java中默认返回一个值怎么设置

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信息小飞侠 2024-09-07 09:35:27

文章标签 java中默认返回一个值怎么设置 jquery 实例 java 前端 文章分类 Java 后端开发

今天是复习jQuery的最后一天，基本常用技术已全部练习，以后遇到不会的可查文档。总的来说，jQuery的出现，在写前端代码时省事了好多。

one.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
	<head>
		<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
		<script type="text/javascript" src="<c:url value='/js/jquery-3.1.0.js' />"></script>
		<title>jQuery技术实例</title>
		<script type="text/javascript">
			$(function(){
				$("#btn1").click(function(){
					//jQuery-ajax的get方法是不能传递中文的参数，否则会乱码
					var url="<c:url value='/Servlet1' />";
					$.get(url,{"name":"AA中文","age":22},function(data,textStatus,xhr){
						alert(data+","+textStatus);
					});//格式：jQuery.get(url, [data], [callback], [type])  最后一个参数为空
				});
				$("#btn2").click(function(){
					//jQuery-ajax的普通post方法是可以传递中文参数
					var url="<c:url value='/Servlet1' />";
					$.post(url,{"name":"AAAA中文","age":22},function(data,textStatus,xhr){
						alert(data+","+textStatus);//可正常显示后台发来的信息
					});//格式：jQuery.post(url, [data], [callback], [type])  最后一个参数为空
				});
				$("#btn3").click(function(){
					//jQuery-ajax的post---xml方法通信
					var url="<c:url value='/Servlet1' />";
					$.post(url,{"name":"AAAA中文","age":22},function(data,textStatus,xhr){
						//alert(data+","+textStatus);//object XMLDocument
						//jQuery来解析xml格式的dom对象
						//<users><user id='U001'><name>jack1</name><name>jack2</name></user><user id='U002'><name>Tom</name></user></users>"
						$(data).find("user").each(function(){
							//for循环遍历   获取当前user对象的id
							var id=$(this).attr("id");
							//alert(id);
							
							//获取当前<user>的name
							var name=$(this).find("name:eq(0)").text();//这种方式能实现一个user中有两个name，只显示一个name
							
							alert(id+","+name);
						});
						
					},"xml");//post方法最后一个参数表示通信方式返回内容格式，xml, html, script, json, text, _default。

				});
				
				$("#btn4").click(function(){
				//jQuery-ajax的post---json方法通信技术	
					var url="<c:url value='/JsonServlet3' />";
					$.post(url,{"name":"AAAA中文","age":22},function(data,textStatus,xhr){
						//alert(data);  //json-object  有很多object(这里是user对象)
						
						$(".d").empty();//先清空已经显示的内容
						$.each(data,function(idx,val){
							$(".d").append(idx+":"+val.id+","+val.name+","+val.age+"<br/>");
							
						});
						
					},"json");//指定json通信
				});
				
			});
		
		</script>
	</head>
	<body>
		<button id="btn1">jQuery-ajax的get方法技术</button><br/>
		<button id="btn2">jQuery-ajax的post方法技术</button><br/>
		<button id="btn3">jQuery-ajax的post---xml方法通信技术</button><br/>
		<button id="btn4">jQuery-ajax的post---json方法通信技术</button><br/>
		<div class="d"></div>
		<br/><hr/>
		<a href="<c:url value='/MenuServlet' />">点击进入动态(从数据库)加载二级菜单 jQuery中ajax.load()方法</a>
	</body>
</html>

Servlet1.java

package cn.hncu.servlet;

import java.io.IOException;
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("/Servlet1")
public class Servlet1 extends HttpServlet {
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		System.out.println("get方式的请求来了....");//不支持中文
		String name = request.getParameter("name");
		String age = request.getParameter("age");
		System.out.println("name:"+name+",age:"+age);
		response.setContentType("text/html;charset=utf-8");
		String str ="<users><user id='U001'><name>jack</name></user>"
				         + "<user id='U002'><name>Tom</name></user></users>";
		response.getWriter().print(str);
		
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		System.out.println("post方式的请求来了....");
		request.setCharacterEncoding("utf-8");
		String name = request.getParameter("name");
		String age = request.getParameter("age");
		System.out.println("name:"+name+",age:"+age);
		response.setContentType("text/html;charset=utf-8");
		String str ="<users><user id='U001'><name>jack1</name><name>jack2</name></user>"
				         + "<user id='U002'><name>Tom</name></user></users>";
		response.getWriter().print(str);
	}

}

JsonServlet3

package cn.hncu.servlet;

import java.io.IOException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
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 com.alibaba.fastjson.JSON;

import cn.hncu.domain.User;

@WebServlet("/JsonServlet3")
public class JsonServlet3 extends HttpServlet {
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		doPost(request, response);
	}
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		System.out.println("post-json方式的请求来了....");
		request.setCharacterEncoding("utf-8");
		String name = request.getParameter("name");
		String age = request.getParameter("age");
		System.out.println("name:"+name+",age:"+age);
		
		//按理应该调用service、dao层并从数据库中把数据读取出来，这里模拟了...
		List<User> users = new ArrayList<User>();
		users.add( new User("U001","Jack",22));
		users.add( new User("U010","张三",12));
		users.add( new User("U002","Rose",23));
		request.setAttribute("users", users);

		//利用fastjson的工具为我们把后台的List<User>类型的数据封装成json格式串，发送前端
		//json串格式: [{name:"Jack",id:"U001",age:22},{...},{...}]
		//转List-json※※※
		String json = JSON.toJSONString(users);
		System.out.println("json:"+json);
		
		//转Map-json
		Map<String, Object> map = new HashMap<String, Object>();
		map.put("addr", "湖南");
		map.put("id", "P001");
		map.put("sex", "男");
		map.put("age", 20);
		map.put("friend", new User("U001","Jack",22));
		String str = JSON.toJSONString(map);
		System.out.println(str);
		
		//发给前端
		response.setCharacterEncoding("utf-8");
		response.getWriter().print(json);
	}

}

这里是实现了ajax get和post通信，jQuery中有封装好的的ajax通信，直接调用方法即可，不再用写底层代码了。

java中默认返回一个值怎么设置_java

MenuServlet.java

注：此处用到了C3p0和QueryRunner，它的配置文件和工具类这里就不再贴出了。以前的博客有详细介绍。

package cn.hncu.servlet;

import java.io.IOException;
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;

import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;

import cn.hncu.domain.Menu;
import cn.hncu.utils.DataSourceUtils;
import cn.hncu.utils.QueryRunner;

@WebServlet("/MenuServlet")
public class MenuServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//查询出所有一级菜单
		String sql="select * from menus where parent is null";
		QueryRunner run=new QueryRunner(DataSourceUtils.getDataSource());
		List<Menu> menus=run.query(sql, new BeanListHandler<Menu>(Menu.class));
		System.out.println(menus);
		request.setAttribute("menus", menus);
		request.getRequestDispatcher("/three/two.jsp").forward(request, response);
	}
	
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//加载主菜单下面的二级菜单
		String id=request.getParameter("pid");
		String sql="select * from menus where parent="+id;
		QueryRunner run=new QueryRunner(DataSourceUtils.getDataSource());
		List<Menu> menus=run.query(sql, new BeanListHandler<Menu>(Menu.class));
		request.setAttribute("subMenus", menus);
		request.getRequestDispatcher("/three/three.jsp").forward(request, response);
	}

}

two.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
	<head>
		<style type="text/css">
		 	#menu{
		 		border: 1px solid red;
			 	width: 40%;
			 	background:gray;
			 	margin:3px;
			 	cursor:pointer;
		    }
		    .main{
		    	height:60px;
		    	background:gray;
		    	border: 1px solid blue;
		    	width: 20%;
		    	margin:15px;
		    	cursor: pointer;
		    }
		    .sub{
		    	background:yellow;
		    	width: 40%;
		    	margin:3px;
		    }
		</style>
		<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
		<script type="text/javascript" src="<c:url value='/js/jquery-3.1.0.js' />"></script>
		<title>jQuery技术实例</title>
		<script type="text/javascript">
			$(function(){
				$(".main").click(function(){
					var sub=$(this).next(".sub");
					if(sub.length>0){
						sub.toggle();
					}else{
						var subDiv=$("<div class='sub' >AAAA</div>");//利用jQuery核心函数创建出一个jQuery对象，然后调用jQuery中的函数
						var url="<c:url value='/MenuServlet' />";
						var id=$(this).attr("id");
						subDiv.load(url,{pid:id});//把通过load加载的内容放到subDiv中
						$(this).after(subDiv);//加在主菜单后面----兄弟关系
					}
				});
			});
		
		</script>
	</head>
	<body>
		<b>以下是菜单</b>
		<div id="menu">
			<c:forEach items="${menus}" var="menu">
				<div class="main" id="${menu.id}">
					<p align="center">${menu.name}</p>
				</div>
			</c:forEach>
		</div>
	</body>
</html>

three.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"
	pageEncoding="UTF-8"%>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<c:forEach items="${subMenus}" var="menu">
	<a href="<c:url value='${menu.url}'/>">${menu.name}</a> <br/>
</c:forEach>

sql记录

CREATE TABLE menus(
id INT PRIMARY KEY,
NAME VARCHAR(30),
parent INT,
url VARCHAR(100)
); 

INSERT INTO menus VALUES(1,"管理员",NULL,NULL);
INSERT INTO menus VALUES(2,"一般管理员",NULL,NULL);
INSERT INTO menus VALUES(3,"管理用户",1,'/jsps/1.jsp');
INSERT INTO menus VALUES(4,"管理图书",1,'/BookSevlet');
INSERT INTO menus VALUES(5,"管理订单",2,'/BookSevlet');
INSERT INTO menus VALUES(6,"管理出货",2,'/BookSevlet');

这也算是一个小小的应用吧。可根据数据库中的记录来查找一级菜单和二级菜单。

java中默认返回一个值怎么设置_jquery_02