tomcat配置数据库连接池

由于基于HTTP协议的Web程序是无状态的，因此，在应用程序中使用JDBC时，每次处理客户端请求时都会重新建立数据库连接。如果客户端的请求频繁的话，这将会消耗很多的话资源。因此，tomcat提供了数据库连接池技术。数据库连接池负责分配、管理和释放数据库连接，它允许应用程序重复使用一个现有的数据库连接，而不是重新建立一个数据库连接。在使用一个数据库连接后，将其归还数据库连接池，以备其他程序使用。

1. 将JDBC mysql的驱动程序（mysql-connector-java-5.1.30-bin.jar）放入WEB-INF/lib文件夹。

2. 在META/inf文件夹新建context.xml文件。

写入

<Context path="/samples" docBase="samples" reloadable="true" crossContext="true"> 
<Resource 
name="jdbc/sitename" auth="Container" type="javax.sql.DataSource" 
maxActive="100" maxIdle="30" maxWait="10000" 
username="root" password="helloworld" driverClassName="com.mysql.jdbc.Driver" 
url="jdbc:mysql://localhost:3306/sitename?characterEncoding=GBK"/> 
</Context>

3.在WEB-INF/web.xml文件中写入

<resource-ref>
    <description>DB Connection</description>
    <res-ref-name>jdbc/sitename</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
</resource-ref>

4. 使用示例

package servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class ConnPool
 */
@WebServlet("/ConnPool")
public class ConnPool extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ConnPool() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setContentType("text/html");
        response.setCharacterEncoding("GBK");
        PrintWriter out =response.getWriter();
        try{
            javax.naming.Context ctx =new javax.naming.InitialContext();
            javax.sql.DataSource ds=(javax.sql.DataSource) ctx.lookup("java:comp/env/jdbc/sitename");
            Connection conn=ds.getConnection();
            PreparedStatement pstmt =((java.sql.Connection) conn).prepareStatement("SELECT user_id ,last_name FROM users");
            ResultSet rs=pstmt.executeQuery();
            StringBuilder table=new StringBuilder();
            table.append("<table border='1'>");
            table.append("<tr><td>用户编号</td><td>名字</td></tr>");
            while(rs.next()){
                table.append("<tr><td>"+rs.getString("user_id")+"</td><td>");
                table.append(rs.getString("last_name")+"</td></tr>");
            }
            table.append("</table>");
            out.println(table.toString());
        }catch(Exception e){
            out.println(e.getMessage());
        }
        out.flush();
        out.close();
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
    }

}