HttpSession对象的详解与实战操作
HttpSession对象：
HttpSession是当一个用户第一次访问某个网站通过HttoServletRequest中调用getSession方法创建的
1. getSession有俩个重载方法：
getSession()
getSession(boolean create)
getSession(false) 方法返回当前的HttpSession ，若没有，则返回null
getSession(true)方法返回当前的HttpSession，若没有，则创建一个并返回，getSession(true)与getSession()方法一致
2.
HttpSession的setAttribute方法将一个值放在HttpSession对象里
void setAttribute（String name,Object value）
注意：与网址重写，隐藏域不同，放在HttpSession中的值是保存在内存中的。会影响性能
value可以为任意java对象，只要他的类实现了java.io.Serializable接口即可，保存的对象可以序列化成一个文件保存到数据库中
getAttribute方法可以用于获取属性
Object getAttribute(name)
getAttrubuteNames()，他返回一个Enumeration，迭代HttpSession对象的所有属性
3
通过HttpSession中调用getId方法，可以获取HttpSession的标识符
String getId（）
4
在默认情况下，HttpSession对象是在用户静默一段时间之后过期，setMaxInactiveInterval方法可以为个别HttpSession对象的Session设置一个期限
void setMaxInactiveInterval（int seconds）
如果这个方法传入0，则改HttpSession将永远不会过期，直到应用程序卸载或者Servlet容器关闭为止
下面举个例子，这个类实现了一个小型的在线商城，里面有四种商品。它允许用户将商品添加到购物车中，并浏览其内容
//下面为产品类
package appShop;
public class Product {
private int id;//产品id
private String name;//产品名称
private String description;//产品描述
private float price;//产品价格
public Product(int id,String name,String description,float price){
this.setId(id);
this.setName(name);
this.setDescription(description);
this.setPrice(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 appShop;
public class ShoppingItem {
private Product product;
private int quantity;
public ShoppingItem(Product product,int quantity){
this.setProduct(product);
this.setQuantity(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;
}
}
//下面为主类
package appShop;
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 products=new ArrayList();
private NumberFormat currencyFormat=NumberFormat.getCurrencyInstance(Locale.US);
//初始化四种产品包括其细节
@Override
public void init() throws ServletException {
products.add(new Product(1,"TV","LOW-cost from China",159.95F));
products.add(new Product(2,"Player","High quality stylish player",99.95F));
products.add(new Product(3,"System","5 speaker hifi system with ipod",129.95F));
products.add(new Product(4,"iPod player","can paly multiple formats",39.95F));
} //URL都要调用doGet方法，依据URL的后缀启动不同方法，产生不同页面
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String uri=req.getRequestURI();
if(uri.endsWith("/products")){
sendProductList(resp);
}else if(uri.endsWith("/viewProductDetails")){
sendProductDetails(req,resp);
}else if(uri.endsWith("/viewCart")){
showCart(req,resp);
}
}
//当点击buy时，则获取其请求，将产品及其数量放入购物车
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
int quantity=0;
int productId=0;
try{
productId=Integer.parseInt(req.getParameter("id"));
quantity=Integer.parseInt(req.getParameter("quantity"));
}catch(NumberFormatException e){}
Product product=getProduct(productId);
if(product!=null&&quantity>0){
ShoppingItem shoppingItem=new ShoppingItem(product, quantity);
HttpSession session=req.getSession();
List cart=(List) session.getAttribute(CART_ATTRIBUTE);
if(cart==null){
cart=new ArrayList();
session.setAttribute(CART_ATTRIBUTE, cart);
}
cart.add(shoppingItem);
}
//若产品为空，则启动产品列表
sendProductList(resp);
} //发送产品的列表
private void sendProductList(HttpServletResponse response) throws IOException{
response.setContentType("text/html");
PrintWriter write=response.getWriter();
write.println("Products "+
"Products
");
write.println("");
//列出product列表
for(Product product:products){
write.println("- "+product.getName()+"("+currencyFormat.format(product.getPrice())
+") ("+"Details)");
}
write.println("
");
write.println("View Cart");
write.println("");
}
private Product getProduct(int productId) {
for(Product product:products){
if(product.getId()==productId){
return product;
}
}
return null;
} //发送产品描述
private void sendProductDetails(HttpServletRequest req,
HttpServletResponse resp) throws IOException {
resp.setContentType("text/html");
PrintWriter write=resp.getWriter();
int productId=0;
try{
productId=Integer.parseInt(req.getParameter("id"));
}catch(NumberFormatException e){}
Product product =getProduct(productId);
if(product!=null){
write.println(""
+"Product Details "
+"Product Details
"
+"");
}else{
write.println("No product found");
}
} //展示购物车
private void showCart(HttpServletRequest req, HttpServletResponse resp) throws IOException {
resp.setContentType("text/html");
PrintWriter writer=resp.getWriter();
writer.println("Shopping Cart ");
writer.println("Product List");
HttpSession session=req.getSession();
List cart=(List)
session.getAttribute(CART_ATTRIBUTE);
if(cart!=null){
writer.println("");
writer.println(""
+"Quantity "
+"Product "
+"Price "
+"Amount ");
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(""
+""+quantity+" "
+""+product.getName()+" "
+""+currencyFormat.format(price)+" ");
double subtotal=price*quantity;
writer.println(""+currencyFormat.format(subtotal));
total+=subtotal;
writer.println(" ");
}
}
writer.println(""
+"style='text-align:right'>"
+"Total:"
+currencyFormat.format(total)
+"
");
}
writer.println("");
}
}
下面URL时调用应用程序的主页面：
http://localhost:8080/appShop/products (appShop为web项目名称)