Servlet学习（个人笔记）
问：简述Servlet的生命周期？
在Servlet产生到消亡的过程中，有三个生命周期函数，初始化方法init(),处理客户请求的方法service(),终止方法destroy()。
另外，具体是以下过程
（1）加载和实例化
当Servlet容器启动或客户端发送一个请求时，Servlet容器会查找内存中是否存在该Servlet实例，若存在，则直接读取该实例响应请求；如果不存在，就创建一个Servlet实例。
（2） 初始化
实例化后，Servlet容器将调用Servlet的init()方法进行初始化（一些准备工作或资源预加载工作）。
（3）服务
初始化后，Servlet处于能响应请求的就绪状态。当接收到客户端请求时，调用service()的方法处理客户端请求，HttpServlet的service()方法会根据不同的请求 转调不同的doXxx()方法。
（4）销毁
当Servlet容器关闭时，Servlet实例也随时销毁。其间，Servlet容器会调用Servlet 的destroy()方法去判断该Servlet是否应当被释放（或回收资源）。
servlet文件下载
package com.mine;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
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 Test
* 实现文件下载
*/
@WebServlet("/Test")
public class Test extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* Default constructor.
*/
public Test() {
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//得到文件路径
String path = this.getServletContext().getRealPath("/pictures/中文文件.jpeg");
//得到文件名（最后一个\之后的都是文件名）
String filename = path.substring( path.lastIndexOf("\\")+1 );
//英文文件名用这个
//response.setHeader("content-disposition", "attachment;filename="+filename);
//如果下载文件是中文文件名，则麻烦一点，需要url编码
response.setHeader("content-disposition", "attachment;filename="+URLEncoder.encode(filename, "UTF-8") );
InputStream in = null;
OutputStream out = null;
in = new FileInputStream(path);
int len = 0;
byte buffer[] = new byte[1024];
out = response.getOutputStream();
while( (len = in.read(buffer) ) > 0 )
{
out.write(buffer,0,len);
}
in.close();
out.close();
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
3s刷新页面，并随机输出一个数
package com.mine;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
import java.util.Random;
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 Test
* 每隔3s刷新页面，随机输出一个数
*/
@WebServlet("/Test")
public class Test extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* Default constructor.
*/
public Test() {
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setHeader("refresh", "3");
String data = new Random().nextInt(100)+"";
response.getOutputStream().write(data.getBytes());
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
实现跳转
package com.mine;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
import java.util.Random;
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 Test
* 实现页面跳转
*/
@WebServlet("/Test")
public class Test extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* Default constructor.
*/
public Test() {
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//response.getOutputStream().write("你好".getBytes());
deal(request, response);
}
private void deal(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//这里的编码问题没有解决，还是乱码，不知道为啥
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
//包含html语句的message
String message ="clickhere跳转";
this.getServletContext().setAttribute("message", message);
this.getServletContext().getRequestDispatcher("/WEB-INF/message.jsp").forward(request, response);
}
//其实还可以用request实现转发，代码如下
private void test5(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String data = "yyeee";
request.setAttribute("data", data);
request.getRequestDispatcher("/message.jsp").forward(request, response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
request学习代码
package com.mine;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.Map;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.beanutils.BeanUtils;
/**
*
*/
@WebServlet("/Test2")
public class Test2 extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public Test2() {
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.getWriter().append("Served at: ").append(request.getContextPath());
test3(request,response);
}
//通过HTML页面传递数据，HTML页面是test.html
private void test3(HttpServletRequest request, HttpServletResponse response) {
Enumeration names = request.getParameterNames();
while( names.hasMoreElements() )
{
String s = names.nextElement();
String value = request.getParameter(s);
System.out.println(s+" = "+value);
}
System.out.println("-------获取数据的另一种方式---------------");
Map map = request.getParameterMap();
User user = new User();
try {
//从map中取出符合user属性的值，也就是，用户输入的用户名和密码可以很方便的存在ueser对象中
BeanUtils.populate(user, map);
} catch ( Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("name: "+user.getUsername()+" pass: "+user.getPassword() );
}
//获取头的相关方法
private void test2(HttpServletRequest request, HttpServletResponse response) {
//获取单个头
String headValue = request.getHeader("Accept-Encoding");
System.out.println(headValue);
//获取所有叫这个名字的头
Enumeration e = request.getHeaders("Accept-Encoding");
while( e.hasMoreElements() )
{
String s = e.nextElement();
System.out.println(s);
}
System.out.println("---------get all headers---------");
//获取所有头
Enumeration names = request.getHeaderNames();
while( names.hasMoreElements() )
{
String name = names.nextElement();
String s = request.getHeader(name);
System.out.println(s);
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
/*******************
其中，html文件如下
带数据给Test2
******************************/
Cookie实现浏览记录（最简陋版本）
主界面代码：
package com.mine;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class Test
*/
@WebServlet("/NewTest")
public class NewTest extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* Default constructor.
*/
public NewTest() {
// 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
// Cookie t[] = request.getCookies();
// for( int i = 0 ; i < t.length ;i++ )
// t[i].setMaxAge(0);
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
//网站已有的商品
List l = MyList.getAll();
out.println("共有"+l.size()+"本书: "+"
");
for( Book book:l )
{
//out.println(book.name+"
");
String name = book.getName();
out.println(" "+name
+""+"
");
}
//浏览过的商品
out.println("浏览过的：");
Cookie cookie[] = request.getCookies();
if( cookie == null )
{
System.out.println("kong");
return;
}
out.println("cookie num: "+cookie.length+"
");
for( Cookie c:cookie )
{
if( c.getName().equals("history") )
{
if( c.getValue().equals("") )
{
c.setMaxAge(0);
System.out.println("remove");
break;
}
//System.out.println("history value: "+c.getValue() );
String names[] = c.getValue().split(",");
for( String s:names )
out.print(s+"
");
break;
}
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}
class MyList
{
static List l;
static
{
l = new ArrayList();
l.add( new Book("Java","123") );
l.add( new Book("C","33") );
l.add( new Book("WEB","93") );
}
static List getAll()
{
return l;
}
}
class Book
{
String name,price;
public Book() {
super();
}
public Book(String name, String price) {
super();
this.name = name;
this.price = price;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getPrice() {
return price;
}
public void setPrice(String price) {
this.price = price;
}
}
显示书籍界面，以及更新cookie
package com.mine;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class Process
*/
@WebServlet("/Process")
public class Process extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public Process() {
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.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
out.println("您要的书籍如下:
");
String name = request.getParameter("name");
Book b=null;
for( Book book:MyList.l )
{
if( book.name.equals(name) )
{
b = book;
break;
}
}
out.println(b.getName());
out.println(b.getPrice());
//更新cookie
Cookie cookie[] = request.getCookies();
boolean haveHistory = false;
if( cookie != null )
for( Cookie c:cookie )
{
if( c.getName().equals("history") )
{
System.out.println("终于找到一个，值 "+c.getValue() );
haveHistory = true;
ArrayList s = mySplit( c.getValue() ); //将split的数组装到ArrayList中
//List s = Arrays.asList(c.getValue().split(","));
//呜呜，其实可以这样写
if( s==null )
break;
boolean in = false;
for( String ss:s )
if( ss.equals(name) ) //浏览记录有这本书
{
in = true;
s.remove(name);
break;
}
if( in ) //如果在记录里，加到最前面，表示最近浏览
s.add(0, name);
else s.add(name);
String value="";
for( String ss:s )
value = value.concat(ss+",");
value = value.substring(0, value.length()-1);
Cookie newCookie = new Cookie("history",value);
newCookie.setMaxAge(30*24*60*60); //设置cookie时限为30天
newCookie.setPath("/CookieSession");
response.addCookie(newCookie);
break;
}
}
else //没有历史记录，就没有这个cookie
{
Cookie newCookie = new Cookie("history", name);
newCookie.setMaxAge(30*24*60*60);
newCookie.setPath("/CookieSession");
response.addCookie(newCookie);
}
}
static ArrayList mySplit( String s )
{
String temp[] = s.split(",");
ArrayList ans = new ArrayList();
for( String ss:temp )
ans.add(ss);
return ans;
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}
}