标签：servlet not rcu public buffer ble 分享 urlencode 开始
一、概述
AJAX全称Asynchronous JavaScript And XML，是一种创建交互式网页应用的开发技术。
在浏览器上的AJAX程序可以在不重新加载整个页面的情况下，以异步的方式与服务器通信并只更新页面的一部分。
其原理是通过浏览器的XHR对象向服务器发送异步请求并接收服务器的响应数据，然后通过JS操作DOM来实现动态局部刷新。
简单说AJAX是HTML/CSS/JS/XHR的集合。
二、XHR
AJAX的核心技术是XHR（即XMLHttpRequest），是浏览器的内置对象。其主要作用是在后台与服务器交换数据，该对象主要用于网页的局部刷新。
XHR可以在不向服务器提交整个页面的情况下，实现页面的局部刷新。当页面加载完毕后，客户端通过该对象向服务器请求数据，再接收服务器的响应数据。
XHR可以同步或异步地返回服务器响应，并以文本或DOM的形式返回内容。
XHR提供了一系列属性用于访问该对象的具体参数。
1.readyState属性用于描述对象的当前状态：(readyState的变化触发onreadystatechange事件）
| 数值 | 描述 |
| 0 | XHR对象已建立但未初始化 |
| 1 | 服务器连接已建立 |
| 2 | 请求已发送但未收到响应 |
| 3 | 请求处理中但只接收了部分数据 |
| 4 | 请求已经完成且响应已就绪 |
2.responeText属性用于保存响应信息，与readyState的变化同步。
3.responeXML属性用于保存XML形式的响应数据，在请求完成之前为null。
4.status属性描述了HTTP的状态，仅当请求已经开始处理后才能获取。
| 状态码 | 描述 |
| 200 | OK |
| 304 | 缓存 |
| 403 | 无权限 |
| 404 | Not Found |
| 501 | 服务器级别错误 |
5.statusText属性为status属性的状态代码文本，同样仅当请求处理开始后才能获取。
XHR提供的方法主要用于初始化和处理HTTP请求。
三、实例
处理GET请求。
//index.jsp <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ page isELIgnored="false" %> <html> <body> <script language="JavaScript"> function getXHR() { let req = new XMLHttpRequest(); req.onreadystatechange = function () { if (req.readyState === 4 && req.status === 200) { document.getElementById("ajax-test").innerText = req.responseText; } }; req.open("GET", "MyServlet?text=Hello World!", true); req.send(); } </script> <input type="button" value="GET" onclick="getXHR()"> <div id="ajax-test"></div> </body> </html> //MyServlet.java package servlet; 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 java.io.IOException; @WebServlet(urlPatterns = "/MyServlet") public class MyServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String reqText = req.getParameter("text"); String respText = reqText.toUpperCase(); resp.getWriter().write(respText); } }
处理POST请求。
//index.jsp <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ page isELIgnored="false" %> <html> <head> <script> function postXHR() { let req = new XMLHttpRequest(); req.onreadystatechange = function () { if (req.readyState === 4 && req.status === 200) { document.getElementById("ajax-test").innerHTML = req.responseText; } }; let name = document.getElementById("name").value; let pass = document.getElementById("pass").value; req.open("POST", "MyServlet", true); let params = "name=" + name + "&pass=" + pass; req.setRequestHeader("Content-type", "application/x-www-form-urlencoded"); req.send(params); } </script> </head> <body> 用户：<input type="text" id="name" placeholder=""><br/> 密码：<input type="password" id="pass" placeholder=""><br/> <input type="button" value="提交" onclick="postXHR()"><br/> <div id="ajax-test"></div> </body> </html> //MyServlet.java package servlet; 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 java.io.IOException; import java.io.PrintWriter; @WebServlet(urlPatterns = "/MyServlet") public class MyServlet extends HttpServlet { @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String name = req.getParameter("name"); String pass = req.getParameter("pass"); PrintWriter out = resp.getWriter(); out.write(String.format("User: %s<br/>", name)); out.write(String.format("Pass: %s<br/>", pass)); } }
获取XML形式响应。
//index.jsp <%@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ page isELIgnored="false" %> <html> <head> </head> <body> <script language="JavaScript"> function loadXMLDoc() { let req = new XMLHttpRequest(); req.onreadystatechange = function () { if (req.readyState === 4 && req.status === 200) { let nodes = req.responseXML.getElementsByTagName("student"); let str = ""; for (let i = 0; i < nodes.length; i++) { str += nodes[i].getAttribute("id") + ": " + nodes[i].childNodes[1].textContent + "<br/>"; } document.getElementById("ajax-test").innerHTML = str; } }; req.open("GET", "MyServlet", true); req.send(); } loadXMLDoc(); </script> <div id="ajax-test"></div> </body> </html> //test.xml <?xml version="1.0" encoding="UTF-8" ?> <class> <student id="30"> <name>Stephen Curry</name> </student> <student id="35"> <name>Kevin Durant</name> </student> <student id="11"> <name>Klay Tompson</name> </student> <student id="23"> <name>Draymond Green</name> </student> <student id="0"> <name>DeMarcus Cousins</name> </student> </class> //MyServlet.java package servlet; 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 java.io.File; import java.io.FileInputStream; import java.io.IOException; @WebServlet(urlPatterns = "/MyServlet") public class MyServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { File doc = new File("C:\\Users\\User\\IdeaProjects\\Project\\web\\WEB-INF\\test.xml"); byte[] buffer = new byte[(int) doc.length()]; try (FileInputStream in = new FileInputStream(doc)) { int size = in.read(buffer); System.out.println("XML Bytes: " + size); } String content = new String(buffer); System.out.println("XML Content:\n" + content); resp.setContentType("text/xml;charset=UTF-8"); resp.getWriter().write(content); } }
标签：servlet not rcu public buffer ble 分享 urlencode 开始
原文地址：https://www.cnblogs.com/arseneyao/p/9400478.html
