java web用于保持状态的4种方法

方法一:网址重写

通过在url地址后面添加若干的token作为查询字符串来实现。token的值一般为 键=值

    url?key1=value1&key2=value2&...&keyn=valuen

url与token之间需要用?分开,两个token之间则是需要用一个&符号隔开。

此方法适用于token不需要在多个页面中使用时使用。

缺点是

a.在某些浏览器当中url长度有限制

b.url中的信息是可见的,安全性差

c.某些字符需要进行编码

package com.SessionManage.Test;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

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

@WebServlet(name = "Top10Servlet", urlPatterns = {"/top10"})
public class Top10Servlet extends HttpServlet {
	private static final long serialVersionUID = 987654321L;

	private List<String> londonAttractions;
	private List<String> parisAttractions;
	@Override
	public void init() throws ServletException {
		londonAttractions = new ArrayList<String>(10);
		londonAttractions.add("Buckingham Palace");
		londonAttractions.add("London Eye");
		londonAttractions.add("British Museum");
		londonAttractions.add("National Gallery");
		londonAttractions.add("Big Ben");
		londonAttractions.add("Tower of London");
		londonAttractions.add("Natural History Museum");
		londonAttractions.add("Canary Wharf");
		londonAttractions.add("2012 Olympic Park");
		londonAttractions.add("St Paul‘s Cathedral");

		parisAttractions = new ArrayList<String>(10);
		parisAttractions.add("Eiffel Tower");
		parisAttractions.add("Notre Dame");
		parisAttractions.add("The Louvre");
		parisAttractions.add("Champs Elysees");
		parisAttractions.add("Arc de Triomphe");
		parisAttractions.add("Sainte Chapelle Church");
		parisAttractions.add("Les Invalides");
		parisAttractions.add("Musee d‘Orsay");
		parisAttractions.add("Montmarte");
		parisAttractions.add("Sacre Couer Basilica");
	}

	@Override
	public void doGet(HttpServletRequest request,HttpServletResponse response)
		throws ServletException,IOException{
		String city = request.getParameter("city");
		if(city!=null&&(city.equals("london")||city.equals("paris"))){
			showAttractions(request,response,city);
		}else{
			showMainPage(request,response);
		}
	}

	private void showMainPage(HttpServletRequest request,
			HttpServletResponse response) throws IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		writer.print("<html><head>"
				+ "<title>Top 10 Tourist Attractions</title>"
				+ "</head><body>"
				+"please select a city:"
				+"<br/><a href=‘?city=london‘>London</a>"
				+"<br/><a href=‘?city=paris‘>Paris</a>"
				+"</body></html>");
	}

	private void showAttractions(HttpServletRequest request,
			HttpServletResponse response, String city) throws ServletException,IOException {
		// TODO Auto-generated method stub
		int page = 1;
		String pageParameter = request.getParameter("page");
		if(pageParameter!=null){
			try{
				page = Integer.parseInt(pageParameter);
			}catch(NumberFormatException e){
				e.printStackTrace();
			}
			if(page>2){
				page = 1;
			}
		}
		List<String> attractions = null;
		if(city.equals("london")){
			attractions = londonAttractions;
		}else if(city.equals("paris")){
			attractions = parisAttractions;
		}
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		writer.println("<html><head>"
				+"<title>Top 10 Tourist Attractions</title>"
				+"</head><body>");
		writer.println("<a href=‘top10‘>Select City</a>");
		writer.println("<hr/>Page"+page+"<hr/>");

		int start = page*5-5;
		for(int i = start; i < start+5; i++){
			writer.println(attractions.get(i)+"<br/>");
		}
		writer.print("<hr style=‘color:blue‘/>"
				+ "<a href=‘?city="+city
				+"&page=1‘>Page 1</a>");
		writer.print(" <a href=‘?city="
				+city+"&page=2‘>Page 2</a>");
		writer.println("</body></html>");

	}
}

  方法二:隐藏域

主要适用于页面当中含有表单的情况,当用户提交表单时,隐藏域中的值也传送到服务器。只有当页面包含表单,或者可以在页面添加表单时,才适合使用隐藏域。

此技术胜过网址重写的地方在于可以将更多的字符传递到服务器,且不需要进行字符编码。但仅当所需传递的信息不需要跨越多个页面时,才适合使用这种技术。

package com.SessionManage.Test2;

public class Customer {
	private int id;
	private String name;
	private String city;
	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 getCity() {
		return city;
	}
	public void setCity(String city) {
		this.city = city;
	}

}

  

package com.SessionManage.Test2;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

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

@WebServlet(name = "CustomerServlet",urlPatterns = {
		"/customer","/editCustomer","/updateCustomer"})
public class CustomerServlet extends HttpServlet {
	private static final long serialVersionUID = -20L;
	private List<Customer> customers = new ArrayList<Customer>();

	@Override
	public void init() throws ServletException{
		Customer customer1 = new Customer();
		customer1.setId(1);
		customer1.setName("Donald D.");
		customer1.setCity("Miami");
		customers.add(customer1);

		Customer customer2 = new Customer();
		customer2.setId(2);
		customer2.setName("Mickey M.");
		customer2.setCity("Orlando");
		customers.add(customer2);
	}

	private void sendCustomerList(HttpServletResponse response)
		throws IOException {
			response.setContentType("text/html");
			PrintWriter writer = response.getWriter();
			writer.println("<html><head><title>Customer</title></head>"
					+"<body><h2>Customers </h2>");
			writer.println("<ul>");
			for(Customer customer : customers){
				writer.println("<li>"+customer.getName()
						+"("+customer.getCity()+") "
						+"<a href=‘editCustomer?id="+customer.getId()
						+"‘>edit</a>");
			}
			writer.println("</ul>");
			writer.println("</body></html>");
	}

	private Customer getCustomer(int customerId){
		for(Customer customer : customers){
			if(customer.getId()==customerId){
				return customer;
			}
		}
		return null;
	}

	private void sendEditCustomerForm(HttpServletRequest request,HttpServletResponse response)
									throws IOException {
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		int customerId = 0;
		try{
			customerId = Integer.parseInt(request.getParameter("id"));
		}catch(NumberFormatException e){
			e.printStackTrace();
		}
		Customer customer = this.getCustomer(customerId);
		if(customer!=null){
			writer.println("<html><head>"
					+"<title>Edit Customer</title></head>"
					+"<body><h2>EditCustomer<h2>"
					+"<form method=‘post‘"
					+"action=‘updateCustomer‘>");
			writer.println("<input type=‘hidden‘ name=‘id‘ value=‘"
					+customerId+"‘/>");
			writer.println("<table>");
			writer.println("<tr><td>Name:</td><td>"
					+"<input name=‘name‘ value=‘"
					+customer.getName().replaceAll("‘", "‘")
					+"‘/></td></tr>");
			writer.println("<tr><td>City:</td><td>"
					+"<input name=‘city‘ value=‘"
					+customer.getCity().replaceAll("‘", "‘")
					+"‘/></td></tr>");
			writer.println("<tr>"
					+"<td colspan=‘2‘ style=‘text-align:right‘>"
					+"<input type=‘submit‘ value=‘Update‘/></td>"
					+"</tr>");
			writer.println("<tr><td colspan=‘2‘>"
					+"<a href=‘customer‘>Customer List</a>"
					+"</td></tr>");
			writer.println("</table>");
			writer.println("</form></body>");
		}else{
			writer.println("No customer found");
		}
	}

	@Override
	public void doGet(HttpServletRequest request,HttpServletResponse response)
					throws ServletException, IOException {
		String uri = request.getRequestURI();
		if(uri.endsWith("/customer")){
			this.sendCustomerList(response);
		}else if(uri.endsWith("/editCustomer")){
			this.sendEditCustomerForm(request, response);
		}
	}

	@Override
	public void doPost(HttpServletRequest request,HttpServletResponse response)
						throws ServletException, IOException{
		int customerId = 0;
		try{
			customerId = Integer.parseInt(request.getParameter("id"));
		}catch(NumberFormatException e){
			e.printStackTrace();
		}
		Customer customer = this.getCustomer(customerId);
		if(customer!=null){
			customer.setName(request.getParameter("name"));
			customer.setCity(request.getParameter("city"));
		}
		this.sendCustomerList(response);
	}
}

方法三:cookie

cookie信息可以跨越多个页面,这点是采用网址重写和隐藏域所无法实现的。cookie是自动在web服务器和浏览器之间传递的一小块信息。

cookie适用于那些需要跨越许多页面的信息。因为cookie是作为http标头嵌入的,因此传输它的过程由http协议处理。此外,可以根据自

己的需要设置cookie的有效期限。对于web浏览器而言,每台web服务器最多可以支持20个cookie。

cookie的不足之处是用户可以通过修改其浏览器设置来拒绝接受cookie。

关于cookie的代码如下:

package com.SessionManage.Test3;

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

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;

@WebServlet(name="PreferenceServlet",urlPatterns={"/preference"})
public class PreferenceServlet extends HttpServlet {
	private static final long serialVersionUID = 888L;

	public static final String MENU =
			"<div style=‘background:#e8e8e8;"
			+"padding:15px‘>"
			+"<a href=‘cookieClass‘>Cookie Class</a>  "
			+"<a href=‘cookieInfo‘>Cookie Info</a>  "
			+"<a href=‘preference‘>Preference</a>"+"</div>";
	@Override
	public void doGet(HttpServletRequest request,HttpServletResponse response)
					throws ServletException,IOException{
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		writer.print("<html><head>"+"<title>Preference</title>"
					+"<style>table{"+"font-size:small;"
					+"background:NavajoWhite}</style>"
					+"</head><body>"
					+MENU
					+"Please select the values below:"
					+"<form method=‘post‘>"
					+"<table>"
					+"<tr><td>Title Font Size:</td>"
					+"<td><select name=‘titleFontSize‘>"
					+"<option>large</option>"
					+"<option>x-large</option>"
					+"<option>xx-large</option>"
					+"</select></td>"
					+"</tr>"
					+"<tr><td>Title Style & Weight:</td>"
					+"<td><select name=‘titleStyleAndWeight‘ multiple>"
					+"<option>italic</option>"
					+"<option>bold</option>"
					+"</select></td>"
					+"</tr>"
					+"<tr><td>Max. Records in Table: </td>"
					+"<td><select name=‘maxRecords‘>"
					+"<option>5</option>"
					+"<option>10</option>"
					+"</select></td>"
					+"</tr>"
					+"<tr><td rowspan=‘2‘>"
					+"<input type=‘submit‘ value=‘Set‘/></td>"
					+"</tr>"
					+"</table>"+"</form>"+"</body></html>");
	}

	@Override
	public void doPost(HttpServletRequest request,HttpServletResponse response)
						throws ServletException,IOException{
		String maxRecords = request.getParameter("maxRecords");
		String[] titleStyleAndWeight = request.getParameterValues("titleStyleAndWeight");
		String titleFontSize = request.getParameter("titleFontSize");
		response.addCookie(new Cookie("maxRecords",maxRecords));
		response.addCookie(new Cookie("titleFontSize",titleFontSize));

		Cookie cookie = new Cookie("titleFontWeight","");
		cookie.setMaxAge(0);
		response.addCookie(cookie);

		cookie = new Cookie("titleFontStyle","");
		cookie.setMaxAge(0);
		response.addCookie(cookie);

		if(titleStyleAndWeight!=null){
			for(String style : titleStyleAndWeight){
				if(style.equals("bold")){
					response.addCookie(new Cookie("titleFontWeight","bold"));
				}else if(style.equals("italic")){
					response.addCookie(new Cookie("titleFontStyle","italic"));
				}
			}
		}
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		writer.println("<html><head>"+"<title>Preference</title>"
					+"</head><body>"+MENU
					+"Your preference has been set."
					+"<br/><br/>Max. Records in Table: "+maxRecords
					+"<br/>Title Font Size: "+titleFontSize
					+"<br/>Title Font Style & Weight: ");
		if(titleStyleAndWeight!=null){
			writer.println("<ul>");
			for(String style : titleStyleAndWeight){
				writer.print("<li>"+style+"</li>");
			}
			writer.println("</ul>");
		}
		writer.println("</body></html>");
	}
}

  

package com.SessionManage.Test3;

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

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;

@WebServlet(name="CookieClassServlet",urlPatterns={"/cookieClass"})
public class CookieClassServlet extends HttpServlet{
	private static final long serialVersionUID = 837369L;

	private String[] methods = {
			"clone","getComment","getDomain",
			"getMaxAge","getName","getPath",
			"getSecure","getValue","getVersion",
			"isHttpOnly","setComment","setDomain",
			"setHttpOnly","setMaxAge","setPath",
			"setSecure","setValue","setVersion"
	};

	public void doGet(HttpServletRequest request,HttpServletResponse response)
					throws ServletException,IOException{
		Cookie[] cookies = request.getCookies();
		Cookie maxRecordsCookie = null;
		if(cookies!=null){
			for(Cookie cookie : cookies){
				if(cookie.getName().equals("maxRecords")){
					maxRecordsCookie = cookie;
					break;
				}
			}
		}

		int maxRecords = 5;
		if(maxRecordsCookie!=null){
			try{
				maxRecords = Integer.parseInt(maxRecordsCookie.getValue());
			}catch(NumberFormatException e){
				e.printStackTrace();
			}
		}

		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		writer.print("<html><head>"+"<title>Cookie Class</title>"
					+"</head><body>"
					+PreferenceServlet.MENU
					+"<div>Here are some of the methods in "+
					"javax.servlet.http.Cookie");
		writer.print("<ul>");

		for(int i = 0;i < maxRecords; i++){
			writer.print("<li>"+methods[i]+"</li>");
		}
		writer.print("</ul>");
		writer.print("</div></body></html>");
	}
}

  

package com.SessionManage.Test3;

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

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 javax.ws.rs.core.Cookie;

@WebServlet(name="CookieInfoServlet",urlPatterns={"/cookieInfo"})
public class CookieInfoServlet extends HttpServlet {
	private static final long serialVersionUID = 3829L;

	@Override
	public void doGet(HttpServletRequest request,HttpServletResponse response)
					throws ServletException,IOException{
		javax.servlet.http.Cookie[] cookies = request.getCookies();
		StringBuilder styles = new StringBuilder();
		styles.append(".title{");
		if(cookies!=null){
			for(javax.servlet.http.Cookie cookie : cookies){
				String name = cookie.getName();
				String value = cookie.getValue();
				if(name.equals("titleFontSize")){
					styles.append("font-size:"+value+";");
				}else if(name.equals("titleFontWeight")){
					styles.append("font-weight:"+value+";");
				}else if(name.equals("titleFontStyle")){
					styles.append("font-style:"+value+";");
				}
			}
		}
		styles.append("}");
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		writer.print("<html><head>"+"<title>Cookie Info</title>"
					+"<style>"+styles.toString()+"</style>"
					+"</head><body>"+PreferenceServlet.MENU
					+"<div class=‘title‘>"
					+"Session Management with Cookies:</div>");
		writer.print("<div>");

		if(cookies==null){
			writer.print("No cookie in this Http response");
		}else{
			writer.println("<br/>Cookie in this Http response");
			for(javax.servlet.http.Cookie cookie : cookies){
				writer.println("<br/>"+cookie.getName()+":"+cookie.getValue());
			}
		}
		writer.print("</div>");
		writer.print("</body></html>");
	}
}

方法四:HttpSession对象

用户可以没有或者有一个HttpSession,并且只能访问自己的HttpSession。HttpSession是当一个用户第一次访问某个站点时创建的。通过request中getSession()方法,可以获取用户的HttpSession。而通过HttpSession的setAttribut(name,value)方法可以将值放入到HttpSession当中。

同网址重写、隐藏域和cookie所不同的地方在于,放在HttpSession中的值是保存在内存中的。因此,你只能将尽可能小的对象放在里面,并且数量不能太多。

添加到HttpSession当中的值不一定是String,可以为任意的java对象,只要它的类实现了java.io.Serializable接口即可,以便当Servlet容器认为有必要的时候,保存的对象可以序列化成一个文件或者保存到数据库中。

setAttribute方法要求不同的对象有不同的名称。如果传递一个之前用过的属性名称,那么该名称将与旧值无关联,而与新值关联。

通过HttpSession的getAttribute(name)属性可以获取HttpSession中保存的对象。其另外一个方法getAttributeNames()返回一个Enumeration,迭代一个HttpSession中的

所有属性。

注:HttpSession中保存的值不发送到客户端,这与其它的Session管理方法不同。而是Servlet容器为它所创建的每一个HttpSession生成一个唯一标示符,并将这个标示符作为一个token发送给浏览器,一般是作为一个名为JSESSIONID的cookie,或者作为一个jsessionid参数添加到url后面。在后续的请求中,浏览器会将这个token发送回服务器,使服务器知道是哪个用户在发出请求。

相关代码如下:

package com.SessionManage.Test4;

public class Product {
	private int id;
	private String name;
	private String description;
	private float price;

	public Product(int id,String name,String description,float price){
		this.id = id;
		this.name = name;
		this.description = description;
		this.price = price;
	}

	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 getDescription() {
		return description;
	}

	public void setDescription(String description) {
		this.description = description;
	}

	public float getPrice() {
		return price;
	}

	public void setPrice(float price) {
		this.price = price;
	}

}

  

package com.SessionManage.Test4;

public class ShoppingItem {
	private Product product;
	private int quantity;

	public ShoppingItem(Product product,int quantity){
		this.product = product;
		this.quantity = quantity;
	}

	public Product getProduct() {
		return product;
	}

	public void setProduct(Product product) {
		this.product = product;
	}

	public int getQuantity() {
		return quantity;
	}

	public void setQuantity(int quantity) {
		this.quantity = quantity;
	}

}

  

package com.SessionManage.Test4;

import java.io.IOException;
import java.io.PrintWriter;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;

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 javax.servlet.http.HttpSession;

@WebServlet(name="ShoppingCartServlet",urlPatterns={"/products","/viewProductDetails",
		"/addToCart","/viewCart"
})
public class ShoppingCartServlet extends HttpServlet {
	private static final long serialVersionUID = -20L;
	private static final String CART_ATTRIBUTE = "cart";

	private List<Product> products = new ArrayList<Product>();
	private NumberFormat currencyFormat = NumberFormat.getCurrencyInstance(Locale.US);

	@Override
	public void init() throws ServletException{
		products.add(new Product(1,"Bravo 32‘ HDTV","Low-cost HDTV from renowned TV manufacturer",159.95F));
		products.add(new Product(2,"Bravo BluRay Player","High quality stylish BluRay player",99.95F));
		products.add(new Product(3,"Bravo Stereo System","5 speaker hifi system with iPod player",129.95F));
		products.add(new Product(4,"Bravo iPod player","An iPod plug-in that can play multiple formats",39.95F));
	}

	@Override
	public void doGet(HttpServletRequest request,HttpServletResponse response)
					throws ServletException,IOException{
		String uri = request.getRequestURI();
		if(uri.endsWith("/products")){
			sendProductList(response);
		}else if(uri.endsWith("/viewProductDetails")){
			sendProductDetail(request,response);
		}else if(uri.endsWith("/viewCart")){
			showCart(request,response);
		}
	}

	@Override
	protected void doPost(HttpServletRequest request,HttpServletResponse response)
					throws ServletException,IOException{
		int productId = 0;
		int quantity = 0;
		try{
			productId = Integer.parseInt(request.getParameter("id"));
			quantity = Integer.parseInt(request.getParameter("quantity"));
		}catch(NumberFormatException e){
			e.printStackTrace();
		}
		Product product = getProduct(productId);
		if(product!=null&&quantity>=0){
			ShoppingItem shoppingItem = new ShoppingItem(product,quantity);
			HttpSession session = request.getSession();
			List<ShoppingItem> cart = (List<ShoppingItem>)session.getAttribute(CART_ATTRIBUTE);
			if(cart==null){
				cart = new ArrayList<ShoppingItem>();
				session.setAttribute(CART_ATTRIBUTE, cart);
			}
			cart.add(shoppingItem);
		}
		sendProductList(response);
	}

	private Product getProduct(int productId) {
		// TODO Auto-generated method stub
		for(Product product : products){
			if(product.getId()==productId){
				return product;
			}
		}
		return null;
	}

	private void showCart(HttpServletRequest request,
			HttpServletResponse response) throws IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		writer.println("<html><head><title>Shopping Cart</title>"
						+"</head>");
		writer.println("<body><a href=‘products‘>"
						+"Product List</a>");
		HttpSession session = request.getSession();
		List<ShoppingItem> cart = (List<ShoppingItem>)session.getAttribute(CART_ATTRIBUTE);
		if(cart!=null){
			writer.println("<table>");
			writer.println("<tr><td style=‘width:150px‘>Quantity"
							+"</td>"
							+"<td style=‘width:150px‘>Product</td>"
							+"<td style=‘width:150px‘>Price</td>"
							+"<td>Amout</td></tr>");
			double total = 0.0;
			for(ShoppingItem shoppingItem : cart){
				Product product = shoppingItem.getProduct();
				int quantity = shoppingItem.getQuantity();
				if(quantity!=0){
					float price = product.getPrice();
					writer.println("<tr>");
					writer.println("<td>"+quantity+"</td>");
					writer.println("<td>"+product.getName()+"</td>");
					writer.println("<td>"+currencyFormat.format(price)+"</td>");
					double subtotal = price*quantity;
					writer.println("<td>"+currencyFormat.format(subtotal)+"</td>");
					total += subtotal;
					writer.println("</tr>");
				}
			}
			writer.println("<tr><td colspan=‘4‘"
							+"style=‘text-align:right‘>"
							+"Total:"
							+currencyFormat.format(total)
							+"</td></tr>");
		}
		writer.println("</table></body></html>");
	}

	private void sendProductDetail(HttpServletRequest request,
			HttpServletResponse response) throws IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		int productId = 0;
		try{
			productId = Integer.parseInt(request.getParameter("id"));
		}catch(NumberFormatException e){
			e.printStackTrace();
		}
		Product product = this.getProduct(productId);

		if(product!=null){
			writer.println("<html><head>"
							+"<title>Product Details</title></head>"
							+"<body><h2>Product Details</h2>"
							+"<form method=‘post‘ action=‘addToCart‘>");
			writer.println("<input type=‘hidden‘ name=‘id‘ "
							+"value=‘"+productId+"‘/>");
			writer.println("<table>");
			writer.println("<tr><td>Name:</td><td>"
							+product.getName()+"</td></tr>");
			writer.println("<tr><td>Description:</td><td>"
							+product.getDescription()+"</td></tr>");
			writer.println("<tr>"+"<tr>"
							+"<td><input name=‘quantity‘/></td>"
							+"<td><input type=‘submit‘ value=‘Buy‘/>"
							+"</td>"
							+"</tr>");
			writer.println("<tr><td colspan=‘2‘>"
							+"<a href-‘products‘>Product List</a>"
							+"</td></tr>");
			writer.println("</table>");
			writer.println("</form></body>");
		}else{
			writer.println("No product found");
		}

	}

	private void sendProductList(HttpServletResponse response) throws IOException {
		// TODO Auto-generated method stub
		response.setContentType("text/html");
		PrintWriter writer = response.getWriter();
		writer.println("<html><head><title>Products</title>"
						+"</head><body><h2>Products</h2>");
		writer.println("<ul>");
		for(Product product :products){
			writer.println("<li>"+product.getName()+"("
							+currencyFormat.format(product.getPrice())
							+") ("+"<a href=‘viewProductDetails?id="
							+product.getId()+"‘>Details</a>)");
		}
		writer.println("</ul>");
		writer.println("<a href=‘viewCart‘>View Cart</a>");
		writer.println("</body></html>");
	}
}

  

时间: 2024-10-10 07:24:14

java web用于保持状态的4种方法的相关文章

Java解析XML文件的四种方法

[摘要] 可扩展标志语言(XML)在实现信息标准化.信息的交流与共享上有其独特的技术优势,因此受到了广泛的重视.本文先简单的介绍了XML基本知识,然后从XML应用入手总结了四种现今最常见的XML的解析方法,介绍了这四种方法的特点,其中包括优点与不足之处.最后给出了一个简单的案例来对这四种解析进行代码介绍. [关键字] XML文件,DOM,SAX,JDOM,DOM4J [引言] XML即可扩展标记语言(EXtensible Markup Language),是标准通用标记语言的子集,是一种用于标记

java连接sql server2008的两种方法

最近学到java连接数据库(sql server),发现常用的我们有两种方法,那么这里我总结一下这两种方法怎么使用,还有它们的区别,还有我们一般要使用哪一种方法. 方法一:使用jdbc-odbc桥连接sql server,作为中间媒介连接数据库; 注意我们每次在连接数据库前都必须要引入sql包:import java.sql.*;接下来的步骤都是习惯性步骤,我这里就按照每一步的使用进行列举: 1.配置数据源:打开控制面版->管理工具->数据源(ODBC)->(一般而言我们使用用户DSN)

Java 计算中英文长度的若干种方法

在项目开发中经常碰到到输入字符的校验,特别是中英文混合在一起的校验.而为了满足校验的需求,有时需要计算出中英文的长度. 本文将通过几种常用的方法实现长度的计算: <span style="font-size:18px;">import java.io.UnsupportedEncodingException; /** * 中英文校验的处理 * @author a123demi * */ public class EnChValidate { public static vo

java中遍历MAP的几种方法

java中遍历MAP的几种方法 Java代码 Map<String,String> map=new HashMap<String,String>();    map.put("username", "qq");    map.put("passWord", "123");    map.put("userID", "1");    map.put("em

Java实现ping功能的三种方法

Java实现ping功能的三种方法 检测设备的运行状态,有的是使用ping的方式来检测的.所以需要使用java来实现ping功能. 为了使用java来实现ping的功能,有人推荐使用java的 Runtime.exec()方法来直接调用系统的Ping命令,也有人完成了纯Java实现Ping的程序,使用的是Java的NIO包(native io, 高效IO包).但是设备检测只是想测试一个远程主机是否可用.所以,可以使用以下三种方式来实现: 1.Jdk1.5的InetAddresss方式 自从Jav

(转)java向MySQL插入当前时间的四种方式和java时间日期格式化的几种方法(案例说明)

java向MySQL插入当前时间的四种方式和java时间日期格式化的几种方法(案例说明);部分资料参考网络资源 1. java向MySQL插入当前时间的四种方式 第一种:将java.util.Date类型的时间转成mysql数据库识别的java.sql.Date类型时间 注:java.util.Date是java.sql.Date的父类 Date time= new java.sql.Date(newjava.util.Date().getTime()); 第二种: java用PreparedS

Java web 常见对象的取值方法整理

一.从request中取值: 1.取param: servlet:  request.getParameter() request.getParameterValues() jsp脚本:request.getParameter() request.getParameterValues() jstl/el:  ${param.name} ${paramaValues.names[0]} struts ognl:<s:property value="#parameters.ParamName[

java向MySQL插入当前时间的四种方式和java时间日期格式化的几种方法(案例说明)

java向MySQL插入当前时间的四种方式和java时间日期格式化的几种方法(案例说明);部分资料参考网络资源 1. java向MySQL插入当前时间的四种方式 第一种:将java.util.Date类型的时间转成mysql数据库识别的java.sql.Date类型时间 注:java.util.Date是java.sql.Date的父类 Date time= new java.sql.Date(newjava.util.Date().getTime()); 第二种: java用PreparedS

关于java获取本地ip的几种方法

关于java获取本地ip的几种方法1.获取本地ip的方法 System.out.println(InetAddress.getLocalHost().getHostAddress()); 2.域名解析ip的方法 System.out.println(InetAddress.getByName("www.sina.com.cn")); 3.获取本地出口ip的方法(局域网NAT或本地找交换机出口ip的方法) 建立通讯TCP,telnet,mina通讯等. Socket client = n