配置servlet连接池

具体操作过程：

1、配置全局数据库连接池

在<tomcat安装目录>\conf\server.xml文件中找到<GlobalNamingResources>标签，添加下列配置：

 <Resource name="jdbc/webdb"
           auth="Container"
               type="javax.sql.DataSource"
               driverClassName="com.mysql.jdbc.Driver"
               url="jdbc:mysql://localhost:3306/webdb?characterEncoding=UTF-8"
               username="root"
           password="root"
           maxActive="200"
           maxIdle="50"
           maxWait="3000" />

2、下载JDBC驱动的jar包，放在tomcat的lib目录下
3、在创建的webdemo工程中web.xml文件中增加下列配置：

 <resource-ref>
     <res-ref-name>jdbc/webdb</res-ref-name>
     <res-type>javax.sql.DataSource</res-type>
     <res-auth>Container</res-auth>
     <res-sharing-scope>Shareable</res-sharing-scope>
  </resource-ref>

4、在webdemo工程的META-INF目录下增加一个context.xml文件，内容如下：

 <?xml version="1.0" encoding="UTF-8"?>
 <Context>
   <Listener className="org.apache.catalina.startup.TldConfig"/>
   <Listener className="org.apache.catalina.startup.TldConfig"/>
   <Listener className="org.apache.catalina.startup.TldConfig"/>
   <Listener className="org.apache.catalina.startup.TldConfig"/>
   <Resource
    auth="Container"
     description="webdb"
     name="jdbc/webdb"
     password="root"
     username="root"
     type="javax.sql.DataSource"
     driverClassName="com.mysql.jdbc.Driver"
     url="jdbc:mysql://localhost:3306/webdb?characterEncoding=UTF-8" />
 </Context>

5、访问数据库事例java文件

 package chapter4;

 import java.io.IOException;
 import java.io.PrintWriter;

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

 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;

 public class Helloworld extends HttpServlet {

     public void doGet(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {

         response.setContentType("text/html; charset=UTF-8");
         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/webdb");


             Connection conn = ds.getConnection();
             PreparedStatement pst = conn.prepareStatement("SELECT * FROM t_dictionary");
             ResultSet rs = pst.executeQuery();
             StringBuilder table = new StringBuilder();
             table.append("<table border='1'>");
             table.append("<tr><td>eg-name</td><td>ch-name</td></tr>");
             while(rs.next())
             {
                 table.append("<tr><td>"+rs.getString("english")+"</td><td>");
                 table.append(rs.getString("chinese")+"</td></tr>");
             }
             table.append("</table>");
             out.println(table.toString());
             pst.close();
         }
         catch(Exception e)
         {
             out.println(e.getMessage());
         }
     }

 }