局部请求页面不会变化,返回的响应我们要动态获取,获取后选择数据更新区域。
全局请求会更新整个页面例子如下。
@WebServlet("/request")
public class RequestServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse respose) throws ServletException, IOException {respose.getWriter().println("get");直接更新了整个页面}@Overrideprotected void doPost(HttpServletRequest request, HttpServletResponse respose) throws ServletException, IOException {respose.getWriter().println("post");}
}
respose.getWriter().println("get");会将原来的页面销毁掉,重新生成另一张页面,但是在原来的页面中有不需要刷新的页面,我们想要的效果只是小部分区域进行显示刷新出来的内容,这时就要用到Ajax。
[{"empno": "7369",数字可以加双引号也可以不加"ename": "李宁","job": "软件工程师","hiredate": "2015-02-2","salary": 1300,"dname": "研发部"},{"empno": "73691","ename": "李上","job": "软件工程师","hiredate": "2015-02-2","salary": 1300,"dname": "研发部"}
]
JS如何展示json数据利用json数据如下
Title
注意:ajax请求返回的不再与展现相关,而是纯纯的数据,浏览器接受后要考虑如何展示。
两个数据转换核心问题:
数据对象序列化为JSON字符串----JacKson解决序列化问题
JSON字符串如何转换成数据对象--
@WebServlet("/news")
public class NewServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {List list = new ArrayList<>();list.add(new News("TIOBE:2018编程语言排行趋势","2018","TIBOT","...."));list.add(new News("TIOBE:2017编程语言排行趋势","2017","TIBOT","...."));list.add(new News("TIOBE:2016编程语言排行趋势","2016","TIBOT","...."));//序列化过程,可能报错ObjectMapper objectMapper=new ObjectMapper();String json = objectMapper.writeValueAsString(list);response.setContentType("text/json;charset=utf-8");response.getWriter().println(json);}
}
Tomcat配置问题:Warning:The selected directory is not a TomEE home
解决:tomcat选择的时候选错了
错误: 代理抛出异常错误: java.rmi.server.ExportException: Port already in use: 1099; nested exception is:
java.net.BindException: Address already in use: JVM_Bind
解决:端口占用了
解决:中途导入的jar包和依赖没有被out出来,最后允许的目录在Out,如果jar添加了,out没有,那么此时需要手动添加
反序列化过程:
原生的ajax要创建对象,接受并且判断响应,很麻烦,有封装好的。
get方式发送请求:
post方式发送请求:
异步执行代码实例:
结果:send没有收到响应,就执行console.log("请求已经发送");这句话,然后随着状态变化事件得到执行。
结果:当send执行没有结束,没有收到响应,不会执行console.log("请求已经发送");,导致事件状态变化监听失败,所以if必须提前,那么就可以执行相应的语句;
效果
准备数据
@WebServlet("/channel")
public class ChannerServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {//levels为一级目录大类,parent为一级大类的code,这两个都是用户选择的参数//用户根据需要选择一级大类,然后根据用户的选择获取大类的code,再用parent和用户选择的比较,得到二级大类String level=request.getParameter("level");String parent = request.getParameter("parent");List chlist = new ArrayList<>();if (level==null){level = "0";} else if (parent==null) {parent = "0";}if (level.equals("1")) {chlist.add(new Channel("ai","人工智能"));chlist.add(new Channel("web","前端开发"));}else if(level.equals("2")){if (parent.equals("ai")) {chlist.add(new Channel("dl","深度学习"));chlist.add(new Channel("cv","计算机视觉"));chlist.add(new Channel("nlp","自然语言处理"));} else if (parent.equals("web")) {chlist.add(new Channel("html","前端html"));chlist.add(new Channel("css","前端css"));chlist.add(new Channel("js","前端js"));}}ObjectMapper objectMapper = new ObjectMapper();String json = objectMapper.writeValueAsString(chlist);response.setContentType("application/json;charset=utf-8");response.getWriter().println(json);}
}
实体类:
public class Channel {private String code;private String name;public Channel(String code, String name) {this.code = code;this.name = name;}public String getCode() {return code;}public void setCode(String code) {this.code = code;}public String getName() {return name;}public void setName(String name) {this.name = name;}
}
前端界面发送请求:
Title
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