改善Servlet性能：从数据库中获取记录

在此示例中, 我们将提高Web应用程序从数据库中获取记录的性能。为此, 我们将表的数据存储在一个集合中, 然后在我们的servlet中重用该集合。因此, 我们不会直接一次又一次地访问数据库。这样, 我们正在改善性能。

要运行此应用程序, 你需要创建带有一些记录的下表。

CREATE TABLE  "CSUSER" 
   (	"USERID" NUMBER, "USERNAME" VARCHAR2(4000), "USERPASS" VARCHAR2(4000), "USEREMAIL" VARCHAR2(4000), "USERCOUNTRY" VARCHAR2(4000), "CONTACT" NUMBER, CONSTRAINT "CSUSER_PK" PRIMARY KEY ("USERID") ENABLE
   )
/

改善Servlet从数据库获取记录的性能的示例

在此示例中, 我们创建了6个页面。

1. index.html
2. User.java
3. MyListener.java
4. MyServlet1.java
5. MyServlet2.java
6. web.xml

1)index.html

该html文件包含两个将请求发送到servlet的链接。

<a href="servlet1">first servlet</a>|
<a href="servlet2">second servlet</a>

2) User.java

这是简单的bean类, 包含3个具有其getter和setter的属性。此类表示数据库表。

public class User {
private int id;
private String name, password;

public int getId() {
	return id;
}
public void setId(int id) {
	this.id = id;
}
public String getName() {
	return name;
}
public void setName(String name) {
	this.name = name;
}
public String getPassword() {
	return password;
}
public void setPassword(String password) {
	this.password = password;
}


}

3) MyListener.java

这是侦听器类。部署项目时, 默认情况下会调用ServletContextListener的contextInitialized方法。在这里, 我们获取表的记录并将其存储在添加到ArrayList类对象中的User类对象中。最后, 表的所有记录将存储在ArrayList类对象(集合)中。最后, 我们将ArrayList对象作为属性存储在ServletConext对象中, 以便我们可以在Servlet中获取它并使用它。

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.sql.*;
import java.util.ArrayList;

public class MyListener implements ServletContextListener{

 public void contextInitialized(ServletContextEvent e) {
		
  ArrayList list=new ArrayList();
   try{
    Class.forName("oracle.jdbc.driver.OracleDriver");
    Connection con=DriverManager.getConnection(
     "jdbc:oracle:thin:@localhost:1521:xe", "system", "oracle");
			
    PreparedStatement ps=con.prepareStatement("select * from csuser");
    ResultSet rs=ps.executeQuery();
    while(rs.next()){
     User u=new User();
     u.setId(rs.getInt(1));
     u.setName(rs.getString(2));
     u.setPassword(rs.getString(3));
     list.add(u);
    }
    con.close();
			
   }catch(Exception ex){System.out.print(ex);}

   //storing the ArrayList object in ServletContext		
   ServletContext context=e.getServletContext();
   context.setAttribute("data", list);
		
 }
 public void contextDestroyed(ServletContextEvent arg0) {
	System.out.println("project undeployed...");
 }

}

4) MyServlet1.java

该Servlet从Servlet上下文对象获取信息并进行打印。

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Iterator;
import java.util.List;

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


public class MyServlet1 extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse
   response)throws ServletException, IOException {

	response.setContentType("text/html");
	PrintWriter out = response.getWriter();
	
	long before=System.currentTimeMillis();
		
	ServletContext context=getServletContext();
	List list=(List)context.getAttribute("data");
		
	Iterator itr=list.iterator();
	while(itr.hasNext()){
	 User u=(User)itr.next();
	 out.print("<br>"+u.getId()+" "+u.getName()+" "+u.getPassword());
	}
		
	long after=System.currentTimeMillis();
	out.print("<br>total time :"+(after-before));
		
	out.close();
	}

}

5) MyServlet2.java

与MyServlet1相同。该Servlet从Servlet上下文对象获取信息并进行打印。

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.Iterator;
import java.util.List;

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


public class MyServlet2 extends HttpServlet {
 public void doGet(HttpServletRequest request, HttpServletResponse
   response)throws ServletException, IOException {

	response.setContentType("text/html");
	PrintWriter out = response.getWriter();
	
	long before=System.currentTimeMillis();
		
	ServletContext context=getServletContext();
	List list=(List)context.getAttribute("data");
		
	Iterator itr=list.iterator();
	while(itr.hasNext()){
	 User u=(User)itr.next();
	 out.print("<br>"+u.getId()+" "+u.getName()+" "+u.getPassword());
	}
		
	long after=System.currentTimeMillis();
	out.print("<br>total time :"+(after-before));
		
	out.close();
	}

}

6)web.xml

在这里, 我们包含有关servlet和侦听器的信息。

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 
 <listener>
 <listener-class>MyListener</listener-class>
 </listener>
 
 <servlet>
    <servlet-name>MyServlet1</servlet-name>
    <servlet-class>MyServlet1</servlet-class>
    
  </servlet>
  <servlet>
    <servlet-name>MyServlet2</servlet-name>
    <servlet-class>MyServlet2</servlet-class>
    
  </servlet>
  
   <servlet-mapping>
    <servlet-name>MyServlet1</servlet-name>
    <url-pattern>/servlet1</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>MyServlet2</servlet-name>
    <url-pattern>/servlet2</url-pattern>
  </servlet-mapping>
  
</web-app>

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