问题所在
在filter的doFilter(ServletRequest request, ServletResponse response, FilterChain chain)方法中我们可以取到request和response两个对象，形参中是接口，实际实现和web容器相关。在获取request中请求内容以及reponse中的响应内容时候，遇到如下两个问题：
-
request.getInputStream()的设计实现只能读一次（未实现reset方法），如果记录日志时候读取过，后续不能读取 -
response.getOutputStream()的具体实现依赖web容器，而且ServletOutputStream作为抽象类是被web容器继承来使用的，无法获取outputstream中的内容。
方案
为了解决上述问题，采取如下方案
针对问题1
针对request的inputstream不能重复读问题，继承HttpServletRequestWrapper，实现request请求内容的缓存。代码参考如下
public class LoggingHttpServletRequestWrapper extends HttpServletRequestWrapper {
private ByteArrayOutputStream cachedBytes;
public LoggingHttpServletRequestWrapper(HttpServletRequest request) {
super(request);
}
@Override
public ServletInputStream getInputStream() throws IOException {
if (cachedBytes == null) {
cacheInputStream(); //1. 将请求内容缓存到cachedBytes
}
return new CachedServletInputStream();//2. 当需要获取ServletInputStream时候，返回自定义实现的内部类
}
@Override
public BufferedReader getReader() throws IOException{
return new BufferedReader(new InputStreamReader(getInputStream()));
}
private void cacheInputStream() throws IOException {
/* Cache the inputstream in order to read it multiple times. For
* convenience, I use apache.commons IOUtils
*/
cachedBytes = new ByteArrayOutputStream();
IOUtils.copy(super.getInputStream(), cachedBytes);
}
/* An inputstream which reads the cached request body */
public class CachedServletInputStream extends ServletInputStream {
private ByteArrayInputStream input;
public CachedServletInputStream() {
/* create a new input stream from the cached request body */
input = new ByteArrayInputStream(cachedBytes.toByteArray());3. 使用缓存的请求内容初始化ByteArrayInputStream
}
@Override
public boolean isFinished() {
return false;
}
@Override
public boolean isReady() {
return false;
}
@Override
public void setReadListener(ReadListener readListener) {
}
@Override
public int read() throws IOException {
return input.read(); //4. 当外部调用ServletInputStream的read方法时候，使用初始化的input来返回
}
}
LoggingHttpServletRequestWrapper 自定义实现说明如下
- 将请求内容写到ByteArrayOutputStream cachedBytes来缓存
- 当需要获取ServletInputStream时候，返回自定义实现的内部类CachedServletInputStream
- CachedServletInputStream 使用缓存的cachedBytes内容初始化其私有字段ByteArrayInputStream input
- 当外部调用ServletInputStream的read方法时候，使用初始化的input来返回
如上所述就能实现request请求内容的多次读，使用代码如下
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
LoggingHttpServletRequestWrapper multiReadRequest = new LoggingHttpServletRequestWrapper((HttpServletRequest) request);
chain.doFilter(multiReadRequest,response);
}
针对问题2
同样，针对不能获取ServletOutputStream内容的问题，需要继承HttpServletResponseWrapper，代码参考如下
public class LoggingHttpServletResponseWrapper extends HttpServletResponseWrapper {
private final LoggingServletOutpuStream loggingServletOutpuStream = new LoggingServletOutpuStream(); //1. 也是实现了自定义的ServletOutputStream内部类LoggingServletOutpuStream，并初始化
private final HttpServletResponse delegate;
public LoggingHttpServletResponseWrapper(HttpServletResponse response) {
super(response);
delegate = response;
}
@Override
public ServletOutputStream getOutputStream() throws IOException {
return loggingServletOutpuStream; 2. 当外部获取ServletOutputStream时候返回内部实现类
}
@Override
public PrintWriter getWriter() throws IOException {
return new PrintWriter(loggingServletOutpuStream.baos);
}
public Map<String, String> getHeaders() {
Map<String, String> headers = new HashMap<>(0);
for (String headerName : getHeaderNames()) {
headers.put(headerName, getHeader(headerName));
}
return headers;
}
public String getContent() {
try {
String responseEncoding = delegate.getCharacterEncoding();
return loggingServletOutpuStream.baos.toString(responseEncoding != null ? responseEncoding : UTF_8.name());
} catch (UnsupportedEncodingException e) {
return "[UNSUPPORTED ENCODING]";
}
}
public byte[] getContentAsBytes() {
return loggingServletOutpuStream.baos.toByteArray(); 4. 获取请求内容时候从内部实现类的私有变量返回
}
private class LoggingServletOutpuStream extends ServletOutputStream {
private ByteArrayOutputStream baos = new ByteArrayOutputStream();
@Override
public boolean isReady() {
return true;
}
@Override
public void setWriteListener(WriteListener writeListener) {
}
@Override
public void write(int b) throws IOException {
baos.write(b);
}
@Override
public void write(byte[] b) throws IOException {
baos.write(b);
}
@Override
public void write(byte[] b, int off, int len) throws IOException {
baos.write(b, off, len); 3. 当向内部实现类LoggingServletOutpuStream 写入信息时，写到其内部字段baos上
}
}
LoggingHttpServletResponseWrapper 自定义实现说明如下
- 也是实现了自定义的ServletOutputStream内部类LoggingServletOutpuStream，并初始化
- 当外部获取ServletOutputStream时候返回内部实现类
- 当向内部实现类LoggingServletOutpuStream 写入信息时，写到其内部字段baos上
- 获取请求内容时候从内部实现类的私有变量返回
如上所述就能实现获取response的内容，使用代码如下
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
LoggingHttpServletRequestWrapper multiReadRequest = new LoggingHttpServletRequestWrapper((HttpServletRequest) request);
LoggingHttpServletResponseWrapper responseWrapper = new LoggingHttpServletResponseWrapper((HttpServletResponse) response);
chain.doFilter(multiReadRequest,contentWrapper );
response.getOutputStream().write(contentWrapper.getContentAsByteArray());//最后注意需要请reponsewrapper的内容写入到原始response
String s = contentWrapper.getContent();//就能获取到内容
}
其实对于ResponseWrapper有现成的实现，就是ContentCachingResponseWrapper，因此上述代码可以变更如下
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) {
ContentCachingResponseWrappermultiReadRequest = new ContentCachingResponseWrapper((HttpServletRequest) request);
LoggingHttpServletResponseWrapper responseWrapper = new LoggingHttpServletResponseWrapper((HttpServletResponse) response);
chain.doFilter(multiReadRequest,contentWrapper );
byte[] s = contentWrapper .getContentAsByteArray();//就能获取到内容
contentWrapper.copyBodyToResponse();//最后注意需要请reponsewrapper的内容写入到原始response, 最后一步执行，因为执行完后ContentCachingResponseWrapper的FastByteArrayOutputStream会被重置
}
拿到请求内容和响应内容后，就可以自由记录日志了，在此不在赘述。
