java 服务器端解决跨域问题

现在很多开发的 API 都支持 ajax 直接请求，这样就会导致跨域的问题，解决跨域的问题一方面可以从前端，另一方面就是服务器端。

   一、Controller类名上方添加@CrossOrigin 注解通过此方式注解则Controller中的所有通过@RequestMapping注解的方法都可以进行跨域请求。 代码如下：

    @CrossOrigin()
    @RequestMapping("/demoController")
    @Controller
    public class DemoController {
    @Autowired
    IDemoService demoService;

    @RequestMapping(value = "/test", method = RequestMethod.POST)
    @ResponseBody
    public ResultModel test(HttpServletRequest request)
            throws Exception {
        return “right”;
    }
}

二、让所有的controller类继承自定义的BaseController类,该类中将对返回的头部做些特殊处理。

public abstract class BaseController {
  /**
     * description:send the ajax response back to the client side
     * @param responseObj
     * @param response
     */
    protected void writeAjaxJSONResponse(Object responseObj, HttpServletResponse response) {
        response.setCharacterEncoding("UTF-8");

        response.setHeader("Cache-Control", "no-cache, no-store, must-revalidate"); // HTTP 1.1
        response.setHeader("Pragma", "no-cache"); // HTTP 1.0

        /**
         * for ajax-cross-domain request TODO get the ip address from
         * configration(ajax-cross-domain.properties)
         */
        response.setHeader("Access-Control-Allow-Origin", "*");

        response.setDateHeader("Expires", 0); // Proxies.

        PrintWriter writer = getWriter(response);

        writeAjaxJSONResponse(responseObj, writer);
    }
  /**
     *
     * @param response
     * @return
     */
    protected PrintWriter getWriter(HttpServletResponse response) {
        if(null == response){
            return null;
        }

        PrintWriter writer = null;

        try {
            writer = response.getWriter();
        } catch (IOException e) {
            logger.error("unknow exception", e);
        }

        return writer;
    }

    /**
     * description:send the ajax response back to the client side.
     *
     * @param responseObj
     * @param writer
     * @param writer
     */
    protected void writeAjaxJSONResponse(Object responseObj, PrintWriter writer) {
        if (writer == null || responseObj == null) {
            return;
        }
        try {         writer.write(JSON.toJSONString(responseObj,SerializerFeature.DisableCircularReferenceDetect));
        } finally {
            writer.flush();
            writer.close();
        }
    }
}
接下来就是我们自己业务的 controller 了，其中主要是要调用 writeAjaxJSONResponse(result, response); 这个方法
@Controller
@RequestMapping(value = "/account")
public class AccountController extends BaseController {
@RequestMapping(value = "/add", method = RequestMethod.POST)
    public void addAccount(HttpSession session,HttpServletRequest request,HttpServletResponse response){
        ViewerResult result = new ViewerResult();
         //实现自己业务逻辑代码
        writeAjaxJSONResponse(result, response);
    }

}
好了，这种简单的方式就实现了。

三、Filter,我们在写springMVC的时候，更喜欢的方式是通过@ResponseBody给返回对象进行封装直接返回给前端，这样简单而且容易。  如果使用@ResponseBody就不能使用第一种方法了，所有就使用filter给所有的请求都封装一下跨域，接下来直接实现代码：

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

public class HeadersCORSFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse servletResponse,
            FilterChain chain) throws IOException, ServletException {
         HttpServletResponse response = (HttpServletResponse) servletResponse;
            response.setHeader("Access-Control-Allow-Origin", "*");
            response.setHeader("Access-Control-Allow-Methods", "POST, GET, OPTIONS, DELETE");
            response.setHeader("Access-Control-Max-Age", "3600");
            response.setHeader("Access-Control-Allow-Headers", "x-requested-with,Authorization");
            response.setHeader("Access-Control-Allow-Credentials","true");
            chain.doFilter(request, servletResponse);

    }

    @Override
    public void destroy() {
        // TODO Auto-generated method stub

    }

}
好了，filter 实现了，然后就是要在 web.xml 里面把这个 filter 运用起来了。
打开项目的 web.xml，填写下面的几行代码：

cors
      xxx.xxxx.xxxxx.xxxx.HeadersCORSFilter
    
      cors
      /open/*
    
好了，通过上面的3种方式，可以解决百分之80的跨域问题，也许还有更好的解决方案，可以提出来大家一起学习学习。
最好的方案是最符合当前需求且易于扩展的。