通过HttpServletResponseWrapper获取到返回body

1.日志追踪系统需要获取到接口返回body，因此需要重写getWritter()避免getOutputStream() has been call的异常。

public class HttpServletResponseCopier extends HttpServletResponseWrapper {
    private int statusCode;
    private ServletOutputStreamCopier streamCopier;
    private PrintWriterCopier         writerCopier;
    private boolean                   useWriter;

    public HttpServletResponseCopier(HttpServletResponse response) throws IOException {
        super(response);
        useWriter = true;
    }

    @Override
    public ServletOutputStream getOutputStream() throws IOException {
        if (writerCopier != null) {
            throw new IllegalStateException("getWriter() has already been called on this response.");
        }

        if (streamCopier == null) {
            useWriter = false;
            streamCopier = new ServletOutputStreamCopier();
        }

        return streamCopier;
    }

    @Override
    public PrintWriter getWriter() throws IOException {
        if (streamCopier != null) {
            throw new IllegalStateException("getOutputStream() has already been called on this response.");
        }

        if (writerCopier == null) {
            useWriter = true;
            writerCopier = new PrintWriterCopier();
        }

        return writerCopier.getWriter();
    }

    public byte[] getBytes() {
        if (streamCopier==null && writerCopier==null) {
            return new byte[0];
        }

        return useWriter ? writerCopier.getBytes() : streamCopier.getCopy();
    }

    public byte[] getStreamCopy() {
        if (useWriter) {
            throw new IllegalStateException("already use writer, please call getWriterCopy()");
        }

        return streamCopier==null ? new byte[0] : streamCopier.getCopy();
    }

    public char[] getWriterCopy() {
        if (!useWriter) {
            throw new IllegalStateException("already use outputStream, please call getStreamCopy()");
        }

        return writerCopier==null ? new char[0] : writerCopier.getCopy();
    }

    /**
     * The default behavior of this method is to call sendError(int sc, String msg)
     * on the wrapped response object.
     */
    public void sendError(int sc, String msg) throws IOException {
        ((HttpServletResponse)getResponse()).sendError(sc, msg);
        this.statusCode = sc;
    }

    /**
     * The default behavior of this method is to call sendError(int sc)
     * on the wrapped response object.
     */
    public void sendError(int sc) throws IOException {
        ((HttpServletResponse)getResponse()).sendError(sc);
        this.statusCode = sc;
    }

    public void setStatus(int sc) {
        super.setStatus(sc);
        this.statusCode = sc;
    }

    /**
     * The default behavior of this method is to call setStatus(int sc, String sm)
     * on the wrapped response object.
     */
    public void setStatus(int sc, String sm) {
        super.setStatus(sc, sm);
        this.statusCode = sc;
    }

    public int getStatus() {
        return statusCode;
    }

    public boolean isUseWriter() {
        return useWriter;
    }
}

public class PrintWriterCopier {
    private CharArrayWriter charArrayWriter;
    private PrintWriter writer;

    public PrintWriterCopier() {
        this.charArrayWriter = new CharArrayWriter();
        this.writer = new PrintWriter(charArrayWriter);
    }

    public PrintWriter getWriter() {
        return writer;
    }

    public char[] getCopy() {
        return charArrayWriter.toCharArray();
    }

    public byte[] getBytes() {
        return charArrayWriter.toString().getBytes();
    }
}

/**
 * 拷贝Servlet输出
 *
 * Created by hai on 16/12/13.
 */
public class ServletOutputStreamCopier extends ServletOutputStream {
    private static final int INIT_BUFFER_SIZE = 1024;

    private ByteArrayOutputStream copy;

    public ServletOutputStreamCopier() {
        this.copy = new ByteArrayOutputStream(INIT_BUFFER_SIZE);
    }

    @Override
    public void write(int b) throws IOException {
        copy.write(b);
    }

    public byte[] getCopy() {
        return copy.toByteArray();
    }

    @Override
    public void flush() throws IOException {
        copy.flush();
    }
}

filter:

 @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain) throws IOException, ServletException {
    HttpServletResponseCopier responseCopier = new HttpServletResponseCopier(response);
        try {
            chain.doFilter(request, responseCopier);
        } catch (Exception e) {
            e.printStackTrack();
        }
        //写入结果
        writeResponse(responseCopier, response);

}


private void writeResponse(HttpServletResponseCopier copier, HttpServletResponse response) throws IOException {
 if (copier.isUseWriter()) {
        PrintWriter out = response.getWriter();
        out.write(copier.getWriterCopy());
        out.flush();
        out.close();
    } else {
        OutputStream out = response.getOutputStream();
        out.write(copier.getStreamCopy());
        out.flush();
        out.close();
    }
}