AJAX应该如何发送请求

XMLHttpRequest对象

XMLHttpRequest对象的方法

方法描述abort()取消当前请求getAllResponseHeaders()返回头部信息getResponseHeader()返回特定的头部信息open(method, url, async, user, psw)规定请求method：请求类型 GET 或 POSTurl：文件位置async：true（异步）或 false（同步）user：可选的用户名称psw：可选的密码send()将请求发送到服务器，用于 GET 请求send(string)将请求发送到服务器，用于 POST 请求setRequestHeader()向要发送的报头添加标签/值对 属性描述onreadystatechange定义当 readyState 属性发生变化时被调用的函数readyState保存 XMLHttpRequest 的状态。0：请求未初始化 1：服务器连接已建立 2：请求已收到 3：正在处理请求 4：请求已完成且响应已就绪responseText以字符串返回响应数据responseXML以 XML 数据返回响应数据status返回请求的状态号200: "OK"403: "Forbidden"404: “Not Found”statusText返回状态文本（比如 “OK” 或 “Not Found”）

AJAX GET请求

@WebServlet("/ajaxRequest")
 public class AjaxRequestServlet extends HttpServlet {@Overrideprotected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {PrintWriter out = response.getWriter();//XMLHttpRequest对象获取输出信息out.print("welcome to study ajax");}
 }
 

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AJAX POST请求

模拟form的post请求

 用户名：
密码：

 
 
 

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JSON

Connection conn = null;PreparedStatement ps = null;ResultSet rs = null;ArrayList arrayList = new ArrayList<>();response.setContentType("text/html;charset=UTF-8");PrintWriter out = response.getWriter();try {conn = DbUtil.getConnection();String sql = "select * from stu";ps = conn.prepareStatement(sql);rs = ps.executeQuery();while (rs.next()) {String name = rs.getString("name");int age = rs.getInt("age");String address = rs.getString("address");Student student = new Student(name, age, address);arrayList.add(student);}out.print(JSON.toJSONString(arrayList));
 //前提是创建好User对象
 

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XML

基于XML的小例子

 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.setContentType("text/xml;charset=UTF-8");PrintWriter out = response.getWriter();StringBuilder str = new StringBuilder();str.append("");str.append("");str.append("zhangsan");str.append("18");str.append("
北京
");str.append("");str.append("");str.append("lisi");str.append("18");str.append("
上海
");str.append("");str.append("");out.print(str);}
 

 window.onload = function (){document.getElementById("btn").onclick = function (){var xhr = new XMLHttpRequest();xhr.onreadystatechange = function (){if (this.readyState ===4){if (this.status ===200){var stuDOC = this.responseXML;//返回一个xml对象var students = stuDOC.getElementsByTagName("Student")var html = ""for (let i = 0; i < students.length; i++) {html += ""var stu = students[i]var childNodes = stu.childNodes;html +=""+(i+1)+""for (let j = 0; j < childNodes.length; j++) {var node = childNodes[j]if (node.nodeName === "name"){html += ""+node.textContent+""}if(node.nodeName ==="age"){html += ""+node.textContent+""}if(node.nodeName ==="address"){html += ""+node.textContent+""}}html += ""}console.log(html)document.getElementById("stubody").innerHTML = html}else {alert("error")}}}xhr.open("GET","/ajax/g",true)xhr.send()}
 

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AJAX乱码问题

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 ---## AJAX乱码问题- - 对于tomcat9来说呢？- 响应中文的时候，会出现乱码，怎么解决？```javaresponse.setContentType("text/html;charset=UTF-8");```- 发送ajax post请求的时候，发送给服务器的数据，服务器接收之后乱码，怎么解决？```javarequest.setCharacterEncoding("UTF-8");```---## AJAX的异步与同步