寻找 HttpServletResponseWrapper 的捕获实现

JavaEE API 附带了 HttpServletResponseWrapper，引用 javadoc 的话，“提供了 HttpServletResponse 接口的便捷实现，希望适应 Servlet 响应的开发人员可以对其进行子类化。”如果没有子类化，此类只是将所有调用传递给包装的响应对象。有一个类似的请求包装器。

任何人都可以向我指出任何提供这些类的有用子类实现的实用程序库吗？特别是，我正在寻找响应包装器的子类，它捕获写入的响应（作为 String、byte[] 或任何合适的形式）并通过 API 方法公开它。

我自己写了一个相当不成熟的版本，但坦率地说，我不应该这样做，我宁愿扔掉它并使用现成的版本。

我不知道有任何实现，尽管只需写入 ByteArrayOutputStream 即可轻松调整 gzip 示例。您还可以通过查看其他响应包装器实现来获取想法：

• SiteMesh http://www.sitemesh.org/
• DWR http://directwebremoting.org/也用它

原答案：

JavaWorld里有一篇经典文章使用Servlet 2.3模型过滤代码 http://www.javaworld.com/javaworld/jw-06-2001/jw-0622-filters.html。您可以找到包装请求和响应的示例：

• 压缩响应 http://www.javaworld.com/javaworld/jw-06-2001/jw-0622-filters.html?page=4

  public class CompressionResponseWrapper extends HttpServletResponseWrapper {
    protected ServletOutputStream stream = null;
    protected PrintWriter writer = null;
    protected int threshold = 0;
    protected HttpServletResponse origResponse = null;
    public CompressionResponseWrapper(HttpServletResponse response) {
  super(response);
  origResponse = response;
    }
    public void setCompressionThreshold(int threshold) {
  this.threshold = threshold;
    }
    public ServletOutputStream createOutputStream() throws IOException {
  return (new CompressionResponseStream(origResponse));
    }
    public ServletOutputStream getOutputStream() throws IOException {
  if (writer != null) {
    throw new IllegalStateException("getWriter() has already been " +
                                    "called for this response");
  }
  if (stream == null) {
    stream = createOutputStream();
  }
  ((CompressionResponseStream) stream).setCommit(true);
  ((CompressionResponseStream) stream).setBuffer(threshold);
  return stream;
    }
    public PrintWriter getWriter() throws IOException {
  if (writer != null) {
    return writer;
  }
  if (stream != null) {
    throw new IllegalStateException("getOutputStream() has already " +
                                    "been called for this response");
  }
  stream = createOutputStream();
  ((CompressionResponseStream) stream).setCommit(true);
  ((CompressionResponseStream) stream).setBuffer(threshold);
  writer = new PrintWriter(stream);
  return writer;
    }
  }
  

• 处理文件上传 http://www.javaworld.com/javaworld/jw-06-2001/jw-0622-filters.html?page=5

  public class MultipartWrapper extends HttpServletRequestWrapper {
    MultipartRequest mreq = null;
    public MultipartWrapper(HttpServletRequest req, String dir)
                                   throws IOException {
  super(req);
  mreq = new MultipartRequest(req, dir);
    }
    // Methods to replace HSR methods
    public Enumeration getParameterNames() {
  return mreq.getParameterNames();
    }
    public String getParameter(String name) {
  return mreq.getParameter(name);
    }
    public String[] getParameterValues(String name) {
  return mreq.getParameterValues(name);
    }
    public Map getParameterMap() {
  Map map = new HashMap();
  Enumeration enum = getParameterNames();
  while (enum.hasMoreElements()) {
    String name = (String) enum.nextElement();
    map.put(name, mreq.getParameterValues(name));
  }
  return map;
    }
    // Methods only in MultipartRequest
    public Enumeration getFileNames() {
  return mreq.getFileNames();
    }
    public String getFilesystemName(String name) {
  return mreq.getFilesystemName(name);
    }
    public String getContentType(String name) {
  return mreq.getContentType(name);
    }
    public File getFile(String name) {
  return mreq.getFile(name);
    }
  }
  

该代码有点旧（2001 年 6 月！），但它很好地演示了用法。