struts2 使用 jakarta 上传文件时commons fileupload的异常捕捉

问题：

        struts2 使用jakarta 上传文件时，如果上传文件的大小超出commons fileupload(jakarta上传文件还是依赖commons-fileupload)设置的大小就会在进入action以前抛出异常.
        如果想返回用户的输入界面（input）,那么页面原来的参数会丢失。

首先看一下struts2 执行一个action的过程

1.  将用户请求发给org.apache.struts2.dispatcher.Dispatcher，
     wrapRequest(HttpServletRequest request, ServletContext servletContext)  方法会判断是否"multipart/form-data"，如果是建立一个multiPartRequest 的实例，并且建立MultiPartRequestWrapper

2. 建立 MultiPartRequestWrapper 时解析(parse) request,

public void parse(HttpServletRequest servletRequest, String saveDir)
            throws IOException {
        DiskFileItemFactory fac = new DiskFileItemFactory();
        // Make sure that the data is written to file
        fac.setSizeThreshold(0);
        if (saveDir != null) {
            fac.setRepository(new File(saveDir));
        }

        // Parse the request
        try {
            ServletFileUpload upload = new ServletFileUpload(fac);
            upload.setSizeMax(maxSize);
            //upload 解析request并取得页面参数
 	    List items = upload.parseRequest(createRequestContext(servletRequest));
 		......
	    

 3.我们看一下ServletFileUpload(commons-fileupload v1.1.1) 的parseRequest做了什么

 public List /* FileItem */ parseRequest(RequestContext ctx)
            throws FileUploadException {
        if (ctx == null) {
            throw new NullPointerException("ctx parameter");
        }

        ArrayList items = new ArrayList();
        String contentType = ctx.getContentType();

        if ((null == contentType)
            || (!contentType.toLowerCase().startsWith(MULTIPART))) {
            throw new InvalidContentTypeException(
                "the request doesn't contain a "
                + MULTIPART_FORM_DATA
                + " or "
                + MULTIPART_MIXED
                + " stream, content type header is "
                + contentType);
        }
        int requestSize = ctx.getContentLength();
        
        if (requestSize == -1) {
            throw new UnknownSizeException(
                "the request was rejected because its size is unknown");
        }
        //关键就这里了，大小超出的异常，这里是所有上传文件合计的大小，如果超出就抛出异常
        //这时上层是拿不到保存参数的items的
        if (sizeMax >= 0 && requestSize > sizeMax) {
            throw new SizeLimitExceededException(
                "the request was rejected because its size (" + requestSize
                + ") exceeds the configured maximum (" + sizeMax + ")",
                requestSize, sizeMax);
        }

        String charEncoding = headerEncoding;
        if (charEncoding == null) {
            charEncoding = ctx.getCharacterEncoding();
        }

        try {
            byte[] boundary = getBoundary(contentType);
            if (boundary == null) {
                throw new FileUploadException(
                        "the request was rejected because "
                        + "no multipart boundary was found");
            }

            InputStream input = ctx.getInputStream();

            MultipartStream multi = new MultipartStream(input, boundary);
            multi.setHeaderEncoding(charEncoding);

            boolean nextPart = multi.skipPreamble();
            while (nextPart) {
                Map headers = parseHeaders(multi.readHeaders());
                String fieldName = getFieldName(headers);
                if (fieldName != null) {
                    String subContentType = getHeader(headers, CONTENT_TYPE);
                    if (subContentType != null && subContentType
                        .toLowerCase().startsWith(MULTIPART_MIXED)) {
                        // Multiple files.
                        byte[] subBoundary = getBoundary(subContentType);
                        multi.setBoundary(subBoundary);
                        boolean nextSubPart = multi.skipPreamble();
                        while (nextSubPart) {
                            headers = parseHeaders(multi.readHeaders());
                            if (getFileName(headers) != null) {
                                FileItem item =
                                        createItem(headers, false);
                                OutputStream os = item.getOutputStream();
                                try {
                                    multi.readBodyData(os);
                                } finally {
                                    os.close();
                                }
                                items.add(item);
                            } else {
                                // Ignore anything but files inside
                                // multipart/mixed.
                                multi.discardBodyData();
                            }
                            nextSubPart = multi.readBoundary();
                        }
                        multi.setBoundary(boundary);
                    } else {
                        FileItem item = createItem(headers,
                                getFileName(headers) == null);
                        OutputStream os = item.getOutputStream();
                        try {
                            multi.readBodyData(os);
                        } finally {
                            os.close();
                        }
                        items.add(item);
                    }
                } else {
                    // Skip this part.
                    multi.discardBodyData();
                }
                nextPart = multi.readBoundary();
            }
        } catch (IOException e) {
            throw new FileUploadException(
                "Processing of " + MULTIPART_FORM_DATA
                    + " request failed. " + e.getMessage());
        }

        return items;
    }

 4.这之后才开始逐个进入interceptor,见DefaultActionInvocation.invoke()

....
//递归interceptor
if (interceptors.hasNext()) {
    			final InterceptorMapping interceptor = (InterceptorMapping) interceptors.next();
    			UtilTimerStack.profile("interceptor: "+interceptor.getName(), 
    					new UtilTimerStack.ProfilingBlock<String>() {
							public String doProfiling() throws Exception {
				    			resultCode = interceptor.getInterceptor().intercept(DefaultActionInvocation.this);
				    			return null;
							}
    			});
    		} else {
                        //如果有errors,resultCode会得到‘input’
    			resultCode = invokeActionOnly();
    		}
...

 5.我们的目标就是返回input并且保留页面原来的参数，那么就要不要让ServletFileUpload抛出异常，并且要让strusts使用我们自己的jakart.

 6.写自己的ServletFileUpload

/*
 * Copyright 2001-2005 The Apache Software Foundation
 *
 * 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 com.infowarelab.newcentury.web.util;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.FileItemFactory;
import org.apache.commons.fileupload.FileUpload;
import org.apache.commons.fileupload.FileUploadException;
import org.apache.commons.fileupload.MultipartStream;
import org.apache.commons.fileupload.RequestContext;
import org.apache.commons.fileupload.servlet.ServletRequestContext;
import org.apache.log4j.Logger;

/**
  * come from commons-fileupload
  * @author alfred
 */
public class ServletFileUpload extends FileUpload {

	// ---------------------------------------------------------- Class methods

	/**
	 * Logger for this class
	 */
	private static final Logger logger = Logger.getLogger(ServletFileUpload.class);
	private List<String> errors = new ArrayList<String>();

	/**
	 * Constructs an uninitialised instance of this class. A factory must be
	 * configured, using <code>setFileItemFactory()</code>, before attempting
	 * to parse requests.
	 * 
	 * @see FileUpload#FileUpload(FileItemFactory)
	 */
	public ServletFileUpload() {
		super();
	}

	/**
	 * Constructs an instance of this class which uses the supplied factory to
	 * create <code>FileItem</code> instances.
	 * 
	 * @see FileUpload#FileUpload()
	 */
	public ServletFileUpload(FileItemFactory fileItemFactory) {
		super(fileItemFactory);
	}
	/**
	 * overide parseRequest
	 */
	public List /* FileItem */parseRequest(RequestContext ctx) throws FileUploadException {
		if (ctx == null) {
			throw new NullPointerException("ctx parameter");
		}

		ArrayList items = new ArrayList();
		String contentType = ctx.getContentType();

		if ((null == contentType) || (!contentType.toLowerCase().startsWith(MULTIPART))) {
			throw new InvalidContentTypeException("the request doesn't contain a " + MULTIPART_FORM_DATA + " or "
					+ MULTIPART_MIXED + " stream, content type header is " + contentType);
		}
		int requestSize = ctx.getContentLength();

		if (requestSize == -1) {
			// throw new UnknownSizeException(
			// "the request was rejected because its size is unknown");
			logger.error("the request was rejected because its size is unknown");
			errors.add("the request was rejected because its size is unknown");
		}

		String charEncoding = getHeaderEncoding();
		if (charEncoding == null) {
			charEncoding = ctx.getCharacterEncoding();
		}

		try {
			byte[] boundary = getBoundary(contentType);
			if (boundary == null) {
				// throw new FileUploadException(
				// "the request was rejected because "
				// + "no multipart boundary was found");
				logger.error("the request was rejected because no multipart boundary was found");
				errors.add("the request was rejected because no multipart boundary was found");
			}

			InputStream input = ctx.getInputStream();

			MultipartStream multi = new MultipartStream(input, boundary);
			multi.setHeaderEncoding(charEncoding);

			boolean nextPart = multi.skipPreamble();
			while (nextPart) {
				Map headers = parseHeaders(multi.readHeaders());
				String fieldName = getFieldName(headers);
				if (fieldName != null) {
					String subContentType = getHeader(headers, CONTENT_TYPE);
					if (subContentType != null && subContentType.toLowerCase().startsWith(MULTIPART_MIXED)) {
						// Multiple files.
						byte[] subBoundary = getBoundary(subContentType);
						multi.setBoundary(subBoundary);
						boolean nextSubPart = multi.skipPreamble();
						while (nextSubPart) {
							headers = parseHeaders(multi.readHeaders());
							if (getFileName(headers) != null) {
								FileItem item = createItem(headers, false);
								OutputStream os = item.getOutputStream();
								try {
									multi.readBodyData(os);
								} finally {
									os.close();
								}
								items.add(item);
							} else {
								// Ignore anything but files inside
								// multipart/mixed.
								multi.discardBodyData();
							}
							nextSubPart = multi.readBoundary();
						}
						multi.setBoundary(boundary);
					} else {
						FileItem item = createItem(headers, getFileName(headers) == null);
						OutputStream os = item.getOutputStream();
						try {
							multi.readBodyData(os);
						} finally {
							os.close();
						}
						items.add(item);
					}
				} else {
					// Skip this part.
					multi.discardBodyData();
				}
				nextPart = multi.readBoundary();
			}
			// remove SizeLimitExceededException
			if (getSizeMax() >= 0 && requestSize > getSizeMax()) {
				// throw new SizeLimitExceededException(
				// "the request was rejected because its size (" + requestSize
				// + ") exceeds the configured maximum (" + getSizeMax() + ")",
				// requestSize, getSizeMax());
				logger.error("the request was rejected because its size (" + requestSize
						+ ") exceeds the configured maximum (" + getSizeMax() + ")");
			}
		} catch (IOException e) {
			logger.error("Processing of " + MULTIPART_FORM_DATA + " request failed. " + e.getMessage());
			errors.add("Processing of " + MULTIPART_FORM_DATA + " request failed. " + e.getMessage());
			// throw new FileUploadException(
			// "Processing of " + MULTIPART_FORM_DATA
			// + " request failed. " + e.getMessage());
		} 
		
		return items;
	}

	/**
	 * @return the errors
	 */
	public List<String> getErrors() {
		return errors;
	}

	/**
	 * @param errors the errors to set
	 */
	public void setErrors(List<String> errors) {
		this.errors = errors;
	}

}

7.copy org.apache.struts2.dispatcher.multipart.JakartaMultiPartRequest，只是import上面自己的ServletFileUpload.这样就可以保存页面的所有参数了。

8.更改struts配置文件加入你自己的JakartaMultiReques

 <bean type="org.apache.struts2.dispatcher.multipart.MultiPartRequest" 
name="jakarta_yourself" 
        class="com.xxxxx.util.JakartaMultiPartRequest" 
scope="default" optional="true" />

 9.更改struts.properties

struts.multipart.parser=jakarta_yourself

10.就OK啦