跨域访问的两种解决方式：jsonp和cors

1. JSONP
   jsonp详解的参考网页
   JSONP的最基本的原理是：动态添加一个

$.ajax({
    url : "test!test.action",
    type : "GET",
    data : ({}),
    dataType : "jsonp",
    jsonp: 'jsonpcallback', 
    ......
    });

服务端代码 返回的格式为：jsonpCallback({msg:’this is json data’}) 。参考代码如下：

String jsoncallback = getFromRequest("jsonpcallback");
return (jsoncallback+"({\"rlt\":\"", SUCCESS, "\"})");

1. CORS
   CORS参考网页
   修改tomcat下CORS（ 跨域 资源共享） 的配置 :
   首先下载cors-filter-1.7.jar，property-utils-1.9.jar这两个库文件，放到tomcat的lib目录下。
   其次修改web.xml

<filter>
    <filter-name>CORS</filter-name>
    <filter-class>com.thetransactioncompany.cors.CORSFilter</filter-class>
        <init-param>
            <param-name>cors.allowOrigin</param-name>
            <param-value>*</param-value>
        </init-param>
        <init-param>
            <param-name>cors.supportedMethods</param-name>
            <param-value>GET, POST, HEAD, PUT, DELETE</param-value>
        </init-param>
        <init-param>
            <param-name>cors.supportedHeaders</param-name>
    <param-value>Accept, Origin, X-Requested-With, Content-Type, Last-Modified</param-value>
        </init-param>
        <init-param>
            <param-name>cors.exposedHeaders</param-name>
            <param-value>Set-Cookie</param-value>
        </init-param>
        <init-param>
            <param-name>cors.supportsCredentials</param-name>
            <param-value>true</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>CORS</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>