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。
- index.html
- User.java
- MyListener.java
- MyServlet1.java
- MyServlet2.java
- 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>下载此示例(使用Myeclipse IDE开发)
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