如何在Spring MVC中代理HTTP请求？

Question

我有一个建立在Spring MVC之上的应用程序.

我想编写处理请求的简单代理,如下所示:

1. 将相同的HTTP请求发送到某个特定的服务器
2. 捕获来自此特定服务器的HTTP响应
3. 向请求客户端返回相同的答案

这是我到目前为止所得到的:

public void proxyRequest(HttpServletRequest request, HttpServletResponse response) {
    try {
        HttpUriRequest proxiedRequest = createHttpUriRequest(request);
        HttpResponse proxiedResponse = httpClient.execute(proxiedRequest);
        writeToResponse(proxiedResponse, response);
    } catch (URISyntaxException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

private void writeToResponse(HttpResponse proxiedResponse, HttpServletResponse response){
    for(Header header : proxiedResponse.getAllHeaders()){
        response.addHeader(header.getName(), header.getValue());
    }
    OutputStream os = null;
    InputStream is = null;
    try {
        is = proxiedResponse.getEntity().getContent();
        os = response.getOutputStream();
        IOUtils.copy(is, os);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        if (os != null) {
            try {
                os.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        if (is != null) {
            try {
                is.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

private HttpUriRequest createHttpUriRequest(HttpServletRequest request) throws URISyntaxException{
    URI uri = new URI(geoserverConfig.getUrl()+"/wms?"+request.getQueryString());

    RequestBuilder rb = RequestBuilder.create(request.getMethod());
    rb.setUri(uri);

    Enumeration<String> headerNames = request.getHeaderNames();
    while(headerNames.hasMoreElements()){
        String headerName = headerNames.nextElement();
        String headerValue = request.getHeader(headerName);
        rb.addHeader(headerName, headerValue);
    }

    HttpUriRequest proxiedRequest = rb.build();
    return proxiedRequest;
}

它工作正常但并非在所有情况下都可以.我已经检查了Chrome的网络监视器,并且使用此代理的一些请求失败了.

以下是示例失败请求响应的标头:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Disposition: inline; filename=JEDN_EWID.png
Transfer-Encoding: chunked
Date: Thu, 16 Jul 2015 10:31:49 GMT
Content-Type: image/png;charset=UTF-8
Content-Length: 6727

以下是示例成功请求响应的标头:

HTTP/1.1 200 OK
Server: Apache-Coyote/1.1
Content-Disposition: inline; filename=JEDN_EWID.png
Transfer-Encoding: chunked
Date: Thu, 16 Jul 2015 10:31:49 GMT
Content-Type: image/png;charset=UTF-8
Transfer-Encoding: chunked

更糟糕的是Chrome在控制台中抛出错误:

GET http://localhost:8080/<rest of url> net::ERR_INVALID_CHUNKED_ENCODING

我代理的请求是WMS GetMap请求,我的代理将它们转发给隐藏的Geoserver.我注意到失败的请求应该返回透明的512x512 .png图像,这些图像都是空的.成功的图像返回512x512 .png图像,这些图像不仅是透明的,还包含一些颜色.

Answer 1

当大小变得太大时,看起来远程服务器响应了分块响应,Apache HttpClient库在一个大的HttpResponse中收集所有分块的元素,但是留下了Transfer-Encoding: chunked标题.

我无法测试,但你应该过滤掉Transfer-Encoding: chunked以解决这个问题:

private void writeToResponse(HttpResponse proxiedResponse, HttpServletResponse response){
    for(Header header : proxiedResponse.getAllHeaders()){
        if ((! header.getName().equals("Transfer-Encoding")) || (! header.getValue().equals("chunked"))) {
            response.addHeader(header.getName(), header.getValue());
        }
    }
    ...