请求的资源上不存在"访问控制允许源"标头。

Question

我正在使用SpringMVC。我想用web服务调用XML文件，以便稍后解析它。问题是我无法访问XML文件，我得到了这个错误:请求的资源上没有"access - control - allow - origin"标头。我尝试了下面的解决方案:

我创建了一个新类，目的是在请求的资源上添加Access-Control-Allow-Origin'标头。这是类

package com.mycompany.myapp;
import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class JsonpFilter implements Filter {
private String functionName;
@Override
public void destroy() {
}
@Override
public void doFilter(ServletRequest request, ServletResponse servletResponse,
                     FilterChain chain) throws IOException, ServletException {
    if (!(request instanceof HttpServletRequest)) {
        throw new ServletException("This filter can "
                                   + " only process HttpServletRequest requests");
    }
    HttpServletRequest httpRequest = (HttpServletRequest) request;
    HttpServletResponse response = (HttpServletResponse) servletResponse;
    if (isJSONPRequest(httpRequest)) {
        ServletOutputStream out = response.getOutputStream();
        out.println(getCallbackMethod(httpRequest) + "(");
        chain.doFilter(request, response);
        out.println(");");
        response.setContentType("text/javascript");
    } else {
        response.addHeader("Access-Control-Allow-Origin", "*");
        chain.doFilter(request, response);
    }
}
@Override
public void init(FilterConfig filterConfig) throws ServletException {
    this.functionName = filterConfig.getInitParameter("encoding");
    if(this.functionName == null || this.functionName.length() <= 0) {
        this.functionName = "callback";
    }
}
private String getCallbackMethod(HttpServletRequest httpRequest) {
    return httpRequest.getParameter(this.functionName);
}
private boolean isJSONPRequest(HttpServletRequest httpRequest) {
    String callbackMethod = getCallbackMethod(httpRequest);
    return (callbackMethod != null && callbackMethod.length() > 0);
}

}

然后我在我的web.xml文件中添加这两行:

    <display-name>DataServices</display-name>
   <filter>
    <filter-name>JSONPRequestFilter</filter-name>
    <filter-class> com.mycompany.myapp.JsonpFilter</filter-class>
    <init-param>
        <param-name>functionName</param-name>
        <param-value>callback</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>JSONPRequestFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

我没有任何编译问题，但在执行时控制台中仍然有相同的错误。所以，'Access-Control-Allow-Origin'报头没有被考虑。如果你能找出我的程序有什么问题，或者给我另一个解决方案，我将不胜感激

Answer 1

实现这个接口

org.springframework.web.servlet.HandlerInterceptor

这里有一个例子

@Component
public class CORSInterceptor implements HandlerInterceptor{
   private static final Log LOG = LogFactory.getLog(CORSInterceptor.class);
   @Override
   public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
       LOG.trace("sending headers");
       response.setHeader("Access-Control-Allow-Origin", "*");
       response.setHeader("Access-Control-Allow-Methods", "POST, GET, PUT, DELETE");
       response.setHeader("Access-Control-Max-Age", "3600");
       response.setHeader("Access-Control-Allow-Headers", "x-requested-with");
       return true;
   }
   @Override
   public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
        throws Exception {
   }
   @Override
   public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
        throws Exception {
        LOG.trace("afterCompletion is called");
   }
}

然后将这一行添加到应用程序上下文

<mvc:interceptors>
    <bean class="com.elm.mb.rest.interceptors.CORSInterceptor" />
</mvc:interceptors>