记录一下前段时间遇到的一个关于multipartResolver的异常,以及后面找出原因的过程。
异常分析
异常如下:
2018-01-22 18:05:38.041 ERROR com.exception.ExceptionHandler.resolveException:22 -Could not Q multipart servlet request; nested exception is org.apache.commons.fileupload.FileUploadBase$IOFileUploadException: Processing of multipart/form-data request failed. null
org.springframework.web.multipart.MultipartException: Could not parse multipart servlet request; nested exception is org.apache.commons.fileupload.FileUploadBase$IOFileUploadException: Processing of multipart/form-data request failed. null
at org.springframework.web.multipart.commons.CommonsMultipartResolver.parseRequest(CommonsMultipartResolver.java:165) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.multipart.commons.CommonsMultipartResolver.resolveMultipart(CommonsMultipartResolver.java:142) ~[spring-web-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.checkMultipart(DispatcherServlet.java:1089) [spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:928) [spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893) [spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:968) [spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:870) [spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:661) [servlet-api.jar:na]
at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:844) [spring-webmvc-4.2.5.RELEASE.jar:4.2.5.RELEASE]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) [servlet-api.jar:na]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) [catalina.jar:8.5.24]
at org.apache.catalina.core.A
这个异常大意是说multipart/form-data传输的表单存在空值,没有办法从request的表单中读到某个值。
确定了请求本身非空值之后,去看看是不是SpringMVC接收请求并从请求中读出参数的过程中出了问题。
那么,SpringMVC是如何处理请求传过来的文件的呢?
multipartResolver处理请求的过程
DispatcherServlet转发
首先,Spring提供了对文件多路上传的支持,只要注册一个名为”multipartResolver”的bean,那么后续SpringMVC的DispatcherServlet在接收到请求的时候,会判断请求是不是multipart文件。 如果是的话,就会调用”multipartResolver”,将请求包装成一个MultipartHttpServletRequest对象,然后后面就可以从这个对象中取出文件来进行处理了。
multipartResolver的装载
Spring提供了一个对于MultipartResolver接口的实现:org.springframework.web.multipart.commons.CommonsMultipartResolver。看一下源码:
public class CommonsMultipartResolver extends CommonsFileUploadSupport
implements MultipartResolver, ServletContextAware {
...
}
CommonsFileUploadSupport是对于XML配置”multipartResolver”时的支持。 在XML配置multipartResolver时的配置如下:
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
<!-- 默认编码 -->
<property name="defaultEncoding" value="utf-8" />
<!-- 设置multipart请求所允许的最大大小,默认不限制 -->
<property name="maxUploadSize" value="10485760000" />
<!-- 设置一个大小,multipart请求小于这个大小时会存到内存中,大于这个内存会存到硬盘中 -->
<property name="maxInMemorySize" value="40960" />
</bean>
这些property配置会被加载到CommonsFileUploadSupport中,然后被CommonsMultipartResolver继承。
CommonsMultipartResolver的处理过程
然后就是,其实CommonsMultipartResolver依赖于Apache的jar包来实现:common-fileupload。
CommonsMultipartResolver接收到请求之后,是这样对HttpServletReques进行处理的:
(CommonsMultipartResolver文件)
@Override
public MultipartHttpServletRequest resolveMultipart(final HttpServletRequest request) throws MultipartException {
Assert.notNull(request, "Request must not be null");
//懒加载
if (this.resolveLazily) {
return new DefaultMultipartHttpServletRequest(request) {
@Override
protected void initializeMultipart() {
MultipartParsingResult parsingResult = parseRequest(request);
setMultipartFiles(parsingResult.getMultipartFiles());
setMultipartParameters(parsingResult.getMultipartParameters());
setMultipartParameterContentTypes(parsingResult.getMultipartParameterContentTypes());
}
};
}
else {
//这里对request进行了解析
MultipartParsingResult parsingResult = parseRequest(request);
return new DefaultMultipartHttpServletRequest(request, parsingResult.getMultipartFiles(),
parsingResult.getMultipartParameters(), parsingResult.getMultipartParameterContentTypes());
}
}
this.resolveLazily是懒加载,如果为true,会在initializeMultipart()被调用,即发起文档信息获取的时候,才去封装DefaultMultipartHttpServletRequest;如果为false,立即封装DefaultMultipartHttpServletRequest。
resolveLazily默认为false。
然后再去看一下parseRequest(request)的解析:
(CommonsMultipartResolver文件)
/** * Parse the given servlet request, resolving its multipart elements. * 对servlet请求进行处理,转成multipart结构 * @param request the request to parse * @return the parsing result * @throws MultipartException if multipart resolution failed. */
protected MultipartParsingResult parseRequest(HttpServletRequest request) throws MultipartException {
//从请求中读出这个请求的编码
String encoding = determineEncoding(request);
//按照请求的编码,获取一个FileUpload对象,装载到CommonsFileUploadSupport的property属性都会被装入这个对象中
//prepareFileUpload是继承自CommonsFileUploadSupport的函数,会比较请求的编码和XML中配置的编码,如果不一样,会拒绝处理
FileUpload fileUpload = prepareFileUpload(encoding);
try {
//对请求中的multipart文件进行具体的处理
List<FileItem> fileItems = ((ServletFileUpload) fileUpload).parseRequest(request);
return parseFileItems(fileItems, encoding);
}
catch (FileUploadBase.SizeLimitExceededException ex) {
throw new MaxUploadSizeExceededException(fileUpload.getSizeMax(), ex);
}
catch (FileUploadException ex) {
throw new MultipartException("Could not parse multipart servlet request", ex);
}
}
上面的((ServletFileUpload) fileUpload).parseRequest(request)解析实现如下:
(FileUploadBase文件)
/** * Processes an <a href="http://www.ietf.org/rfc/rfc1867.txt">RFC 1867</a> * compliant <code>multipart/form-data</code> stream. * * @param ctx The context for the request to be parsed. * * @return A list of <code>FileItem</code> instances parsed from the * request, in the order that they were transmitted. * * @throws FileUploadException if there are problems reading/parsing * the request or storing files. */
public List<FileItem> parseRequest(RequestContext ctx)
throws FileUploadException {
List<FileItem> items = new ArrayList<FileItem>();
boolean successful = false;
try {
//从请求中取出multipart文件
FileItemFactoryFactoryFactoryator iter = getItemIterator(ctx);
//获得FileItemFactory工厂,实现类为DiskFileItemFactory
FileItemFactory fac = getFileItemFactory();
if (fac == null) {
throw new NullPointerException("No FileItemFactory has been set.");
}
while (iter.hasNext()) {
final FileItemStream item = iter.next();
// Don't use getName() here to prevent an InvalidFileNameException.
final String fileName = ((FileItemIteratorImpl.FileItemStreamImpl) item).name;
//工厂模式,获取FileItem对象,实现类是DiskFileItem
FileItem fileItem = fac.createItem(item.getFieldName(), item.getContentType(),
item.isFormField(), fileName);
items.add(fileItem);
try {
Streams.copy(item.openStream(), fileItem.getOutputStream(), true);
} catch (FileUploadIOException e) {
throw (FileUploadException) e.getCause();
} catch (IOException e) {
//我们遇到的异常就是在这里抛出的
throw new IOFileUploadException(format("Processing of %s request failed. %s",
MULTIPART_FORM_DATA, e.getMessage()), e);
}
final FileItemHeaders fih = item.getHeaders();
fileItem.setHeaders(fih);
}
successful = true;
return items;
} catch (FileUploadIOException e) {
throw (FileUploadException) e.getCause();
} catch (IOException e) {
throw new FileUploadException(e.getMessage(), e);
} finally {
if (!successful) {
for (FileItem fileItem : items) {
try {
fileItem.delete();
} catch (Throwable e) {
// ignore it
}
}
}
}
}
我们遇到的异常就是在这个位置抛出的,后面找错误会在这里深入,但是我们还是先把整个请求流转的流程走完。
到此,List对象就处理完返回了,然后再继续看对List的处理
(CommonsFileUploadSupport文件)
/** * Parse the given List of Commons FileItems into a Spring MultipartParsingResult, * containing Spring MultipartFile instances and a Map of multipart parameter. * @param fileItems the Commons FileIterms to parse * @param encoding the encoding to use for form fields * @return the Spring MultipartParsingResult * @see CommonsMultipartFile#CommonsMultipartFile(org.apache.commons.fileupload.FileItem) */
protected MultipartParsingResult parseFileItems(List<FileItem> fileItems, String encoding) {
MultiValueMap<String, MultipartFile> multipartFiles = new LinkedMultiValueMap<String, MultipartFile>();
Map<String, String[]> multipartParameters = new HashMap<String, String[]>();
Map<String, String> multipartParameterContentTypes = new HashMap<String, String>();
// Extract multipart files and multipart parameters.
for (FileItem fileItem : fileItems) {
//如果fileItem是一个表单
if (fileItem.isFormField()) {
String value;
String partEncoding = determineEncoding(fileItem.getContentType(), encoding);
if (partEncoding != null) {
try {
value = fileItem.getString(partEncoding);
}
catch (UnsupportedEncodingException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Could not decode multipart item '" + fileItem.getFieldName() +
"' with encoding '" + partEncoding + "': using platform default");
}
value = fileItem.getString();
}
}
else {
value = fileItem.getString();
}
String[] curParam = multipartParameters.get(fileItem.getFieldName());
if (curParam == null) {
// simple form field
multipartParameters.put(fileItem.getFieldName(), new String[] {value});
}
else {
// array of simple form fields
String[] newParam = StringUtils.addStringToArray(curParam, value);
multipartParameters.put(fileItem.getFieldName(), newParam);
}
multipartParameterContentTypes.put(fileItem.getFieldName(), fileItem.getContentType());
}
//如果fileItem是一个multipart文件
else {
// multipart file field
CommonsMultipartFile file = new CommonsMultipartFile(fileItem);
multipartFiles.add(file.getName(), file);
if (logger.isDebugEnabled()) {
logger.debug("Found multipart file [" + file.getName() + "] of size " + file.getSize() +
" bytes with original filename [" + file.getOriginalFilename() + "], stored " +
file.getStorageDescription());
}
}
}
return new MultipartParsingResult(multipartFiles, multipartParameters, multipartParameterContentTypes);
}
到此,MultipartParsingResult的处理就结束并返回了,然后CommonsMultipartResolver中的resolveMultipart就将其装到DefaultMultipartHttpServletRequest中并返回,处理完了。
DefaultMultipartHttpServletRequest是MultipartHttpServletRequest的实现类。
关于maxInMemorySize
前面已经说过,maxInMemorySize的作用是 “设置一个大小,multipart请求小于这个大小时会存到内存中,大于这个内存会存到硬盘中”。 再看一下maxInMemorySize被set到对象中的过程:
(CommonsFileUploadSupport文件)
/** * Set the maximum allowed size (in bytes) before uploads are written to disk. * Uploaded files will still be received past this amount, but they will not be * stored in memory. Default is 10240, according to Commons FileUpload. * @param maxInMemorySize the maximum in memory size allowed * @see org.apache.commons.fileupload.disk.DiskFileItemFactory#setSizeThreshold */
public void setMaxInMemorySize(int maxInMemorySize) {
this.fileItemFactory.setSizeThreshold(maxInMemorySize);
}
CommonsFileUploadSupport中有一个fileItemFactory对象,maxInMemorySize就被set到了这个工厂类的属性SizeThreshold里。
这个fileItemFactory工厂类,会在生成fileItem对象的时候用到。 生成这个对象的过程中,会根据maxInMemorySize来判断,是将其存到内存中,还是存到硬盘中。
存储的过程在前面已经提过了:
...
try {
Streams.copy(item.openStream(), fileItem.getOutputStream(), true);
} catch (FileUploadIOException e) {
throw (FileUploadException) e.getCause();
} catch (IOException e) {
throw new IOFileUploadException(format("Processing of %s request failed. %s",
MULTIPART_FORM_DATA, e.getMessage()), e);
}
final FileItemHeaders fih = item.getHeaders();
进入fileItem.getOutputStream()看看:
/** * Returns an {@link java.io.OutputStream OutputStream} that can * be used for storing the contents of the file. * * @return An {@link java.io.OutputStream OutputStream} that can be used * for storing the contensts of the file. * * @throws IOException if an error occurs. */
public OutputStream getOutputStream()
throws IOException {
if (dfos == null) {
File outputFile = getTempFile();
dfos = new DeferredFileOutputStream(sizeThreshold, outputFile);
}
return dfos;
}
再进去getTempFile():
/** * Creates and returns a {@link java.io.File File} representing a uniquely * named temporary file in the configured repository path. The lifetime of * the file is tied to the lifetime of the <code>FileItem</code> instance; * the file will be deleted when the instance is garbage collected. * * @return The {@link java.io.File File} to be used for temporary storage. */
protected File getTempFile() {
if (tempFile == null) {
File tempDir = repository;
if (tempDir == null) {
tempDir = new File(System.getProperty("java.io.tmpdir"));
}
String tempFileName = format("upload_%s_%s.tmp", UID, getUniqueId());
tempFile = new File(tempDir, tempFileName);
}
return tempFile;
}
当没有设置uploadTempDir属性,也就是FileItemFactory中的repository的时候会自动选择一个缓存路径System.getProperty(“java.io.tmpdir”),将上传请求落到硬盘上的这个位置。
注意看这个注释:the file will be deleted when the instance is garbage collected. 这里说了FileItem的实例声明周期,当GC的时候,存在内存里的FileItem会被GC回收掉。所以这就是为什么没有办法读到multipart/form-data对象。
bug原因和解决方案
- 解决频繁GC的问题。太过频繁的GC明显是出了问题了,导致请求中的文件被回收掉,报空指针。(这也是我这边解决问题的方案)
- 设置好maxInMemorySize和uploadTempDir两个属性,保证上传文件缓存到硬盘上,普通请求在内存中就可以了。如果涉及大量的文件上传,这个是很有必要的,不然并发高的时候,内存会被文件给占满。然后会触发GC,FileItem被回收掉之后,后面就会再去读取,就被出现我们异常中的空指针错误。
- 还有一种可能性,就是multipartResolver配置的时候,没有设置uploadTempDir属性。按理说这个是没有问题的,因为会默认帮你设为系统的缓存路径,这个路径通常是/tmp,这个目录所有用户都有权限读取。但是如果是生产环境,这个系统默认的缓存路径很可能会被修改过,修改了位置,或者权限。这也是为了安全的方面考虑,但是这在我们所讲的流程中,就会造成后面读取的时候,出现空指针的错误。
这些异常都不容易排查,所以需要对整个流程都清晰了之后,才容易找到问题的所在。单单看自己的代码是不能看出来的,例如权限的问题,在实际生产环境中才会遇到,也比较无奈。
我为什么要把这个问题写的这么复杂
把这个问题写了这么多,最后的解决方案却写的很少,看起来可能是很傻,但是是有原因的:
- 这个异常在网上没有找到有用的解决方案,也没有看到讲明白原因的
- 把流程理一遍,有利于后面遇到类似问题的时候,更好地解决。例如说不是报空值,而是报其他问题的时候。
- 最重要的一点,由于运行环境的原因,没有办法复现,也没有找到当时的堆栈信息,所以不得不整个流程都走了一遍……
今天的文章从multipartResolver的一个异常到multipartResolver处理请求过程分析分享到此就结束了,感谢您的阅读。
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