package com.gomall.action; import java.io.IOException; import java.io.PrintWriter; import java.util.Date; 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.codehaus.jackson.map.ObjectMapper; import com.gomall.bean.Product; import com.gomall.service.IProductService; import com.gomall.service.ProductService; @WebServlet("/Product") public class ProductAction extends HttpServlet { private static final long serialVersionUID = 1L; public ProductAction() { super(); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { /*模拟网络延时*/ try { Thread.sleep(3000); } catch (InterruptedException e) { e.printStackTrace(); } request.setCharacterEncoding("utf-8"); response.setCharacterEncoding("utf-8"); String act = request.getParameter("act"); IProductService productService = new ProductService(); /**用于序列化json*/ ObjectMapper mapper = new ObjectMapper(); PrintWriter out=response.getWriter(); if (act.equals("getAll")) { String json = mapper.writeValueAsString(productService.getAll()); out.append(json); } else if (act.equals("area")) { String callback=request.getParameter("callback"); out.append(callback+"('"+new Date()+"')"); } else if (act.equals("getJSONP")) { String callback=request.getParameter("callback"); String json = mapper.writeValueAsString(productService.getAll()); out.append(callback+"("+json+")"); } else if (act.equals("getAllCORS")) { /**向响应的头部中添加CORS信息*/ response.addHeader("Access-Control-Allow-Origin", "*"); response.addHeader("Access-Control-Allow-Methods", "GET,POST"); String json = mapper.writeValueAsString(productService.getAll()); out.append(json); } else if(act.equals("del")){ /**向响应的头部中添加CORS信息*/ response.addHeader("Access-Control-Allow-Origin", "*"); response.addHeader("Access-Control-Allow-Methods", "GET,POST"); int id=Integer.parseInt(request.getParameter("id")); String json = mapper.writeValueAsString(productService.deleteById(id)); out.append(json); } else if(act.equals("add")){ /**向响应的头部中添加CORS信息*/ response.addHeader("Access-Control-Allow-Origin", "*"); response.addHeader("Access-Control-Allow-Methods", "GET,POST"); String name=request.getParameter("name"); double price=Double.parseDouble(request.getParameter("price")); String detail=request.getParameter("detail"); Product entity=new Product(0, name, price, "",detail); String json = mapper.writeValueAsString(productService.add(entity)); out.append(json); } } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }
运行结果：
删除：
二、延迟对象（Deferred）
deferred对象就是jQuery1.5版以后新增加的回调函数解决方案。
2.1、回调函数
先看一个示例：
首先，为什么要使用Deferred？
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>回调</title> </head> <body> <script src="https://www.jb51.net/js/jQuery1.11.3/jquery-1.11.3.min.js" type="text/javascript" charset="utf-8"></script> <script type="text/javascript"> var student; $.get("student.json",function(data){ student=data; },"json"); alert(student); </script> </body> </html>
student.json文件：{"name":"tom","id":"01"}
运行结果：
因为AJAX是异步执行的，类似高级语言中的多线程，当发起ajax请求时会有网络延迟，而代码并没有在$.get的位置被阻塞，alert先执行，但数据并没有从远程获取到，所以结果是undefined。
其实初学者经常会犯这种错误，如：
function getStudentById(id){ $.get("students.do",{"id":id},function(stu){ return stu; },"json"); }
上面的代码是有问题的，原因如前面的示例是一样的。怎么解决，如果你认为是异步带来的问题，当然通过同步是可以解决的，如：
$.ajax({ type:"get", url:"student.json", async:false, /*非异步，同步*/ success:function(data){ student=data; } });
结果：
如果将所有的ajax请求修改为同步的，则ajax的好处就大打折扣了，如果即要异步又要解决上面的问题，可以使用回调方法。
示例：