本文深入剖析了Tomcat服务器如何解析HTTP请求中的表单参数，涵盖了multipart/form-data和application/x-www-form-urlencoded两种content-type的处理流程。通过源码解读，揭示了参数解析的核心机制，包括字符集设置、参数限制检查及异常处理。
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核心类： /home/cmj/.m2/repository/org/apache/tomcat/embed/tomcat-embed-core/9.0.16/tomcat-embed-core-9.0.16-sources.jar!/org/apache/catalina/connector/Request.java:3276
/**
* Parse request parameters.
*/
protected void parseParameters() {
parametersParsed = true;
Parameters parameters = coyoteRequest.getParameters();
boolean success = false;
try {
// Set this every time in case limit has been changed via JMX
parameters.setLimit(getConnector().getMaxParameterCount());
// getCharacterEncoding() may have been overridden to search for
// hidden form field containing request encoding
Charset charset = getCharset();
boolean useBodyEncodingForURI = connector.getUseBodyEncodingForURI();
parameters.setCharset(charset);
if (useBodyEncodingForURI) {
parameters.setQueryStringCharset(charset);
}
// Note: If !useBodyEncodingForURI, the query string encoding is
// that set towards the start of CoyoyeAdapter.service()
parameters.handleQueryParameters();
if (usingInputStream || usingReader) {
success = true;
return;
}
//获取上下文类型，根据类型解析
String contentType = getContentType();
if (contentType == null) {
contentType = "";
}
int semicolon = contentType.indexOf(';');
if (semicolon >= 0) {
contentType = contentType.substring(0, semicolon).trim();
} else {
contentType = contentType.trim();
}
if ("multipart/form-data".equals(contentType)) { //多表单数据
parseParts(false);
success = true;
return;
}
if( !getConnector().isParseBodyMethod(getMethod()) ) {
success = true;
return;
}
//url拼接的参数,也属于表单数据,如果是url表单数据,则进行解析,否则返回return;
if (!("application/x-www-form-urlencoded".equals(contentType))) {
success = true;
return;
}
int len = getContentLength();
if (len > 0) {
int maxPostSize = connector.getMaxPostSize();
if ((maxPostSize >= 0) && (len > maxPostSize)) {
Context context = getContext();
if (context != null && context.getLogger().isDebugEnabled()) {
context.getLogger().debug(
sm.getString("coyoteRequest.postTooLarge"));
}
checkSwallowInput();
parameters.setParseFailedReason(FailReason.POST_TOO_LARGE); //失败理由 url过长
return;
}
byte[] formData = null;
if (len < CACHED_POST_LEN) {
if (postData == null) {
postData = new byte[CACHED_POST_LEN];
}
formData = postData;
} else {
formData = new byte[len];
}
try {
if (readPostBody(formData, len) != len) {
parameters.setParseFailedReason(FailReason.REQUEST_BODY_INCOMPLETE);//失败body 数据不完整
return;
}
} catch (IOException e) {
// Client disconnect
Context context = getContext();
if (context != null && context.getLogger().isDebugEnabled()) {
context.getLogger().debug(
sm.getString("coyoteRequest.parseParameters"),
e);
}
parameters.setParseFailedReason(FailReason.CLIENT_DISCONNECT);//失败理由客户端断开链接
return;
}
parameters.processParameters(formData, 0, len); //开始解析 form表单参数
} else if ("chunked".equalsIgnoreCase(
coyoteRequest.getHeader("transfer-encoding"))) {
byte[] formData = null;
try {
formData = readChunkedPostBody();
} catch (IllegalStateException ise) {
// chunkedPostTooLarge error
parameters.setParseFailedReason(FailReason.POST_TOO_LARGE);//失败理由: 太长
Context context = getContext();
if (context != null && context.getLogger().isDebugEnabled()) {
context.getLogger().debug(
sm.getString("coyoteRequest.parseParameters"),
ise);
}
return;
} catch (IOException e) {
// Client disconnect
parameters.setParseFailedReason(FailReason.CLIENT_DISCONNECT);//客户端断开链接
Context context = getContext();
if (context != null && context.getLogger().isDebugEnabled()) {
context.getLogger().debug(
sm.getString("coyoteRequest.parseParameters"),
e);
}
return;
}
if (formData != null) {
parameters.processParameters(formData, 0, formData.length); //处理form数据
}
}
success = true;
} finally {
if (!success) {
parameters.setParseFailedReason(FailReason.UNKNOWN);
}
}
}
private void parseParts(boolean explicit) {
// Return immediately if the parts have already been parsed
if (parts != null || partsParseException != null) {
return;
}
Context context = getContext();
MultipartConfigElement mce = getWrapper().getMultipartConfigElement();
if (mce == null) {
if(context.getAllowCasualMultipartParsing()) {
mce = new MultipartConfigElement(null,
connector.getMaxPostSize(),
connector.getMaxPostSize(),
connector.getMaxPostSize());
} else {
if (explicit) {
partsParseException = new IllegalStateException(
sm.getString("coyoteRequest.noMultipartConfig"));
return;
} else {
parts = Collections.emptyList();
return;
}
}
}
Parameters parameters = coyoteRequest.getParameters();
parameters.setLimit(getConnector().getMaxParameterCount());
boolean success = false;
try {
File location;
String locationStr = mce.getLocation();
if (locationStr == null || locationStr.length() == 0) {
location = ((File) context.getServletContext().getAttribute(
ServletContext.TEMPDIR));
} else {
// If relative, it is relative to TEMPDIR
location = new File(locationStr);
if (!location.isAbsolute()) {
location = new File(
(File) context.getServletContext().getAttribute(
ServletContext.TEMPDIR),
locationStr).getAbsoluteFile();
}
}
if (!location.isDirectory()) {
parameters.setParseFailedReason(FailReason.MULTIPART_CONFIG_INVALID);
partsParseException = new IOException(
sm.getString("coyoteRequest.uploadLocationInvalid",
location));
return;
}
// Create a new file upload handler
DiskFileItemFactory factory = new DiskFileItemFactory();
try {
factory.setRepository(location.getCanonicalFile());
} catch (IOException ioe) {
parameters.setParseFailedReason(FailReason.IO_ERROR);
partsParseException = ioe;
return;
}
factory.setSizeThreshold(mce.getFileSizeThreshold());
ServletFileUpload upload = new ServletFileUpload();
upload.setFileItemFactory(factory);
upload.setFileSizeMax(mce.getMaxFileSize());
upload.setSizeMax(mce.getMaxRequestSize());
parts = new ArrayList<>();
try {
List<FileItem> items =
upload.parseRequest(new ServletRequestContext(this));
int maxPostSize = getConnector().getMaxPostSize();
int postSize = 0;
Charset charset = getCharset();
for (FileItem item : items) {
ApplicationPart part = new ApplicationPart(item, location);
parts.add(part); //关键代码 封装part, request.getParts() 可以获取
if (part.getSubmittedFileName() == null) {
String name = part.getName();
String value = null;
try {
value = part.getString(charset.name()); //如果是表单数据,则解析他的值
} catch (UnsupportedEncodingException uee) {
// Not possible
}
if (maxPostSize >= 0) {
// Have to calculate equivalent size. Not completely
// accurate but close enough.
postSize += name.getBytes(charset).length;
if (value != null) {
// Equals sign
postSize++;
// Value length
postSize += part.getSize();
}
// Value separator
postSize++;
if (postSize > maxPostSize) {
parameters.setParseFailedReason(FailReason.POST_TOO_LARGE);
throw new IllegalStateException(sm.getString(
"coyoteRequest.maxPostSizeExceeded"));
}
}
parameters.addParameter(name, value);//放入值,request.getParameter("name")可以获取
}
}
success = true;
} catch (InvalidContentTypeException e) {
parameters.setParseFailedReason(FailReason.INVALID_CONTENT_TYPE);
partsParseException = new ServletException(e);
} catch (FileUploadBase.SizeException e) {
parameters.setParseFailedReason(FailReason.POST_TOO_LARGE);
checkSwallowInput();
partsParseException = new IllegalStateException(e);
} catch (FileUploadException e) {
parameters.setParseFailedReason(FailReason.IO_ERROR);
partsParseException = new IOException(e);
} catch (IllegalStateException e) {
// addParameters() will set parseFailedReason
checkSwallowInput();
partsParseException = e;
}
} finally {
// This might look odd but is correct. setParseFailedReason() only
// sets the failure reason if none is currently set. This code could
// be more efficient but it is written this way to be robust with
// respect to changes in the remainder of the method.
if (partsParseException != null || !success) {
parameters.setParseFailedReason(FailReason.UNKNOWN);
}
}
}
// 解析 url中的参数
private void processParameters(byte bytes[], int start, int len, Charset charset) {
if(log.isDebugEnabled()) {
log.debug(sm.getString("parameters.bytes",
new String(bytes, start, len, DEFAULT_BODY_CHARSET)));
}
int decodeFailCount = 0;
int pos = start;
int end = start + len;
while(pos < end) {
int nameStart = pos;
int nameEnd = -1;
int valueStart = -1;
int valueEnd = -1;
boolean parsingName = true;
boolean decodeName = false;
boolean decodeValue = false;
boolean parameterComplete = false;
do {
switch(bytes[pos]) {
case '=':
if (parsingName) {
// Name finished. Value starts from next character
nameEnd = pos;
parsingName = false;
valueStart = ++pos;
} else {
// Equals character in value
pos++;
}
break;
case '&':
if (parsingName) {
// Name finished. No value.
nameEnd = pos;
} else {
// Value finished
valueEnd = pos;
}
parameterComplete = true;
pos++;
break;
case '%':
case '+':
// Decoding required
if (parsingName) {
decodeName = true;
} else {
decodeValue = true;
}
pos ++;
break;
default:
pos ++;
break;
}
} while (!parameterComplete && pos < end);
if (pos == end) {
if (nameEnd == -1) {
nameEnd = pos;
} else if (valueStart > -1 && valueEnd == -1){
valueEnd = pos;
}
}
if (log.isDebugEnabled() && valueStart == -1) {
log.debug(sm.getString("parameters.noequal",
Integer.valueOf(nameStart), Integer.valueOf(nameEnd),
new String(bytes, nameStart, nameEnd-nameStart, DEFAULT_BODY_CHARSET)));
}
if (nameEnd <= nameStart ) {
if (valueStart == -1) {
// &&
if (log.isDebugEnabled()) {
log.debug(sm.getString("parameters.emptyChunk"));
}
// Do not flag as error
continue;
}
// &=foo&
UserDataHelper.Mode logMode = userDataLog.getNextMode();
if (logMode != null) {
String extract;
if (valueEnd > nameStart) {
extract = new String(bytes, nameStart, valueEnd - nameStart,
DEFAULT_BODY_CHARSET);
} else {
extract = "";
}
String message = sm.getString("parameters.invalidChunk",
Integer.valueOf(nameStart),
Integer.valueOf(valueEnd), extract);
switch (logMode) {
case INFO_THEN_DEBUG:
message += sm.getString("parameters.fallToDebug");
//$FALL-THROUGH$
case INFO:
log.info(message);
break;
case DEBUG:
log.debug(message);
}
}
setParseFailedReason(FailReason.NO_NAME);//解析失败没有name
continue;
// invalid chunk - it's better to ignore
}
tmpName.setBytes(bytes, nameStart, nameEnd - nameStart);
if (valueStart >= 0) {
tmpValue.setBytes(bytes, valueStart, valueEnd - valueStart);
} else {
tmpValue.setBytes(bytes, 0, 0);
}
// Take copies as if anything goes wrong originals will be
// corrupted. This means original values can be logged.
// For performance - only done for debug
if (log.isDebugEnabled()) {
try {
origName.append(bytes, nameStart, nameEnd - nameStart);
if (valueStart >= 0) {
origValue.append(bytes, valueStart, valueEnd - valueStart);
} else {
origValue.append(bytes, 0, 0);
}
} catch (IOException ioe) {
// Should never happen...
log.error(sm.getString("parameters.copyFail"), ioe);
}
}
try {
String name;
String value;
if (decodeName) {
urlDecode(tmpName);
}
tmpName.setCharset(charset);
name = tmpName.toString();
if (valueStart >= 0) {
if (decodeValue) {
urlDecode(tmpValue);
}
tmpValue.setCharset(charset);
value = tmpValue.toString();
} else {
value = "";
}
try {
addParameter(name, value); //添加到param中, 可以request.getParameter("name") 获取
} catch (IllegalStateException ise) {
// Hitting limit stops processing further params but does
// not cause request to fail.
UserDataHelper.Mode logMode = maxParamCountLog.getNextMode();
if (logMode != null) {
String message = ise.getMessage();
switch (logMode) {
case INFO_THEN_DEBUG:
message += sm.getString(
"parameters.maxCountFail.fallToDebug");
//$FALL-THROUGH$
case INFO:
log.info(message);
break;
case DEBUG:
log.debug(message);
}
}
break;
}
} catch (IOException e) {
setParseFailedReason(FailReason.URL_DECODING);//url解码异常
decodeFailCount++;
if (decodeFailCount == 1 || log.isDebugEnabled()) {
if (log.isDebugEnabled()) {
log.debug(sm.getString("parameters.decodeFail.debug",
origName.toString(), origValue.toString()), e);
} else if (log.isInfoEnabled()) {
UserDataHelper.Mode logMode = userDataLog.getNextMode();
if (logMode != null) {
String message = sm.getString(
"parameters.decodeFail.info",
tmpName.toString(), tmpValue.toString());
switch (logMode) {
case INFO_THEN_DEBUG:
message += sm.getString("parameters.fallToDebug");
//$FALL-THROUGH$
case INFO:
log.info(message);
break;
case DEBUG:
log.debug(message);
}
}
}
}
}
tmpName.recycle();
tmpValue.recycle();
// Only recycle copies if we used them
if (log.isDebugEnabled()) {
origName.recycle();
origValue.recycle();
}
}
if (decodeFailCount > 1 && !log.isDebugEnabled()) {
UserDataHelper.Mode logMode = userDataLog.getNextMode();
if (logMode != null) {
String message = sm.getString(
"parameters.multipleDecodingFail",
Integer.valueOf(decodeFailCount));
switch (logMode) {
case INFO_THEN_DEBUG:
message += sm.getString("parameters.fallToDebug");
//$FALL-THROUGH$
case INFO:
log.info(message);
break;
case DEBUG:
log.debug(message);
}
}
}
}
以上为form表单解析源码. 主要针对content-type为: multipart/form-data 和 application/x-www-form-urlencoded. 可以request.getParameter(“name”) 获取.
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