HttpSession物件的詳解與實戰操作
阿新 • • 發佈：2019-01-10
HttpSession物件：
HttpSession是當一個使用者第一次訪問某個網站通過HttoServletRequest中呼叫getSession方法建立的
1. getSession有倆個過載方法：
getSession()
getSession(boolean create)
getSession(false) 方法返回當前的HttpSession ，若沒有，則返回null
getSession(true)方法返回當前的HttpSession，若沒有，則建立一個並返回，getSession(true)與getSession()方法一致
2.
HttpSession的setAttribute方法將一個值放在HttpSession物件裡
void setAttribute（String name,Object value）
注意：與網址重寫，隱藏域不同，放在HttpSession中的值是儲存在記憶體中的。會影響效能
value可以為任意java物件，只要他的類實現了java.io.Serializable介面即可，儲存的物件可以序列化成一個檔案儲存到資料庫中
getAttribute方法可以用於獲取屬性
Object getAttribute(name)
getAttrubuteNames()，他返回一個Enumeration，迭代HttpSession物件的所有屬性
3
通過HttpSession中呼叫getId方法，可以獲取HttpSession的識別符號
String getId（）
4
在預設情況下，HttpSession物件是在使用者靜默一段時間之後過期，setMaxInactiveInterval方法可以為個別HttpSession物件的Session設定一個期限
void setMaxInactiveInterval（int seconds）
如果這個方法傳入0，則改HttpSession將永遠不會過期，直到應用程式解除安裝或者Servlet容器關閉為止
下面舉個例子，這個類實現了一個小型的線上商城，裡面有四種商品。它允許使用者將商品新增到購物車中，並瀏覽其內容
//下面為產品類
package appShop;
public class Product {
private int id;//產品id
private String name;//產品名稱
private String description;//產品描述
private float price;//產品價格
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;
}
}
//下面為主類
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<Product> products=new ArrayList<Product>();
private NumberFormat currencyFormat=NumberFormat.getCurrencyInstance(Locale.US);
//初始化四種產品包括其細節
@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都要呼叫doGet方法，依據URL的字尾啟動不同方法，產生不同頁面
@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);
}
}
//當點選buy時，則獲取其請求，將產品及其數量放入購物車
@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<ShoppingItem> cart=(List<ShoppingItem>) session.getAttribute(CART_ATTRIBUTE);
if(cart==null){
cart=new ArrayList<ShoppingItem>();
session.setAttribute(CART_ATTRIBUTE, cart);
}
cart.add(shoppingItem);
}
//若產品為空，則啟動產品列表
sendProductList(resp);
} //傳送產品的列表
private void sendProductList(HttpServletResponse response) throws IOException{
response.setContentType("text/html");
PrintWriter write=response.getWriter();
write.println("<html><head><title>Products</title>"+
"</head><body><h2>Products</h2>");
write.println("<ul>");
//列出product列表
for(Product product:products){
write.println("<li>"+product.getName()+"("+currencyFormat.format(product.getPrice())
+") ("+"<a href='viewProductDetails?id="+product.getId()+"'>Details</a>)");
}
write.println("</ul>");
write.println("<a href='viewCart'>View Cart</a>");
write.println("</body></html>");
}
private Product getProduct(int productId) {
for(Product product:products){
if(product.getId()==productId){
return product;
}
}
return null;
} //傳送產品描述
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("<html><head>"
+"<title>Product Details</title></head>"
+"<body><h2>Product Details</h2>"
+"<form method='post' action='addToCart'>");
write.println("<input type='hidden' name='id' "
+"value=' "+productId+" '/>");
write.println("<table>");
write.println("<tr><td>Name:</td><td>"
+product.getName()+"</td></tr>");
write.println("<tr><td>Description:</td><td>"
+product.getDescription()+"</td></tr>");
write.println("<tr>"+"<tr>"
+"<td><input name='quantity' ></td>"
+"<td><input type='submit' value='buy'></td>"
+"</tr>");
write.println("<tr><td colspan='2'>"
+"<a href='products'>Product List</a>"
+"</td></tr>");
write.println("</table>");
write.println("</form></body>");
}else{
write.println("No product found");
}
} //展示購物車
private void showCart(HttpServletRequest req, HttpServletResponse resp) throws IOException {
resp.setContentType("text/html");
PrintWriter writer=resp.getWriter();
writer.println("<html><head><title>Shopping Cart</title></head>");
writer.println("<body><a href='products'>Product List</a>");
HttpSession session=req.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>Amount</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>"
+"<td>"+quantity+"</td>"
+"<td>"+product.getName()+"</td>"
+"<td>"+currencyFormat.format(price)+"</td>");
double subtotal=price*quantity;
writer.println("<td>"+currencyFormat.format(subtotal));
total+=subtotal;
writer.println("</tr>");
}
}
writer.println("<tr><td colspan='4'>"
+"style='text-align:right'>"
+"Total:"
+currencyFormat.format(total)
+"</td></tr>");
writer.println("</table>");
}
writer.println("</table></body></html>");
}
}
下面URL時呼叫應用程式的主頁面：
http://localhost:8080/appShop/products (appShop為web專案名稱)