利用HttpServletResponseWrapper修改Response對象

使用servlet從HttpServletResponse讀取輸出流，並對輸出流做一些修改，但是如果我們直接對原始response進行操作則會造成輸出流提前打開或者關閉，導致不能從一次請求中完成對輸出流的修改。

所以我們可以通過繼承HttpServletResponseWrapper對象來獲取原始的輸出流，通過PrintWriter將輸出流寫入到Buffer中。

public class ResponseWrapper extends HttpServletResponseWrapper {
    private PrintWriter cachedWriter;
    private CharArrayWriter bufferedWriter;

    /**
     * Constructs a response adaptor wrapping the given response.
     *
     * @param response The response to be wrapped
     * @throws IllegalArgumentException if the response is null
     */
    public ResponseWrapper(HttpServletResponse response) {
        super(response);
        bufferedWriter = new CharArrayWriter();
        cachedWriter = new PrintWriter(bufferedWriter);
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        return cachedWriter;
    }

    /**
     * 獲取原始HTML
     *
     * @return
     */
    public String getResult() {
        byte[] bytes = bufferedWriter.toString().getBytes();
        try {
            return new String(bytes, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            return "";
        }
    }
}

通過過濾器攔截Response對象，然后就可以對輸出流進行操作了。

public class ResponseFilter implements Filter {
    @Override
    public void init(javax.servlet.FilterConfig filterConfig) throws ServletException {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        ResponseWrapper wrapper = new ResponseWrapper((HttpServletResponse) response);
        chain.doFilter(request, wrapper);
        String result = wrapper.getResult();
        response.getOutputStream().write(result.getBytes());
    }

    @Override
    public void destroy() {

    }
}