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局部数据源的使用

2024-07-13 20:53:48   223人阅读

1.我们都知道JDBC的固定步骤是以下几步组成：：

(1)Class.forName();

(2)Connection con  = DriverManager.getConnection();

(3)PreparedStatement stat = con.prepareStatement(sql);

(4)stat.executeQuery();

(5)con.close();

而(1)(2)(5)步是每次JDBC操作都要执行的，重复执行是非常耗时的，为了解决重复操作的问题，引入了数据源。

2.首先在WEB应用程序中的META-INF文件夹下，建立一个context.xml的文件。以下代码表示数据源名是jdbc/sampleDS.数据库的用户名是root.root用户对应的密码是123456.

<?xml version="1.0" encoding="UTF-8"?><Context reloadable="true"><Resource   name="jdbc/sampleDS"   type="javax.sql.DataSource"   maxActive="4"   maxIdle="2"   username="root"   maxWait="5000"   driverClassName="com.mysql.jdbc.Driver"   password="123456"   url="jdbc:mysql://127.0.0.1:3306/echarts" /></Context>

3.通过DataSource的名字查找对应的DataSource，通过一个DataSource在连接池中获得一个Connection

4.在servlet中使用

import java.io.IOException;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import javax.naming.Context;import javax.naming.InitialContext;import javax.naming.NamingException;import javax.servlet.RequestDispatcher;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.sql.DataSource;public class UserQueryServlet extends HttpServlet{    DataSource dataSource;        public void init(){        try{            //创建一个上下文对象            Context context = new InitialContext();            //然后通过它的lookup方法查找数据源对象            dataSource = (DataSource)context.lookup("java:comp/env/jdbc/sampleDS");        }catch(NamingException ne){            log("Exception:" + ne);        }    }    public void doPost(HttpServletRequest request,HttpServletResponse response)             throws ServletException,IOException{        Connection dbConnection=null;        try{            //获得数据库连接对象            dbConnection = dataSource.getConnection();        }catch(SQLException se){            log("Exctption:" + se);        }         response.setContentType("text/html;charset=UTF-8");         String UserName,password;            if( request.getParameter("username") !=null){            UserName = request.getParameter("username");            password = request.getParameter("password");            UserDAO userdao = new UserDAO();            UserBean userbean = userdao.searchUser(UserName);            request.getSession().setAttribute("user", userbean);                        try{                String sql = "SELECT*FROM user WHERE userName=?";                System.out.println(sql);                PreparedStatement pstmt = dbConnection.prepareStatement(sql);                pstmt.setString(1,UserName);                ResultSet rst = pstmt.executeQuery();                if(rst.next()) {                    UserBean user = new UserBean();                    user.setUserName(rst.getString("userName"));                    user.setPassword(rst.getString("userPassword"));                    request.getSession().setAttribute("username", UserName);                    if(user.getPassword().equals(password)){                        RequestDispatcher view = request.getRequestDispatcher("/showUser.jsp");                        view .forward(request, response);                    }else{                        RequestDispatcher view = request.getRequestDispatcher("/error.jsp");                        view .forward(request, response);                    }                                    }else{                    RequestDispatcher view = request.getRequestDispatcher("/error.jsp");                    view .forward(request, response);                }                                    }catch(SQLException e){                log("Exception: ",e);            }finally{                try{                    dbConnection.close();                }catch(SQLException e){}            }                }    }    public void doGet(HttpServletRequest request,HttpServletResponse response)             throws ServletException,IOException{        doPost(request,response);    }}

5.在JSP中使用

<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %><%@ page import="javax.naming.*,java.sql.*,javax.sql.*" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head>    <title>测试Tomcat局部数据源</title></head><body><%//初始化Context，使用InitialContext初始化ContextContext ctx=new InitialContext(); /*通过JNDI查找数据源，该JNDI为java:comp/env/jdbc/dstest，分成两个部分java:comp/env是Tomcat固定的，Tomcat提供的JNDI绑定都必须加该前缀jdbc/dstest是定义数据源时的数据源名*/DataSource ds=(DataSource)ctx.lookup("java:comp/env/jdbc/echarts");//获取数据库连接Connection conn=ds.getConnection();//获取StatementStatement stmt=conn.createStatement();//执行查询，返回ResulteSet对象ResultSet rs=stmt.executeQuery("select * from adminstore");while(rs.next()){    out.println(rs.getString(1)         + "\t" + rs.getString(2) + "<br/>");}%></body></html>


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