Java后台判断ajax请求及处理过程详解

import java.io.IOException; 
import java.io.PrintWriter; 
 
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.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
 
import org.slf4j.Logger; 
import org.slf4j.LoggerFactory; 
import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.stereotype.Component; 
 
 
 
@Component("authenticationFilter") 
public class AuthenticationFilter implements Filter { 
 
  @Autowired 
  SessionContext sessionContext; 
   
  private Logger log = LoggerFactory.getLogger(AuthenticationFilter.class);  
   
  @Override 
  public void init(FilterConfig filterConfig) throws ServletException { 
 
  } 
 
  @Override 
  public void doFilter(ServletRequest request, ServletResponse response, 
      FilterChain chain) throws IOException, ServletException { 
    HttpServletRequest req = (HttpServletRequest)request; 
    HttpServletResponse res = (HttpServletResponse) response; 
     
    //判断是否为ajax请求，默认不是 
    boolean isAjaxRequest = false; 
    if(!StrUtils.isBlank(req.getHeader("x-requested-with")) && req.getHeader("x-requested-with").equals("XMLHttpRequest")){ 
      isAjaxRequest = true; 
    } 
     
    SysUser sysUser = sessionContext.getSysUserFromSession(req); 
    if (sysUser != null && sysUser.getUserId() != null) { 
      chain.doFilter(req, res); 
    }else{//Session用户为空，登录过期 
      if(isAjaxRequest){// 如果是ajax请求，则不是跳转页面，使用response返回结果 
        res.setHeader("noAuthentication", "true"); 
        ResultWithObject resultWithObject = new ResultWithObject(CC.NEGATIVE_1, CC.RESULT_MESSAGE_TEXT_DEFAULT); 
        resultWithObject.setMsg("登录已失效，请刷新页面或重新登录！"); 
        res.setContentType("application/json;charset=UTF-8"); 
        PrintWriter writer = res.getWriter(); 
        writer.write(JasonUtils.Object2String(resultWithObject)); 
        writer.close(); 
        res.flushBuffer(); 
      }else{ 
        res.sendRedirect("http://xxxx.com/loginUI"); 
      } 
    } 
  } 
 
  @Override 
  public void destroy() { 
  } 
}