Spring cloud zull 的SendResponseFilter主要工作是将代理请求获取的reponse写入当前response，发送回客户端。以下是源代码：
public class SendResponseFilter extends ZuulFilter {
private static final Log log = LogFactory.getLog(SendResponseFilter.class);
private static DynamicBooleanProperty INCLUDE_DEBUG_HEADER = DynamicPropertyFactory
.getInstance()
.getBooleanProperty(ZuulConstants.ZUUL_INCLUDE_DEBUG_HEADER, false);
private static DynamicIntProperty INITIAL_STREAM_BUFFER_SIZE = DynamicPropertyFactory
.getInstance()
.getIntProperty(ZuulConstants.ZUUL_INITIAL_STREAM_BUFFER_SIZE, 8192);
private static DynamicBooleanProperty SET_CONTENT_LENGTH = DynamicPropertyFactory
.getInstance()
.getBooleanProperty(ZuulConstants.ZUUL_SET_CONTENT_LENGTH, false);
private boolean useServlet31 = true;
public SendResponseFilter() {
super();
// To support Servlet API 3.0.1 we need to check if setcontentLengthLong exists
try {
HttpServletResponse.class.getMethod("setContentLengthLong");
} catch(NoSuchMethodException e) {
useServlet31 = false;
}
}
private ThreadLocal buffers = new ThreadLocal() {
@Override
protected byte[] initialValue() {
return new byte[INITIAL_STREAM_BUFFER_SIZE.get()];
}
};
@Override
public String filterType() {
return POST_TYPE;
}
@Override
public int filterOrder() {
return SEND_RESPONSE_FILTER_ORDER;
}
@Override
public boolean shouldFilter() {
RequestContext context = RequestContext.getCurrentContext();
return context.getThrowable() == null
&& (!context.getZuulResponseHeaders().isEmpty()
|| context.getResponseDataStream() != null
|| context.getResponseBody() != null);
}
@Override
public Object run() {
try {
addResponseHeaders();
writeResponse();
}
catch (Exception ex) {
ReflectionUtils.rethrowRuntimeException(ex);
}
return null;
}
private void writeResponse() throws Exception {
RequestContext context = RequestContext.getCurrentContext();
// there is no body to send
if (context.getResponseBody() == null
&& context.getResponseDataStream() == null) {
return;
}
HttpServletResponse servletResponse = context.getResponse();
if (servletResponse.getCharacterEncoding() == null) { // only set if not set
servletResponse.setCharacterEncoding("UTF-8");
}
OutputStream outStream = servletResponse.getOutputStream();
InputStream is = null;
try {
if (RequestContext.getCurrentContext().getResponseBody() != null) {
String body = RequestContext.getCurrentContext().getResponseBody();
writeResponse(
new ByteArrayInputStream(
body.getBytes(servletResponse.getCharacterEncoding())),
outStream);
return;
}
boolean isGzipRequested = false;
final String requestEncoding = context.getRequest()
.getHeader(ZuulHeaders.ACCEPT_ENCODING);
if (requestEncoding != null
&& HTTPRequestUtils.getInstance().isGzipped(requestEncoding)) {
isGzipRequested = true;
}
is = context.getResponseDataStream();
InputStream inputStream = is;
if (is != null) {
if (context.sendZuulResponse()) {
// if origin response is gzipped, and client has not requested gzip,
// decompress stream
// before sending to client
// else, stream gzip directly to client
if (context.getResponseGZipped() && !isGzipRequested) {
// If origin tell it's GZipped but the content is ZERO bytes,
// don't try to uncompress
final Long len = context.getOriginContentLength();
if (len == null || len > 0) {
try {
inputStream = new GZIPInputStream(is);
}
catch (java.util.zip.ZipException ex) {
log.debug(
"gzip expected but not "
+ "received assuming unencoded response "
+ RequestContext.getCurrentContext()
.getRequest().getRequestURL()
.toString());
inputStream = is;
}
}
else {
// Already done : inputStream = is;
}
}
else if (context.getResponseGZipped() && isGzipRequested) {
servletResponse.setHeader(ZuulHeaders.CONTENT_ENCODING, "gzip");
}
writeResponse(inputStream, outStream);
}
}
}
finally {
/**
* Closing the wrapping InputStream itself has no effect on closing the underlying tcp connection since it's a wrapped stream. I guess for http
* keep-alive. When closing the wrapping stream it tries to reach the end of the current request, which is impossible for infinite http streams. So
* instead of closing the InputStream we close the HTTP response.
*
* @author Johannes Edmeier
*/
try {
Object zuulResponse = RequestContext.getCurrentContext()
.get("zuulResponse");
if (zuulResponse instanceof Closeable) {
((Closeable) zuulResponse).close();
}
outStream.flush();
// The container will close the stream for us
}
catch (IOException ex) {
log.warn("Error while sending response to client: " + ex.getMessage());
}
}
}
private void writeResponse(InputStream zin, OutputStream out) throws Exception {
byte[] bytes = buffers.get();
int bytesRead = -1;
while ((bytesRead = zin.read(bytes)) != -1) {
out.write(bytes, 0, bytesRead);
}
}
private void addResponseHeaders() {
RequestContext context = RequestContext.getCurrentContext();
HttpServletResponse servletResponse = context.getResponse();
if (INCLUDE_DEBUG_HEADER.get()) {
@SuppressWarnings("unchecked")
List rd = (List) context.get(ROUTING_DEBUG_KEY);
if (rd != null) {
StringBuilder debugHeader = new StringBuilder();
for (String it : rd) {
debugHeader.append("[[[" + it + "]]]");
}
servletResponse.addHeader(X_ZUUL_DEBUG_HEADER, debugHeader.toString());
}
}
List> zuulResponseHeaders = context.getZuulResponseHeaders();
if (zuulResponseHeaders != null) {
for (Pair it : zuulResponseHeaders) {
servletResponse.addHeader(it.first(), it.second());
}
}
// Only inserts Content-Length if origin provides it and origin response is not
// gzipped
if (SET_CONTENT_LENGTH.get()) {
Long contentLength = context.getOriginContentLength();
if ( contentLength != null && !context.getResponseGZipped()) {
if(useServlet31) {
servletResponse.setContentLengthLong(contentLength);
} else {
//Try and set some kind of content length if we can safely convert the Long to an int
if (isLongSafe(contentLength)) {
servletResponse.setContentLength(contentLength.intValue());
}
}
}
}
}
private boolean isLongSafe(long value) {
return value <= Integer.MAX_VALUE && value >= Integer.MIN_VALUE;
}
}
filterType：
post
filterOrder：
1000，是post阶段最后执行的过滤器
shouldFilter：
public boolean shouldFilter() {
RequestContext context = RequestContext.getCurrentContext();
return context.getThrowable() == null
&& (!context.getZuulResponseHeaders().isEmpty()
|| context.getResponseDataStream() != null
|| context.getResponseBody() != null);
}
该过滤器会检查请求上下文中是否包含请求响应相关的头信息(zuulResponseHeaders)、响应数据流(responseDataStream)或是响应体(responseBody)，只有在包含它们其中一个且没有异常抛出的时候才会执行处理逻辑。
run:
主要做了两件事
1、添加响应头
addResponseHeaders();
private void addResponseHeaders() {
RequestContext context = RequestContext.getCurrentContext();
HttpServletResponse servletResponse = context.getResponse();
if (INCLUDE_DEBUG_HEADER.get()) {
@SuppressWarnings("unchecked")
List rd = (List) context.get(ROUTING_DEBUG_KEY);
if (rd != null) {
StringBuilder debugHeader = new StringBuilder();
for (String it : rd) {
debugHeader.append("[[[" + it + "]]]");
}
servletResponse.addHeader(X_ZUUL_DEBUG_HEADER, debugHeader.toString());
}
}
List> zuulResponseHeaders = context.getZuulResponseHeaders();
if (zuulResponseHeaders != null) {
for (Pair it : zuulResponseHeaders) {
servletResponse.addHeader(it.first(), it.second());
}
}
// Only inserts Content-Length if origin provides it and origin response is not
// gzipped
if (SET_CONTENT_LENGTH.get()) {
Long contentLength = context.getOriginContentLength();
if ( contentLength != null && !context.getResponseGZipped()) {
if(useServlet31) {
servletResponse.setContentLengthLong(contentLength);
} else {
//Try and set some kind of content length if we can safely convert the Long to an int
if (isLongSafe(contentLength)) {
servletResponse.setContentLength(contentLength.intValue());
}
}
}
}
}
ZUUL_INCLUDE_DEBUG_HEADER主要涉及到zuul.include-debug-header的配置，如果为true，且请求中带有debug=true或zuul.debug.request
配置为true，则 debug信息将会添加到X-Zuul-Debug-Header响应header中，你可以将它作为信息返回给网关调用方，也可以通过调用com.netflix.zuul.context.Debug.getRoutingDebug().自己打印出来，方法可参考：
https://stackoverflow.com/questions/43910195/where-can-i-find-the-debug-information-in-zuul
接着是把zuulResponseHeaders放入到当前response中，那zuulResponseHeaders原先是怎么放到context中的呢，以我们使用SimpleHostRoutingFilter为例子：
其内部执行：
CloseableHttpResponse response = forward(this.httpClient, verb, uri, request,
headers, params, requestEntity);
setResponse(response);
sendResponse:
private void setResponse(HttpResponse response) throws IOException {
RequestContext.getCurrentContext().set("zuulResponse", response);
this.helper.setResponse(response.getStatusLine().getStatusCode(),
response.getEntity() == null ? null : response.getEntity().getContent(),
revertHeaders(response.getAllHeaders()));
}
this.helper.setResponse:
public void setResponse(int status, InputStream entity,
MultiValueMap headers) throws IOException {
RequestContext context = RequestContext.getCurrentContext();
context.setResponseStatusCode(status);
if (entity != null) {
context.setResponseDataStream(entity);
}
HttpHeaders httpHeaders = new HttpHeaders();
for (Entry> header : headers.entrySet()) {
List values = header.getValue();
for (String value : values) {
httpHeaders.add(header.getKey(), value);
}
}
boolean isOriginResponseGzipped = false;
if (httpHeaders.containsKey(CONTENT_ENCODING)) {
List collection = httpHeaders.get(CONTENT_ENCODING);
for (String header : collection) {
if (HTTPRequestUtils.getInstance().isGzipped(header)) {
isOriginResponseGzipped = true;
break;
}
}
}
context.setResponseGZipped(isOriginResponseGzipped);
for (Entry> header : headers.entrySet()) {
String name = header.getKey();
for (String value : header.getValue()) {
context.addOriginResponseHeader(name, value);
if (name.equalsIgnoreCase(CONTENT_LENGTH)) {
context.setOriginContentLength(value);
}
if (isIncludedHeader(name)) {
context.addZuulResponseHeader(name, value);
}
}
}
}
如上述代码所示，根据转发时获取的origin response，将相关信息设置到context中，以备后续使用，这些信息包括：responseStatusCode(响应状态码)、responseDataStream(响应输入流)、responseGZipped(原始响应是否Gzipped)、originResponseHeaders(原始响应头)、originContentLength(原始响应实体长度)、zuulResponseHeaders(从originResponseHeaders中过滤了部分header信息，具体看下面isIncludedHeader方法)
public boolean isIncludedHeader(String headerName) {
String name = headerName.toLowerCase();
RequestContext ctx = RequestContext.getCurrentContext();
if (ctx.containsKey(IGNORED_HEADERS)) {
Object object = ctx.get(IGNORED_HEADERS);
if (object instanceof Collection && ((Collection) object).contains(name)) {
return false;
}
}
switch (name) {
case "host":
case "connection":
case "content-length":
case "content-encoding":
case "server":
case "transfer-encoding":
case "x-application-context":
return false;
default:
return true;
}
}
为什么要过滤这些以上这些字段呢，因为这些都是目标主机特定于代理网关的http头，而不是代理网关特定于客户端的http头，像host，serve、connection、content-encoding等，代理网关可能根据客户端请求信息，当前网络状态设置不一样的值。有些像content-length，后面作了特别处理。
最后是设置当前响应的content-length，SET_CONTENT_LENGTH对应的配置项是zuul.set-content-length，如果是true，并且目标主机提供Content-Length而且响应没有被gzipped压缩时，才插入Content-Length。为什么gzipped压缩时不传入呢，通过后面的run方法内容可知，如果原始response是经过gzip压缩，而网关client没有要求gzip压缩，则在发送给客户端之前先解压响应流，因此此时一旦设置了Content-Length， 便会导致实际的传输长度比Content-Length要长的情况，导致截断。
// if origin response is gzipped, and client has not requested gzip,
// decompress stream
// before sending to client
// else, stream gzip directly to client
if (context.getResponseGZipped() && !isGzipRequested) {
// If origin tell it's GZipped but the content is ZERO bytes,
// don't try to uncompress
final Long len = context.getOriginContentLength();
if (len == null || len > 0) {
try {
inputStream = new GZIPInputStream(is);
}
catch (java.util.zip.ZipException ex) {
log.debug(
"gzip expected but not "
+ "received assuming unencoded response "
+ RequestContext.getCurrentContext()
.getRequest().getRequestURL()
.toString());
inputStream = is;
}
}
else {
// Already done : inputStream = is;
}
}
else if (context.getResponseGZipped() && isGzipRequested) {
servletResponse.setHeader(ZuulHeaders.CONTENT_ENCODING, "gzip");
}
可能有些童鞋不大清楚content-length的作用，在此作一个普及：
Content-Length指示出报文中的实体主体的字节大小，它主要为了检测出服务器崩溃导致的报文截尾，并对持久连接的多个报文进行正确分段。 如果主体进行了内容编码，它指示编码后的主体的字节长度。如果不是持久连接，那么不需要知道它正在读取的主体的长度，只需要读到服务器关闭主体连接为止，如果是持久连接，在服务器写主体前，必须知道它的大小并在Content-length中发送，若服务器动态创建内容，则发送前无法知道主体的长度，那怎么办呢？这时可以用transfer-encoding替代，在头部加入 Transfer-Encoding: chunked 之后，就代表这个报文采用了分块编码。这时，报文中的实体需要改为用一系列分块来传输。每个分块包含十六进制的长度值和数据，长度值独占一行，长度不包括它结尾的 CRLF（\r\n），也不包括分块数据结尾的 CRLF。最后一个分块长度值必须为 0，对应的分块数据没有内容，表示实体结束。(详细可参考https://imququ.com/post/transfer-encoding-header-in-http.html)
那假如SET_CONTENT_LENGTH为false，既然SendResponseFilter中没看到设置Content-Length的代码，也没设置 transfer-encoding，那么是在哪里作处理的呢，调试代码可知，是在tomcat中处理的：
zuul 内部可以不对content length或Tansfer-Encoding进行设置，由org.apache.catalina.connector.ResponseFacade进行
调试代码，查看org.apache.catalina.connector.CoyoteOutputStream. close源码
@Override
public void close() throws IOException {
ob.close();
}
ob即outputbuffer，close时内部将执行doFlush：
protected void doFlush(boolean realFlush) throws IOException {
if (suspended) {
return;
}
try {
doFlush = true;
if (initial) {
coyoteResponse.sendHeaders();
initial = false;
}
if (cb.remaining() > 0) {
flushCharBuffer();
}
if (bb.remaining() > 0) {
flushByteBuffer();
}
} finally {
doFlush = false;
}
if (realFlush) {
coyoteResponse.action(ActionCode.CLIENT_FLUSH, null);
// If some exception occurred earlier, or if some IOE occurred
// here, notify the servlet with an IOE
if (coyoteResponse.isExceptionPresent()) {
throw new ClientAbortException(coyoteResponse.getErrorException());
}
}
}
Http11Processor的prepareResponse方法：
如果存在contentLength，则设置；如果没有，且响应码支持拥有实体，并且使用的是HTTP 1.1，持久连接(Connection: keep-alive),那么我们将使用Transfer-Encoding：chunk。
@Override
protected final void prepareResponse() throws IOException {
boolean entityBody = true;
contentDelimitation = false;
OutputFilter[] outputFilters = outputBuffer.getFilters();
if (http09 == true) {
// HTTP/0.9
outputBuffer.addActiveFilter(outputFilters[Constants.IDENTITY_FILTER]);
outputBuffer.commit();
return;
}
int statusCode = response.getStatus();
if (statusCode < 200 || statusCode == 204 || statusCode == 205 ||
statusCode == 304) {
// No entity body
outputBuffer.addActiveFilter
(outputFilters[Constants.VOID_FILTER]);
entityBody = false;
contentDelimitation = true;
if (statusCode == 205) {
// RFC 7231 requires the server to explicitly signal an empty
// response in this case
response.setContentLength(0);
} else {
response.setContentLength(-1);
}
}
MessageBytes methodMB = request.method();
if (methodMB.equals("HEAD")) {
// No entity body
outputBuffer.addActiveFilter
(outputFilters[Constants.VOID_FILTER]);
contentDelimitation = true;
}
// Sendfile support
if (endpoint.getUseSendfile()) {
prepareSendfile(outputFilters);
}
// Check for compression
boolean isCompressible = false;
boolean useCompression = false;
if (entityBody && (compressionLevel > 0) && sendfileData == null) {
isCompressible = isCompressible();
if (isCompressible) {
useCompression = useCompression();
}
// Change content-length to -1 to force chunking
if (useCompression) {
response.setContentLength(-1);
}
}
MimeHeaders headers = response.getMimeHeaders();
// A SC_NO_CONTENT response may include entity headers
if (entityBody || statusCode == HttpServletResponse.SC_NO_CONTENT) {
String contentType = response.getContentType();
if (contentType != null) {
headers.setValue("Content-Type").setString(contentType);
}
String contentLanguage = response.getContentLanguage();
if (contentLanguage != null) {
headers.setValue("Content-Language")
.setString(contentLanguage);
}
}
long contentLength = response.getContentLengthLong();
boolean connectionClosePresent = false;
if (contentLength != -1) {
headers.setValue("Content-Length").setLong(contentLength);
outputBuffer.addActiveFilter
(outputFilters[Constants.IDENTITY_FILTER]);
contentDelimitation = true;
} else {
// If the response code supports an entity body and we're on
// HTTP 1.1 then we chunk unless we have a Connection: close header
connectionClosePresent = isConnectionClose(headers);
if (entityBody && http11 && !connectionClosePresent) {
outputBuffer.addActiveFilter
(outputFilters[Constants.CHUNKED_FILTER]);
contentDelimitation = true;
headers.addValue(Constants.TRANSFERENCODING).setString(Constants.CHUNKED);
} else {
outputBuffer.addActiveFilter
(outputFilters[Constants.IDENTITY_FILTER]);
}
}
if (useCompression) {
outputBuffer.addActiveFilter(outputFilters[Constants.GZIP_FILTER]);
headers.setValue("Content-Encoding").setString("gzip");
}
// If it might be compressed, set the Vary header
if (isCompressible) {
// Make Proxies happy via Vary (from mod_deflate)
MessageBytes vary = headers.getValue("Vary");
if (vary == null) {
// Add a new Vary header
headers.setValue("Vary").setString("Accept-Encoding");
} else if (vary.equals("*")) {
// No action required
} else {
// Merge into current header
headers.setValue("Vary").setString(
vary.getString() + ",Accept-Encoding");
}
}
// Add date header unless application has already set one (e.g. in a
// Caching Filter)
if (headers.getValue("Date") == null) {
headers.addValue("Date").setString(
FastHttpDateFormat.getCurrentDate());
}
// FIXME: Add transfer encoding header
if ((entityBody) && (!contentDelimitation)) {
// Mark as close the connection after the request, and add the
// connection: close header
keepAlive = false;
}
// This may disabled keep-alive to check before working out the
// Connection header.
checkExpectationAndResponseStatus();
// If we know that the request is bad this early, add the
// Connection: close header.
if (keepAlive && statusDropsConnection(statusCode)) {
keepAlive = false;
}
if (!keepAlive) {
// Avoid adding the close header twice
if (!connectionClosePresent) {
headers.addValue(Constants.CONNECTION).setString(
Constants.CLOSE);
}
} else if (!http11 && !getErrorState().isError()) {
headers.addValue(Constants.CONNECTION).setString(Constants.KEEPALIVE);
}
// Add server header
if (server == null) {
if (serverRemoveAppProvidedValues) {
headers.removeHeader("server");
}
} else {
// server always overrides anything the app might set
headers.setValue("Server").setString(server);
}
// Build the response header
try {
outputBuffer.sendStatus();
int size = headers.size();
for (int i = 0; i < size; i++) {
outputBuffer.sendHeader(headers.getName(i), headers.getValue(i));
}
outputBuffer.endHeaders();
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
// If something goes wrong, reset the header buffer so the error
// response can be written instead.
outputBuffer.resetHeaderBuffer();
throw t;
}
outputBuffer.commit();
}
private static boolean isConnectionClose(MimeHeaders headers) {
MessageBytes connection = headers.getValue(Constants.CONNECTION);
if (connection == null) {
return false;
}
return connection.equals(Constants.CLOSE);
}
private void prepareSendfile(OutputFilter[] outputFilters) {
String fileName = (String) request.getAttribute(
org.apache.coyote.Constants.SENDFILE_FILENAME_ATTR);
if (fileName == null) {
sendfileData = null;
} else {
// No entity body sent here
outputBuffer.addActiveFilter(outputFilters[Constants.VOID_FILTER]);
contentDelimitation = true;
long pos = ((Long) request.getAttribute(
org.apache.coyote.Constants.SENDFILE_FILE_START_ATTR)).longValue();
long end = ((Long) request.getAttribute(
org.apache.coyote.Constants.SENDFILE_FILE_END_ATTR)).longValue();
sendfileData = socketWrapper.createSendfileData(fileName, pos, end - pos);
}
}
2、写入响应内容
writeResponse():
private void writeResponse() throws Exception {
RequestContext context = RequestContext.getCurrentContext();
// there is no body to send
if (context.getResponseBody() == null
&& context.getResponseDataStream() == null) {
return;
}
HttpServletResponse servletResponse = context.getResponse();
if (servletResponse.getCharacterEncoding() == null) { // only set if not set
servletResponse.setCharacterEncoding("UTF-8");
}
OutputStream outStream = servletResponse.getOutputStream();
InputStream is = null;
try {
if (RequestContext.getCurrentContext().getResponseBody() != null) {
String body = RequestContext.getCurrentContext().getResponseBody();
writeResponse(
new ByteArrayInputStream(
body.getBytes(servletResponse.getCharacterEncoding())),
outStream);
return;
}
boolean isGzipRequested = false;
final String requestEncoding = context.getRequest()
.getHeader(ZuulHeaders.ACCEPT_ENCODING);
if (requestEncoding != null
&& HTTPRequestUtils.getInstance().isGzipped(requestEncoding)) {
isGzipRequested = true;
}
is = context.getResponseDataStream();
InputStream inputStream = is;
if (is != null) {
if (context.sendZuulResponse()) {
// if origin response is gzipped, and client has not requested gzip,
// decompress stream
// before sending to client
// else, stream gzip directly to client
if (context.getResponseGZipped() && !isGzipRequested) {
// If origin tell it's GZipped but the content is ZERO bytes,
// don't try to uncompress
final Long len = context.getOriginContentLength();
if (len == null || len > 0) {
try {
inputStream = new GZIPInputStream(is);
}
catch (java.util.zip.ZipException ex) {
log.debug(
"gzip expected but not "
+ "received assuming unencoded response "
+ RequestContext.getCurrentContext()
.getRequest().getRequestURL()
.toString());
inputStream = is;
}
}
else {
// Already done : inputStream = is;
}
}
else if (context.getResponseGZipped() && isGzipRequested) {
servletResponse.setHeader(ZuulHeaders.CONTENT_ENCODING, "gzip");
}
writeResponse(inputStream, outStream);
}
}
}
finally {
/**
* Closing the wrapping InputStream itself has no effect on closing the underlying tcp connection since it's a wrapped stream. I guess for http
* keep-alive. When closing the wrapping stream it tries to reach the end of the current request, which is impossible for infinite http streams. So
* instead of closing the InputStream we close the HTTP response.
*
* @author Johannes Edmeier
*/
try {
Object zuulResponse = RequestContext.getCurrentContext()
.get("zuulResponse");
if (zuulResponse instanceof Closeable) {
((Closeable) zuulResponse).close();
}
outStream.flush();
// The container will close the stream for us
}
catch (IOException ex) {
log.warn("Error while sending response to client: " + ex.getMessage());
}
}
}
private void writeResponse(InputStream zin, OutputStream out) throws Exception {
byte[] bytes = buffers.get();
int bytesRead = -1;
while ((bytesRead = zin.read(bytes)) != -1) {
out.write(bytes, 0, bytesRead);
}
}
由SimpleHostRoutingFilter可知，原始reponse获取的时候已将reponseBody或responseDataStream放入context中，它先判断是否存在responseBody，存在即写入输出流，直接返回，否则将responseDataStream写入，这里responseDataStream可能是一个压缩流，如果原始response是经过gzip压缩，而网关client没有要求gzip压缩，则在发送给客户端之前先解压响应流，否则就直接输出，并设置Content-Encoding:gzip头。
为了释放系统资源，前面通过route过滤器获取的reponse，即zuulResponse需要关闭，关闭其被包装InputStream也许只是为了保持http长连接，本身对底层tcp连接的关闭不起作用。因此，我们关闭HTTP响应而不是关闭InputStream。
先写到这里，有什么需要补充的请留言。
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ID：drjava
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