关于读取文件

Question

一时半伙没法讲,文件操作这块是java中比较难的地方,涉及到缓存与流处理,

Answer 1

就是bufferreader inputstreanreader 来回套用

Answer 2

这里是struts开源项目中的一个读取上传文件的类，可以参考一下：package org.apache.struts.webapp.upload;
import java.io.ByteArrayOutputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.upload.FormFile;/**
 * This class takes the UploadForm and retrieves the text value
 * and file attributes and puts them in the request for the display.jsp
 * page to display them
 *
 * @author Mike Schachter
 * @version $Revision: 1.8 $ $Date: 2003/02/28 02:18:23 $
 */
public class UploadAction extends Action
{
    public ActionForward execute(ActionMapping mapping,
                                 ActionForm form,
                                 HttpServletRequest request,
                                 HttpServletResponse response)
        throws Exception {        if (form instanceof UploadForm) {            //this line is here for when the input page is upload-utf8.jsp,
            //it sets the correct character encoding for the response
            String encoding = request.getCharacterEncoding();
            if ((encoding != null) && (encoding.equalsIgnoreCase("utf-8")))
            {
                response.setContentType("text/html; charset=utf-8");
            }            UploadForm theForm = (UploadForm) form;            //retrieve the text data
            String text = theForm.getTheText();            //retrieve the query string value
            String queryValue = theForm.getQueryParam();            //retrieve the file representation
            FormFile file = theForm.getTheFile();            //retrieve the file name
            String fileName= file.getFileName();            //retrieve the content type
            String contentType = file.getContentType();            boolean writeFile = theForm.getWriteFile();            //retrieve the file size
            String size = (file.getFileSize() + " bytes");            String data = null;            try {
                //retrieve the file data
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                InputStream stream = file.getInputStream();
                if (!writeFile) {
                    //only write files out that are less than 1MB
                    if (file.getFileSize() < (4*1024000)) {                        byte[] buffer = new byte[8192];
                        int bytesRead = 0;
                        while ((bytesRead = stream.read(buffer, 0, 8192)) != -1) {
                            baos.write(buffer, 0, bytesRead);
                        }
                        data = new String(baos.toByteArray());
                    }
                    else {
                        data = new String("The file is greater than 4MB, " +
                                " and has not been written to stream." +
                                " File Size: " + file.getFileSize() + " bytes. This is a" +
                                " limitation of this particular web application, hard-coded" +
                                " in org.apache.struts.webapp.upload.UploadAction");
                    }
                }
                else {
                    //write the file to the file specified
                    OutputStream bos = new FileOutputStream(theForm.getFilePath());
                    int bytesRead = 0;
                    byte[] buffer = new byte[8192];
                    while ((bytesRead = stream.read(buffer, 0, 8192)) != -1) {
                        bos.write(buffer, 0, bytesRead);
                    }
                    bos.close();
                    data = "The file has been written to \"" + theForm.getFilePath() + "\"";
                }
                //close the stream
                stream.close();
            }
            catch (FileNotFoundException fnfe) {
                return null;
            }
            catch (IOException ioe) {
                return null;
            }            //place the data into the request for retrieval from display.jsp
            request.setAttribute("text", text);
            request.setAttribute("queryValue", queryValue);
            request.setAttribute("fileName", fileName);
            request.setAttribute("contentType", contentType);
            request.setAttribute("size", size);
            request.setAttribute("data", data);            //destroy the temporary file created
            file.destroy();            //return a forward to display.jsp
            return mapping.findForward("display");
        }        //this shouldn't happen in this example
        return null;
    }
}

Answer 3

既然提交上来了就不用确定位置了 ，行处理 用BufferedReader

Answer 4

下面这几句就是有关读取上传文件的语句：
//retrieve the file representation 
//取得上传文件的句柄
FormFile file = theForm.getTheFile();//retrieve the file data
//读取文件流
ByteArrayOutputStream baos = new ByteArrayOutputStream();
InputStream stream = file.getInputStream();while ((bytesRead = stream.read(buffer, 0, 8192)) != -1) 
{
 ... ...
 }

Answer 5

sorry,下面这句不要：
ByteArrayOutputStream baos = new ByteArrayOutputStream();这是用来把文件输出到本地的。