/*
* Copyright 2002-2010 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.web.filter;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServletResponseWrapper;
import org.springframework.util.DigestUtils;
import org.springframework.util.FileCopyUtils;
import org.springframework.web.util.WebUtils;
/**
* {@link javax.servlet.Filter} that generates an <code>ETag</code> value based on the content on the response.
* This ETag is compared to the <code>If-None-Match</code> header of the request. If these headers are equal,
* the response content is not sent, but rather a <code>304 "Not Modified"</code> status instead.
*
* <p>Since the ETag is based on the response content, the response (or {@link org.springframework.web.servlet.View})
* is still rendered. As such, this filter only saves bandwidth, not server performance.
*
* @author Arjen Poutsma
* @since 3.0
*/
public class ShallowEtagHeaderFilter extends OncePerRequestFilter {
private static String HEADER_ETAG = "ETag";
private static String HEADER_IF_NONE_MATCH = "If-None-Match";
@Override
protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
ShallowEtagResponseWrapper responseWrapper = new ShallowEtagResponseWrapper(response);
filterChain.doFilter(request, responseWrapper);
byte[] body = responseWrapper.toByteArray();
int statusCode = responseWrapper.getStatusCode();
if (isEligibleForEtag(request, responseWrapper, statusCode, body)) {
String responseETag = generateETagHeaderValue(body);
response.setHeader(HEADER_ETAG, responseETag);
String requestETag = request.getHeader(HEADER_IF_NONE_MATCH);
if (responseETag.equals(requestETag)) {
if (logger.isTraceEnabled()) {
logger.trace("ETag [" + responseETag + "] equal to If-None-Match, sending 304");
}
response.setContentLength(0);
response.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
}
else {
if (logger.isTraceEnabled()) {
logger.trace("ETag [" + responseETag + "] not equal to If-None-Match [" + requestETag +
"], sending normal response");
}
copyBodyToResponse(body, response);
}
}
else {
if (logger.isTraceEnabled()) {
logger.trace("Response with status code [" + statusCode + "] not eligible for ETag");
}
copyBodyToResponse(body, response);
}
}
private void copyBodyToResponse(byte[] body, HttpServletResponse response) throws IOException {
response.setContentLength(body.length);
if (body.length > 0) {
FileCopyUtils.copy(body, response.getOutputStream());
}
}
/**
* Indicates whether the given request and response are eligible for ETag generation.
* <p>The default implementation returns {@code true} for response status codes in the {@code 2xx} series.
* @param request the HTTP request
* @param response the HTTP response
* @param responseStatusCode the HTTP response status code
* @param responseBody the response body
* @return {@code true} if eligible for ETag generation; {@code false} otherwise
*/
protected boolean isEligibleForEtag(HttpServletRequest request, HttpServletResponse response,
int responseStatusCode, byte[] responseBody) {
return (responseStatusCode >= 200 && responseStatusCode < 300);
}
/**
* Generate the ETag header value from the given response body byte array.
* <p>The default implementation generates an MD5 hash.
* @param bytes the response bdoy as byte array
* @return the ETag header value
* @see org.springframework.util.DigestUtils
*/
protected String generateETagHeaderValue(byte[] bytes) {
StringBuilder builder = new StringBuilder("\"0");
DigestUtils.appendMd5DigestAsHex(bytes, builder);
builder.append('"');
return builder.toString();
}
/**
* {@link HttpServletRequest} wrapper that buffers all content written to the
* {@linkplain #getOutputStream() output stream} and {@linkplain #getWriter() writer},
* and allows this content to be retrieved via a {@link #toByteArray() byte array}.
*/
private static class ShallowEtagResponseWrapper extends HttpServletResponseWrapper {
private final ByteArrayOutputStream content = new ByteArrayOutputStream();
private final ServletOutputStream outputStream = new ResponseServletOutputStream();
private PrintWriter writer;
private int statusCode = HttpServletResponse.SC_OK;
private ShallowEtagResponseWrapper(HttpServletResponse response) {
super(response);
}
@Override
public void setStatus(int sc) {
super.setStatus(sc);
this.statusCode = sc;
}
@Override
public void setStatus(int sc, String sm) {
super.setStatus(sc, sm);
this.statusCode = sc;
}
@Override
public void sendError(int sc) throws IOException {
super.sendError(sc);
this.statusCode = sc;
}
@Override
public void sendError(int sc, String msg) throws IOException {
super.sendError(sc, msg);
this.statusCode = sc;
}
@Override
public ServletOutputStream getOutputStream() {
return this.outputStream;
}
@Override
public PrintWriter getWriter() throws IOException {
if (this.writer == null) {
String characterEncoding = getCharacterEncoding();
this.writer = (characterEncoding != null ? new ResponsePrintWriter(characterEncoding) :
new ResponsePrintWriter(WebUtils.DEFAULT_CHARACTER_ENCODING));
}
return this.writer;
}
@Override
public void resetBuffer() {
this.content.reset();
}
@Override
public void reset() {
super.reset();
resetBuffer();
}
private int getStatusCode() {
return statusCode;
}
private byte[] toByteArray() {
return this.content.toByteArray();
}
private class ResponseServletOutputStream extends ServletOutputStream {
@Override
public void write(int b) throws IOException {
content.write(b);
}
@Override
public void write(byte[] b, int off, int len) throws IOException {
content.write(b, off, len);
}
}
private class ResponsePrintWriter extends PrintWriter {
private ResponsePrintWriter(String characterEncoding) throws UnsupportedEncodingException {
super(new OutputStreamWriter(content, characterEncoding));
}
@Override
public void write(char buf[], int off, int len) {
super.write(buf, off, len);
super.flush();
}
@Override
public void write(String s, int off, int len) {
super.write(s, off, len);
super.flush();
}
@Override
public void write(int c) {
super.write(c);
super.flush();
}
}
}
}
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