Java过滤器 - 根据请求有条件地更改响应正文

Question

我有一个 servlet 过滤器，它拦截请求并检查自定义“加密”标头：

public class EncryptionFilter extends GenericFilterBean{

@Override
public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain filterChain) {
    final HttpServletRequest httpRequest = (HttpServletRequest) request;
    if (httpRequest.getHeader("EncryptedCommunication") != null){
        decryptedRequest = /*decrypt request body and forward to next filter*/
        encryptedResponse = /*encrypt request body and forward to next filter*/
        filterChain.doFilter(decryptedRequest, encryptedResponse);
    }
    else { /* communication not encrypted */
        filterChain.doFilter(request, response);
    }
  }
}

当标头存在时，我应该解密请求正文并加密响应正文。 否则，应保持请求/响应正文不变。

如何仅在需要时更改响应？

Answer 1

你需要使用一个HttpServletResponseWrapper的例子是：

filterChain.doFilter(servletRequest,
        new HttpServletResponseWrapper((HttpServletResponse) servletResponse) {
            @Override
            public void setHeader(String name, String value) {
                if (!HTTPCacheHeader.ETAG.getName().equalsIgnoreCase(name)) {
                    super.setHeader(name, value);
                }
            }
        });

见http://www.programcreek.com/java-api-examples/javax.servlet.http.HttpServletResponseWrapper

这是如何设置主体的示例：

public class ReadTwiceHttpServletRequestWrapper extends HttpServletRequestWrapper {

private ByteArrayOutputStream outputStream = new ByteArrayOutputStream();

public ReadTwiceHttpServletRequestWrapper(HttpServletRequest request) {
    super(request);
    try {
        IOUtils.copy(request.getInputStream(), outputStream);
    } catch (IOException e) {
        e.printStackTrace();
    }
}

@Override
public BufferedReader getReader() throws IOException {
    return new BufferedReader(new InputStreamReader(new ByteArrayInputStream(outputStream.toByteArray())));
}

@Override
public ServletInputStream getInputStream() throws IOException {
    final ByteArrayInputStream inputStream = new ByteArrayInputStream(outputStream.toByteArray());
    return new ServletInputStream() {

        @Override
        public int readLine(byte[] b, int off, int len) throws IOException {
            return inputStream.read(b, off, len);
        }

        @Override
        public boolean isFinished() {
            return inputStream.available() > 0;
        }

        @Override
        public boolean isReady() {
            return true;
        }

        @Override
        public void setReadListener(ReadListener arg0) {
            // TODO Auto-generated method stub
        }

        @Override
        public int read() throws IOException {
            return inputStream.read();
        }
    };
}

public void setBody(String body) {
    outputStream = new ByteArrayOutputStream();
    try {
        outputStream.write(body.getBytes());
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

public String getBody() {
    return new String(outputStream.toByteArray());
}

见How to get the XML from POST request and modify it in Servlet Filter?