置文件）                       记住是唯一的 以后的sql语句不能重名  但是在不同的<mapper namespace="">中                     相同的ID是可以存在的                     sql语句的resultMap属性是指向resultMap标签的  所以resultMap标签的id就是sql语句resultMap属性的值                     -->  <select id="selectbycommand"  resultMap="MessageResult">    SELECT ID,COMMAND,DESCRIPTION,CONTENT FROM message where 1=1  </select> </mapper>

第六步..编写Dao层

package Com.DAO;import java.io.IOException;import java.sql.Connection;import java.sql.DriverManager;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;import org.apache.ibatis.session.SqlSession;import Com.DB.DBAccess;import Com.Entity.Message;       /*        * 和Message表相关的处理类        */public class Service {//返回的是符合条件的Message集合--》 Mybatis版public List<Message> selectbycommand(String command,String description){DBAccess dbAccess=new DBAccess();List<Message>  messagelist=new ArrayList<Message>();//sqlSession放在外面 无论如何都可以关掉SqlSession sqlSession=null; //处理DB层抛上来的异常try{sqlSession=dbAccess.getSqlSession();//调用Message.xml文件中得sql语句获取返回结果并把每个message对象添加到messagelist中messagelist=sqlSession.selectList("Message.selectbycommand");}catch(IOException ex){ex.printStackTrace();}finally{if(sqlSession!=null){sqlSession.close();}}return messagelist;}//返回的是符合条件的Message集合--》 JDBC版/*public List<Message> selectbycommand(String command,String description){    List<Message>  messagelist=new ArrayList<Message>(); try {Class.forName("com.mysql.jdbc.Driver");Connection conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=UTF8","root","123456");List<String> paramlist =new ArrayList<String>();StringBuffer sql=new StringBuffer("SELECT ID,COMMAND,DESCRIPTION,CONTENT FROM message where 1=1");if(command!=null&&!"".equals(command.trim())){//前面有空格或者sql字符串末尾加空格不然会报错sql.append(" and COMMAND=? ");paramlist.add(command);}if(description!=null&&!"".equals(description.trim())){sql.append(" and DESCRIPTION like '%' ? '%'");paramlist.add(description);}    PreparedStatement ptmt=conn.prepareStatement(sql.toString());    for(int i=0;i<paramlist.size();i++){     ptmt.setString(i+1, paramlist.get(i));          System.out.println("加入的字符串:"+paramlist.get(i));    }           Message mess=null;   ResultSet rs= ptmt.executeQuery();   while(rs.next()){   mess=new Message();   mess.setId(rs.getInt("ID"));   mess.setCommand(rs.getString("COMMAND"));   mess.setDescription(rs.getString("DESCRIPTION"));   mess.setContent(rs.getString("CONTENT"));   messagelist.add(mess);   }  } catch (ClassNotFoundException e) {// TODO Auto-generated catch blocke.printStackTrace();} catch (SQLException e) {// TODO Auto-generated catch blocke.printStackTrace();} return messagelist; }*/}            

第七步.编写Servlet并配置进web.xml文件

package Com.Servlet;import java.io.IOException;import java.io.PrintWriter;import java.util.List;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import Com.DAO.Service;import Com.Entity.Message;public class ListServlet extends HttpServlet {/**列表页面初始化控制 * The doGet method of the servlet. <br> */ public List<Message>  messagelist=null;public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {        request.setCharacterEncoding("utf-8");response.setContentType("text/html;charset=utf-8");//接收页面的值String command=request.getParameter("command");String description =request.getParameter("description");System.out.println("获取的参数："+request.getParameter("command"));//向页面传值request.setAttribute("command",command);request.setAttribute("description",description);//查询消息列表并传递给页面Service service=new Service();messagelist=service.selectbycommand(command,description);//放入request中     request.setAttribute("messagelist", messagelist);   System.out.println("加入成功");//服务器内部转发request内保存的值就不会过期      //跳转页面     request.getRequestDispatcher("/list.jsp").forward(request, response);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp)throws ServletException, IOException {// TODO Auto-generated method stubthis.doGet(req, resp);}   }

<servlet-mapping>    <servlet-name>ListServlet</servlet-name>    <url-pattern>/List.action</url-pattern>  </servlet-mapping>  <welcome-file-list>    <welcome-file>index.jsp</welcome-file>  </welcome-file-list></web-app>

list.jsp文件

<%@ page language="java" import="java.util.*"contentType="text/html; charset=utf-8"%><%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%><%String path = request.getContextPath();String basePath = request.getScheme() + "://"+ request.getServerName() + ":" + request.getServerPort()+ path + "/";%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><meta http-equiv="X-UA-Compatible" content="IE=9; IE=8; IE=7; IE=EDGE" /><title>内容列表页面</title><link href="<%=basePath%>resource/css/all.css" rel="stylesheet"type="text/css" /></head><body style="background: #e1e9eb;"><form action="<%=basePath%>List.action" id="mainForm" method="post"><div class="right"><div class="current">当前位置：<a href="javascript:void(0)" style="color:#6E6E6E;">内容管理</a>> 内容列表</div><div class="rightCont"><p class="g_title fix">内容列表 <a class="btn03" href="#">新 增</a>    <aclass="btn03" href="#">删 除</a></p><table class="tab1"><tbody><tr><td width="90" align="right">指令名称：</td><td><input name="command" type="text" class="allInput" value="${command}" /></td><td width="90" align="right">描述：</td><td><input name="description" type="text" class="allInput" value="${description}" /></td><td width="85" align="right"><input type="submit"class="tabSub" value="查 询" /></td></tr></tbody></table><div class="zixun fix"><table class="tab2" width="100%"><tbody><tr><th><input type="checkbox" id="all" onclick="" /></th><th>序号</th><th>指令名称</th><th>描述</th><th>操作</th></tr><c:forEach items="${messagelist}" var="message"varStatus="status"><tr<c:if test="${status.index%2!=0 }">style="background-color:#ECF6EE;"</c:if>><td><input type="checkbox" /></td><td>${status.index+1 }</td><td>${message.command }</td><td>${message.description }</td><td><a href="#">修改</a>    <a href="#">删除</a></td></tr></c:forEach></tbody></table><div class='page fix'>共 <b>4</b> 条 <a href='###' class='first'>首页</a> <a href='###'class='pre'>上一页</a> 当前第<span>1/1</span>页 <a href='###'class='next'>下一页</a> <a href='###' class='last'>末页</a> 跳至 <inputtype='text' value='1' class='allInput w28' /> 页  <ahref='###' class='go'>GO</a></div></div></div></div></form></body></html>

小结：

Model层：实体类

DB层（数据库层）：加载驱动，获取链接
Dao层：执行SQL语句，获取操作结果封装消息，返回操作结果其中的操作就会用到Model层

Servlet：一般就是--》接收页面的值，向页面传值，查询消息列表（Dao层的操作结果）并返回给页面，向页面跳转

View层：接收Servlet的资源呈现给用户

各层之间如何耦合：如--》在Servlet层创建Dao层具体操作类的对象