common-fileupload 分析

以前项目里面都经常用到上传的功能，从最早的smartFileUpload到apache 的common-fileupload.但是运用归运用，还是要了解实质才行，下面以common-fileupload为例子来讲解

首先要了解上传的本质，首先上传需要在jsp页面的form标签中配置enctype="multipart/form-data"

因为这样配置后，在http请求发出时才会以2进制的方式去传输上传文件

 

当请求到达服务端后，在action我们的代码是

DiskFileItemFactory factory = new DiskFileItemFactory();
// 当文件大小超过300k时，就在磁盘上建立临时文件
factory.setSizeThreshold(300000);
//设计文件上传的临时目录
factory.setRepository(new File("D:\\temp"));
ServletFileUpload upload = new ServletFileUpload(factory);
// 文件大小不能超过20M
upload.setSizeMax(20000000);

 

用struts2做上传的朋友都知道，在struts2的property文件中可以配置上传文件大小和上传的临时文件目录，其实struts2也是这样的实现

 

在这里我们同时还可以使用upload.setProgressListener(new ProgressListener())来监控上传的进度，一般情况下都是采用ajax来同步客户端和服务端的数据

具体可以参考：http://www.ibm.com/developerworks/cn/opensource/os-cn-agajax/

 

在设定好了一系列参数后，我们就要开始主要的方法了

ServletFileUpload.parseRequest(Request  request)

 

  public List /* FileItem */ parseRequest(HttpServletRequest request)
    throws FileUploadException {
        return parseRequest(new ServletRequestContext(request));
    }

 

 

 public List /* FileItem */ parseRequest(RequestContext ctx)
            throws FileUploadException {
        try {
            FileItemIterator iter = getItemIterator(ctx);//这个方法是相当重要的，在下面介绍
            List items = new ArrayList();
            FileItemFactory fac = getFileItemFactory();
            if (fac == null) {
                throw new NullPointerException(
                    "No FileItemFactory has been set.");
            }
            while (iter.hasNext()) {
                FileItemStream item = iter.next();
                FileItem fileItem = fac.createItem(item.getFieldName(),
                        item.getContentType(), item.isFormField(),
                        item.getName());
                try {
//将2个流copy，item.openStream()是request中的流，fileItem.getOutputStream()是准备向指定上传文件夹写文件的流
//fileItem.getOutputStream() 中就设定了临时文件的路径 下面将介绍
                   Streams.copy(item.openStream(), fileItem.getOutputStream(),
                            true);
                } catch (FileUploadIOException e) {
                    throw (FileUploadException) e.getCause();
                } catch (IOException e) {
                    throw new IOFileUploadException(
                            "Processing of " + MULTIPART_FORM_DATA
                            + " request failed. " + e.getMessage(), e);
                }
                if (fileItem instanceof FileItemHeadersSupport) {
                    final FileItemHeaders fih = item.getHeaders();
                    ((FileItemHeadersSupport) fileItem).setHeaders(fih);
                }
                items.add(fileItem);
            }
//返回FileItem的集合（关于FileItem的实现类，大家可以参考DiskFileItem）
            return items;
        } catch (FileUploadIOException e) {
            throw (FileUploadException) e.getCause();
        } catch (IOException e) {
            throw new FileUploadException(e.getMessage(), e);
        }
    }

 

  

  public OutputStream getOutputStream()
        throws IOException {
        if (dfos == null) {
            File outputFile = getTempFile();
            dfos = new DeferredFileOutputStream(sizeThreshold, outputFile);
        }
        return dfos;
    }

    protected File getTempFile() {
      //如果没设置临时目录，就用System.getProperty("java.io.tmpdir")
        if (tempFile == null) {
            File tempDir = repository;
            if (tempDir == null) {
                tempDir = new File(System.getProperty("java.io.tmpdir"));
            }
      //设计临时文件名
            String tempFileName =
                "upload_" + UID + "_" + getUniqueId() + ".tmp";

            tempFile = new File(tempDir, tempFileName);
        }
        return tempFile;
    }

 

 

  public FileItemIterator getItemIterator(RequestContext ctx)
    throws FileUploadException, IOException {
        return new FileItemIteratorImpl(ctx);
    }

 

  FileItemIteratorImpl(RequestContext ctx)
                throws FileUploadException, IOException {
            if (ctx == null) {
                throw new NullPointerException("ctx parameter");
            }

            String contentType = ctx.getContentType();

//这就是为什么需要将请求写成multipart/form-data
//  public static final String MULTIPART = "multipart/"  
            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);
            }

            InputStream input = ctx.getInputStream();

//此处的sizeMax就是我们在action中set进去的值
            if (sizeMax >= 0) {
                int requestSize = ctx.getContentLength();
                if (requestSize == -1) {
                    input = new LimitedInputStream(input, sizeMax) {
                        protected void raiseError(long pSizeMax, long pCount)
                                throws IOException {
                            FileUploadException ex =
                                new SizeLimitExceededException(
                                    "the request was rejected because"   + " its size (" + pCount      + ") exceeds the configured maximum" + " (" + pSizeMax + ")",  pCount, pSizeMax);
                            throw new FileUploadIOException(ex);
                        }
                    };
                } else {
//此处主要是判断上传文件的大小是否超过了设定值
                    if (sizeMax >= 0 && requestSize > sizeMax) {
                        throw new SizeLimitExceededException(
                                "the request was rejected because its size ("
 + requestSize   + ") exceeds the configured maximum ("+ sizeMax + ")", requestSize, sizeMax);
                    }
                }
            }

 

当返回了这个FileItem集合后，我们的代码如下

List<FileItem> items = getUploadFileIteams(request,pushObj,goUrl);

	for (FileItem item : items) {
		File file = new File(realPath);
		item.write(file);
	}

这里就将文件真正写到了服务器上

再最后把item.write这个方法贴下吧，大家就更明白了

public void write(File file) throws Exception {
        if (isInMemory()) {
            FileOutputStream fout = null;
            try {
                fout = new FileOutputStream(file);
                fout.write(get());
            } finally {
                if (fout != null) {
                    fout.close();
                }
            }
        } else {
            File outputFile = getStoreLocation();
            if (outputFile != null) {
                // Save the length of the file
                size = outputFile.length();
              //看到下面的代码，大家就应该明白了吧
                if (!outputFile.renameTo(file)) {
                    BufferedInputStream in = null;
                    BufferedOutputStream out = null;
                    try {
                        in = new BufferedInputStream(
                            new FileInputStream(outputFile));
                        out = new BufferedOutputStream(
                                new FileOutputStream(file));
                        IOUtils.copy(in, out);
                    } finally {
                        if (in != null) {
                            try {
                                in.close();
                            } catch (IOException e) {
                                // ignore
                            }
                        }
                        if (out != null) {
                            try {
                                out.close();
                            } catch (IOException e) {
                                // ignore
                            }
                        }
                    }
                }
            } else {
                /*
                 * For whatever reason we cannot write the
                 * file to disk.
                 */
                throw new FileUploadException(
                    "Cannot write uploaded file to disk!");
            }
        }
    }

 关于临时文件的删除，我们可以考虑2种方式，利用DiskFileItem#delete方法手动删除，也可以用

 <listener>
   <listener-class>org.apache.commons.fileupload.servlet.FileCleanerCleanup</listener-class>
</listener>

 

关于FileCleanerCleanup的执行大家可以看看org.apache.commons.io.FileCleaningTracker的实现

评论

3 楼 momantang 2009-11-13  

mark too

2 楼 jk8341444 2009-09-29  

写的一点思路没有

1 楼 loocao 2009-08-25  

mark...