肿么把json返回的数据显示到html页面上?

给你一个大致的方案，具体想要实现的方法自己解决，不懂再问。
先要导入这两个包：
script type=text/javascript src=js/jquery.js/script
script type=text/javascript src=js/json.js/script
input type=button value=使用Json请求去后台获取数据返回是json对象 onClick=toJson();
function toJson()
{
/*发出是json请求：返回的字符串是json对的字符串*/
$.getJSON(jsonViewServlet?falg=2,null,function call(data){jsonResponse(data);});
}

我这里java代码是用servlet实现：
if (2.equals(flag)) {
JSONObject resultJSON = new JSONObject();
try {
resultJSON.put(sex, 男);
resultJSON.put(age, 22);
resultJSON.put(name, 张三);
System.out.println(resultJSON.toString()); /* {sex:男,name:张三,age:22} */
} catch (Exception e) {
e.printStackTrace();
}
out.print(resultJSON.toString());
}
在web.xml里面怎么配置servlet就不需要我多说了吧？

一般都是后台直接拼接好JSON格式返回，页面解析。
给你看个例子：
%@ page language=java contentType=text/html; charset=GB18030
pageEncoding=GB18030%
!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=GB18030
title四级联动下拉列表选中值保持不变/title
style type=text/css
div #tip {
font:consolas normal 20px;
color:blue;
}
/style
script type=text/javascript src=js/jquery-1.4.4.min.js/script
script type=text/javascript
$(function() {
$(#province).change(function() {
if ($(#province).val() == '0') {
$(#city).html('');
$(#county).html('');
$(#town).html('');
return;
}
$(#tip).append(span请求Ajax获取城市...br/span);
$.get(ajax.do,
{type:'1',
value:$(#province).val(),
time:new Date()
},function(data) {
$(#tip).append(span+$(#province).val()+下城市信息获取成功br/span);
$(#city).html('option value=0 selected=selected请选择一个市/option');
var pros = eval(data);
for (var i=0;ipros.length;i++) {
var cityName = pros[i].name;
var cityValue = pros[i].value;
var opt = $(option value=' + cityValue + '+cityName+/option);
$(#city).append(opt);
}
});
});
$(#city).change(function() {
$(#tip).append(span请求Ajax获取县...br/span);
if ($(#city).val() == '0') {
$(#county).html('');
$(#town).html('');
return;
}
$.get(ajax.do,
{type:'2',
value:$(#city).val(),
time:new Date()
},function(data) {
$(#tip).append(span+$(#city).val()+下县的信息获取成功br/span);
$(#county).html('option value=0 selected=selected请选择一个县/option');
var pros = eval(data);
for (var i=0;ipros.length;i++) {
var countyName = pros[i].name;
var countyValue = pros[i].value;
var opt = $(option value=' + countyValue + '+countyName+/option);
$(#county).append(opt);
}
});
});
$(#county).change(function() {
$(#tip).append(span请求Ajax获取镇...br/span);
if ($(#county).val() == '0') {
$(#town).html('');
return;
}
$.get(ajax.do,
{type:'3',
value:$(#county).val(),
time:new Date()
},function(data) {
$(#tip).append(span+$(#county).val()+下镇的信息获取成功br/span);
$(#town).html('');
var pros = eval(data);
for (var i=0;ipros.length;i++) {
var townName = pros[i].name;
var townValue = pros[i].value;
var opt = $(option value=' + townValue + '+townName+/option);
$(#town).append(opt);
}
});
});
});
/script
/head
body
省：select id=province
option value=0 selected=selected请选择一个省/option
option value=hubei湖北/option
/select
市：select id=city/select
县：select id=county/select
镇：select id=town/select

div id=tip/div
/body
/html

package com.servlet.ajax;
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;

/**
* Servlet implementation class AjaxServlet
*/
@WebServlet(/ajax.do)
public class AjaxServlet extends HttpServlet {
private static final long serialVersionUID = 1L;

/**
* Default constructor.
*/
public AjaxServlet() {
// TODO Auto-generated constructor stub
}

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
this.doPost(request, response);
}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType(text/html;charset=utf-8);
String type = request.getParameter(type);
String value = request.getParameter(value);
PrintWriter pw = response.getWriter();
System.out.println(type);

if (1.equals(type) && value != null && !.equals(value)) { // 根据省获取市
// 这里可以从数据库获取
if (hubei.equals(value)) {
StringBuilder citys = new StringBuilder();
citys.append([);
citys.append({name:'武汉',value:'hubei001'},);
citys.append({name:'襄阳',value:'hubei002'});
citys.append(]);
System.out.println(citys.toString());
pw.print(citys.toString());
}
}
else if (2.equals(type) && value != null && !.equals(value)) { // 根据省获取县
// 这里可以从数据库获取
StringBuilder countries = new StringBuilder();
if (hubei001.equals(value)) {
countries.append([);
countries.append({name:'AAA县',value:'wuhan001'},);
countries.append({name:'BBB县',value:'wuhan002'},);
countries.append({name:'CCC县',value:'wuhan003'});
countries.append(]);
}
else if (hubei002.equals(value)) {
countries.append([);
countries.append({name:'南漳县',value:'xiangyang001'},);
countries.append({name:'古城县',value:'xiangyang002'});
countries.append(]);
}

System.out.println(countries.toString());
pw.print(countries.toString());
}
else if (3.equals(type) && value != null && !.equals(value)) {
StringBuilder towns = new StringBuilder();

if (wuhan001.equals(value)) {
towns.append([);
towns.append({name:'AAA镇',value:'wuhan001'},);
towns.append({name:'BBB镇',value:'wuhan002'},);
towns.append({name:'CCC镇',value:'wuhan003'});
towns.append(]);

}
else if (wuhan002.equals(value)) {
towns.append([);
towns.append({name:'CCC镇',value:'wuhan001'},);
towns.append({name:'DDD镇',value:'wuhan002'},);
towns.append({name:'EEE镇',value:'wuhan003'});
towns.append(]);
}
else if (wuhan003.equals(value)) {
towns.append([);
towns.append({name:'FFF镇',value:'wuhan001'},);
towns.append({name:'GGG镇',value:'wuhan002'});
towns.append(]);
}
else if (xiangyang001.equals(value)) {
towns.append([);
towns.append({name:'WWW镇',value:'wuhan001'},);
towns.append({name:'RRR镇',value:'wuhan002'});
towns.append(]);
}
else if (xiangyang002.equals(value)) {
towns.append([);
towns.append({name:'XXX镇',value:'wuhan001'},);
towns.append({name:'YYY镇',value:'wuhan002'});
towns.append(]);
}

System.out.println(towns.toString());
pw.print(towns.toString());
}
}

}