一、引入jquery文件

<script src="${ctx}/static/js/jquery-1.12.4.min.js"></script>

二、请求方式

$.ajax({
    type: "GET",
    data: {},
    dataType: "JSON",
    contentType: "application/json;charset=UTF-8",
    async: false,
    url: "${ctx}/system/menu",
    success: function (data) {
        var html = "";
        html += "<ul class='catalogue-menu'>";
        for (var i = 0; i < data.length; i++) { // 一级菜单
            html += "<li class='catalogue-menu-li'>" +
                "<a class='catalogue-menu-first' target='_blank' href='" + data[i].url + " '>"
                + data[i].name + "</a>";

            html += "<div class='menu-panel hide'>";
            html += "<div class='menu-classifies'>";

            for (var j = 0; j < data[i].menus.length; j++) { // 二级菜单
                html += "<div class='classifies-second'>";
                html += "<div class='domestic'>";
                html += "<a href=' " + data[i].menus[j].url + " ' target='_blank'>" + data[i].menus[j].name + "</a>";
                html += "</div>";

                html += "<div class='classifies-third'>";
                html += " <ul>";

                for (var k = 0; k < data[i].menus[j].menus.length; k++) { // 三级菜单
                    html += "<li>";
                    html += "|";
                    html += "<a href='" + data[i].menus[j].menus[k].url + " ' target='_blank'" +
                        "title='" + data[i].menus[j].menus[k].name + " '>";
                    html += data[i].menus[j].menus[k].name;
                    html += "</a>";
                    html += "</li>";
                }
                html += "<li>&nbsp;</li>";
                html += "</ul>";
                html += "</div>";
                html += "</div>";
            }
            html += "</div>";
            html += "</div>";
            html += "</li>";
        }
        html += "</ul>";
        $("#menu").html(html);
    }, error:(data) => { 
       服务器没有返回数据,方法返回值void,抛异常等
    }
});

三、解决跨域访问

crossDomain: true; -> 前端ajax请求属性
httpServletResponse.setHeader("Access-Control-Allow-Origin", "*"); -> 后端设置

四、请求时携带cookie

xhrFields: {
    withCredentials: true -> 前端ajax请求属性
}

String origin = httpServletRequest.getHeader("Origin"); -> 后端设置
if (StringUtils.isEmpty(origin)) {
    origin = httpServletRequest.getHeader("Referer");
}
httpServletResponse.setHeader("Access-Control-Allow-Origin", origin);
httpServletResponse.setHeader("Access-Control-Allow-Credentials", "true");

if (RequestMethod.OPTIONS.toString().equals(httpServletRequest.getMethod())) {
    String allowMethod = httpServletRequest.getHeader("Access-Control-Request-Method");
    String allowHeaders = httpServletRequest.getHeader("Access-Control-Request-Headers");
    httpServletResponse.setHeader("Access-Control-Max-Age", "86400"); -> 浏览器缓存预检请求结果时间,单位:秒
    httpServletResponse.setHeader("Access-Control-Allow-Methods", allowMethod); ->允许浏览器在预检请求成功之后发送的实际请求方法名
    httpServletResponse.setHeader("Access-Control-Allow-Headers", allowHeaders); ->允许浏览器发送的请求消息头
}

检测请求来源为ajax,如果ajax设置了跨域属性crossDomain,请求头将会消失(无法检测)
if ("XMLHttpRequest".equals(httpServletRequest.getHeader("X-Requested-With"))) {
  String url = httpServletRequest.getScheme() + "://" + httpServletRequest.getServerName() + ":" + httpServletRequest.getServerPort() + httpServletRequest.getContextPath();
  httpServletResponse.setHeader("REDIRECT", "REDIRECT");
  httpServletResponse.setHeader("CONTENTPATH", url + "/login.html");
  httpServletResponse.setStatus(HttpServletResponse.SC_FORBIDDEN);
} else {
    String url = httpServletRequest.getContextPath() + "/login.html";
    httpServletResponse.sendRedirect(url);
}

多个异步任务执行完成后再执行下面操作
$.when(ajax1,ajax2,ajax3).done(function(){
    完成时回调
}).fail(function () {
    失败时回调
});

$.when(ajax1,ajax2,ajax3).then(done(),fail());

五、AJAX跳转页面

window.location.href = url + "/login.html"; -> 当前页面路径跳转某个页面路径
window.location.replace(document.referrer); -> 跳转到上一个页面并刷新
window.location.reload(); -> 重新加载当前页
history.back(); -> 浏览器点击后退按钮效果
history.forward(); -> 浏览器点击前进按钮效果
history.go(index); -> 综合前进后退效果,正数向前,负数想后

六、跳转到上一个页面

function historyGoBack() {
    if ((navigator.userAgent.indexOf('MSIE') >= 0) && (navigator.userAgent.indexOf('Opera') < 0)) { // IE
        if (history.length > 0) {
            window.location.replace(document.referrer);
        } else {
            window.location.href = url+"/main.html";
        }
    } else { //非IE浏览器
        if (navigator.userAgent.indexOf('Firefox') >= 0 ||
            navigator.userAgent.indexOf('Opera') >= 0 ||
            navigator.userAgent.indexOf('Safari') >= 0 ||
            navigator.userAgent.indexOf('Chrome') >= 0 ||
            navigator.userAgent.indexOf('WebKit') >= 0) {

            if (window.history.length > 1) {
                if (document.referrer.indexOf("/register.html") > -1) {
                    window.location.href = url+"/main.html";
                } else {
                    window.location.replace(document.referrer);
                }
            } else {
                 window.location.href= url+"/main.html";
            }
        } else { //未知的浏览器
            window.location.replace(document.referrer);
        }
    }
}

通过window.location.href获取当前页面路径,以参数的方式传给后台方法,
登录成功后,在控制器中通过重定向跳转到该参数路径的页面。

注意事项：在浏览器访问的地址和在ajax中的访问地址必须完全一样，否则会出现获取不到cookie的结果。ajax请求里面嵌套ajax请求，请求方式需要设置为同步，否则在ajax结果回调前，已经执行下面的代码。

七、获取URL的参数

var parseUrl = function () { -> 普通URL
    var searchHref = window.location.search.replace('?', '');
    var params = searchHref.split('&');
    var returnParam = {};
    params.forEach(function(param) {
      var paramSplit = param.split('=');
      returnParam[paramSplit[0]] = paramSplit[1];
    });
    return returnParam;
}

var parseUrl = function() { -> 特殊符号URL
    var index = window.location.href.indexOf('?');
    var href = window.location.href.substr((index+1));
    var params = href.split('&');
    var returnParam = {};
    params.forEach(function(param) {
        var paramSplit = param.split('=');
        returnParam[paramSplit[0]] = paramSplit[1];
    });
    return returnParam;
}