[转]在filter中打印HttpSevletResponse的body

源地址stackoverflow
基本思想：使用HttpServletResponseWrapper复制body内容

Filter代码

@WebFilter("/*")
public class ResponseLogger implements Filter {

@Override
public void init(FilterConfig config) throws ServletException {
// NOOP.
}

@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws ServletException, IOException {
if (response.getCharacterEncoding() == null) {
response.setCharacterEncoding("UTF-8"); // Or whatever default. UTF-8 is good for World Domination.
}

HttpServletResponseCopier responseCopier = new HttpServletResponseCopier((HttpServletResponse) response);

try {
chain.doFilter(request, responseCopier);
responseCopier.flushBuffer();
} finally {
byte[] copy = responseCopier.getCopy();
System.out.println(new String(copy, response.getCharacterEncoding())); // Do your logging job here. This is just a basic example.
}
}

@Override
public void destroy() {
// NOOP.
}

}

HttpServletResponseWrapper代码

public class HttpServletResponseCopier extends HttpServletResponseWrapper {

private ServletOutputStream outputStream;
private PrintWriter writer;
private ServletOutputStreamCopier copier;

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

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

if (outputStream == null) {
outputStream = getResponse().getOutputStream();
copier = new ServletOutputStreamCopier(outputStream);
}

return copier;
}

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

if (writer == null) {
copier = new ServletOutputStreamCopier(getResponse().getOutputStream());
writer = new PrintWriter(new OutputStreamWriter(copier, getResponse().getCharacterEncoding()), true);
}

return writer;
}

@Override
public void flushBuffer() throws IOException {
if (writer != null) {
writer.flush();
} else if (outputStream != null) {
copier.flush();
}
}

public byte[] getCopy() {
if (copier != null) {
return copier.getCopy();
} else {
return new byte[0];
}
}

}

ServletOutputStream代码

public class ServletOutputStreamCopier extends ServletOutputStream {

private OutputStream outputStream;
private ByteArrayOutputStream copy;

public ServletOutputStreamCopier(OutputStream outputStream) {
this.outputStream = outputStream;
this.copy = new ByteArrayOutputStream(1024);
}

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

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

}