关于文件上传，我要向struts提点意见

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我是靠谱客的博主单纯书本，这篇文章主要介绍关于文件上传，我要向struts提点意见，现在分享给大家，希望可以做个参考。

前两天，公司一同事要做一个包含有文件上传的功能模块，问我采取哪种技术比较好。由于项目的技术架构是ssi，于是就建议他直接使用struts提供的FormFile。可是在他动手开发的过程中，却遇到了一些实际的问题，后来又找了我几次。最后我也专门想了想，其实struts提供的上传技术，虽然操作起来确实很简单，但是在某些方面却也存在一定的问题，使开发人员特别是新人很抓狂，甚至觉得无所适从。下面就简单聊一聊这些问题。

struts的上传其实就是对commons fileupload技术做了一个集成。在集成的过程中，像什么交换目录啊、文件大小控制啊之类的工作都帮我们完成了；而我们在使用的时候，这些问题都不需要考虑，甚至可能几行代码就搞定了。下面就是使用struts实现的一个简单的文件上传功能实例：

jsp页面：

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<form action="upload_action_form.do" method="post" enctype="multipart/form-data">
标题：<input type="text" name="title"><br>
文件：<input type="file" name="myfile"><br>
<input type="submit" value="提交">
</form>

Form类:

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import org.apache.struts.action.ActionForm;
import org.apache.struts.upload.FormFile;
/**
*
* @description：
* @author：  bruce.yang
* @date：2013-7-27 下午3:30:14
* @version v1.0
*
*/
public class UploadActionForm extends ActionForm {
private String title;
//必须用FormFile接收文件
private FormFile myfile;
//... ... getter,setter方法
}

Action类:

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/**
*
* @description：
* @author： bruce.yang
* @date：2013-7-27 下午3:32:45
* @version v1.0
*
*/
public class UploadAction2 extends Action {
@Override
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
UploadActionForm uaf = (UploadActionForm) form;
String title = uaf.getTitle();
System.out.println(title);
FileOutputStream fos = new FileOutputStream("d:\" + uaf.getMyfile().getFileName());
fos.write(uaf.getMyfile().getFileData());
fos.flush();
fos.close();
return mapping.findForward("upload");
}
}

结果页面ret_upload.jsp：

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<body>
上传成功！<br>
标题:${uploadForm.title}<br>
文件名:${uploadForm.myfile.fileName} }<br>
文件大小:${uploadForm.myfile.fileSize }<br>
文件类型:${uploadForm.myfile.contentType }
</body>

struts-config.xml：

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<struts-config>
<form-beans>
<form-bean name="uploadForm" type="com.bruceyang.struts.form.UploadActionForm"></form-bean>
</form-beans>
<action-mappings>
<action path="/upload_action_form"
type="com.bruceyang.struts.action.UploadAction"
name="uploadForm"
scope="request"
>
<forward name="upload" path="/ret_upload.jsp"></forward>
</action>
</action-mappings>
</struts-config>

web.xml想必大家都熟知，就不在这浪费篇幅了。

从上面代码中我们可以看到：struts使用FormFile来声明文件，我们在Action中直接操作FormFile实例就可以取得有关文件的数据、文件名、文件大小、上传类型等。而这只是在假设一切正常的情况下实现的，但是如果在实际运行中出现上传文件太大、服务器磁盘不足、enctype不对等异常情况时，
struts是怎么处理的呢？

从struts源码 org.apache.struts.config.ControllerConfig类

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/**
* The fully qualified Java class name of the MultipartRequestHandler
* class to be used.
*/
protected String multipartClass =
"org.apache.struts.upload.CommonsMultipartRequestHandler";
public String getMultipartClass() {
return (this.multipartClass);
}
public void setMultipartClass(String multipartClass) {
if (configured) {
throw new IllegalStateException("Configuration is frozen");
}
this.multipartClass = multipartClass;
}

可以看出,如果没有在配置文件中配置指定的处理类，那么struts处理文件上传的实现类是CommonsMultipartRequestHandler,那么查其源码：

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/**
* The default value for the maximum allowable size, in bytes, of an
* uploaded file. The value is equivalent to 250MB.
*/
public static final long DEFAULT_SIZE_MAX = 250 * 1024 * 1024;
/**
* The default value for the threshold which determines whether an uploaded
* file will be written to disk or cached in memory. The value is equivalent
* to 250KB.
*/
public static final int DEFAULT_SIZE_THRESHOLD = 256 * 1024;
//.......省略部分
/**
* Parses the input stream and partitions the parsed items into a set of
* form fields and a set of file items. In the process, the parsed items
* are translated from Commons FileUpload <code>FileItem</code> instances
* to Struts <code>FormFile</code> instances.
*
* @param request The multipart request to be processed.
*
* @throws ServletException if an unrecoverable error occurs.
*/
public void handleRequest(HttpServletRequest request)
throws ServletException {
// Get the app config for the current request.
ModuleConfig ac = (ModuleConfig) request.getAttribute(
Globals.MODULE_KEY);
// Create and configure a DIskFileUpload instance.
DiskFileUpload upload = new DiskFileUpload();
// The following line is to support an "EncodingFilter"
// see http://nagoya.apache.org/bugzilla/show_bug.cgi?id=23255
upload.setHeaderEncoding(request.getCharacterEncoding());
// Set the maximum size before a FileUploadException will be thrown.
upload.setSizeMax(getSizeMax(ac));
// Set the maximum size that will be stored in memory.
upload.setSizeThreshold((int) getSizeThreshold(ac));
// Set the the location for saving data on disk.
upload.setRepositoryPath(getRepositoryPath(ac));
// Create the hash tables to be populated.
elementsText = new Hashtable();
elementsFile = new Hashtable();
elementsAll = new Hashtable();
// Parse the request into file items.
List items = null;
try {
items = upload.parseRequest(request);
} catch (DiskFileUpload.SizeLimitExceededException e) {
// Special handling for uploads that are too big.
request.setAttribute(
MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED,
Boolean.TRUE);
return;
} catch (FileUploadException e) {
log.error("Failed to parse multipart request", e);
throw new ServletException(e);
}
// Partition the items into form fields and files.
Iterator iter = items.iterator();
while (iter.hasNext()) {
FileItem item = (FileItem) iter.next();
if (item.isFormField()) {
addTextParameter(request, item);
} else {
addFileParameter(item);
}
}
}

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/**
* The default value for the maximum allowable size, in bytes, of an
* uploaded file. The value is equivalent to 250MB.
*/
public static final long DEFAULT_SIZE_MAX = 250 * 1024 * 1024;
/**
* The default value for the threshold which determines whether an uploaded
* file will be written to disk or cached in memory. The value is equivalent
* to 250KB.
*/
public static final int DEFAULT_SIZE_THRESHOLD = 256 * 1024;
//.......省略部分
/**
* Parses the input stream and partitions the parsed items into a set of
* form fields and a set of file items. In the process, the parsed items
* are translated from Commons FileUpload <code>FileItem</code> instances
* to Struts <code>FormFile</code> instances.
*
* @param request The multipart request to be processed.
*
* @throws ServletException if an unrecoverable error occurs.
*/
public void handleRequest(HttpServletRequest request)
throws ServletException {
// Get the app config for the current request.
ModuleConfig ac = (ModuleConfig) request.getAttribute(
Globals.MODULE_KEY);
// Create and configure a DIskFileUpload instance.
DiskFileUpload upload = new DiskFileUpload();
// The following line is to support an "EncodingFilter"
// see http://nagoya.apache.org/bugzilla/show_bug.cgi?id=23255
upload.setHeaderEncoding(request.getCharacterEncoding());
// Set the maximum size before a FileUploadException will be thrown.
upload.setSizeMax(getSizeMax(ac));
// Set the maximum size that will be stored in memory.
upload.setSizeThreshold((int) getSizeThreshold(ac));
// Set the the location for saving data on disk.
upload.setRepositoryPath(getRepositoryPath(ac));
// Create the hash tables to be populated.
elementsText = new Hashtable();
elementsFile = new Hashtable();
elementsAll = new Hashtable();
// Parse the request into file items.
List items = null;
try {
items = upload.parseRequest(request);
} catch (DiskFileUpload.SizeLimitExceededException e) {
// Special handling for uploads that are too big.
request.setAttribute(
MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED,
Boolean.TRUE);
return;
} catch (FileUploadException e) {
log.error("Failed to parse multipart request", e);
throw new ServletException(e);
}
// Partition the items into form fields and files.
Iterator iter = items.iterator();
while (iter.hasNext()) {
FileItem item = (FileItem) iter.next();
if (item.isFormField()) {
addTextParameter(request, item);
} else {
addFileParameter(item);
}
}
}

可以看出，struts默认处理上传文件最大是250M，而一旦上传文件过大超过了最大值，struts仅仅是在request的Attribute中添加属性值对MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED-Boolean.TRUE,并未将异常情况带回到Action！struts这种“极其不负责任”的行为直接导致了，开发人员不知道在什么时候告诉用户他传的文件过大了！即使可以在struts的配置文件中指定上传文件的最大值。更过分的是，对于上传过程中出现的其它问题，struts压根就没有去处理它，而是在自己的日志中记录了一下，就直接抛给了上一层了。

而对开发人员而言，有时候是一定要获得这些（甚至是全部）异常，该咋办呢？

对不起，您只有自己定制MultipartRequestHandler了。由于时间的关系，我没有定制该类，在这里仅给大家提供个思路，希望朋友们，能够帮我完成并恳请与我交流。在写之前，您务必明白commons-fileupload上传控件在上传过程中到底可能抛出那些异常？那么在定制MultipartRequestHandler.handleRequest的时候，你使用try/catch尽可能的捕获所有异常，并放到request的attribute里去就哦了。完了之后，在struts-config.xml中使用<controller>标签指定让struts使用你的处理类。这样，我们再用FormFile上传文件，一旦上传过程中出现了异常，就会被写入request的attributs里。而在action类中，只需要获取各种异常信息，即可随时做相应处理并给用户返回相应的提示。

时间关系,我在那个项目中是向 struts做了妥协，并没有定制新的MultipartRequestHandler，而只是获取了MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED来判断文件是否过大，对于其他的异常信息，一律作为上传失败处理，类似：

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/**
*
* @description：
* @author： bruce.yang
* @date：2013-7-27 下午3:32:45
* @version v1.0
*
*/
public class UploadAction extends Action {
@Override
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
try {
UploadActionForm uaf = (UploadActionForm) form;
String title = uaf.getTitle();
System.out.println(title);
if (request.getAttribute(MultipartRequestHandler.ATTRIBUTE_MAX_LENGTH_EXCEEDED) != null) {
request.setAttribute("msg", "文件大于5M，上传失败!");
return mapping.findForward("fail");
}
FileOutputStream fos = new FileOutputStream("d:\" + uaf.getMyfile().getFileName());
fos.write(uaf.getMyfile().getFileData());
fos.flush();
fos.close();
return mapping.findForward("upload");
} catch (Exception e) {
request.setAttribute("msg", " 抱歉，上传出错，请稍后再试。");
return mapping.findForward("fail");
}
}
}