前言

commons-fileupload虽然我经常会在项目里用的，它有非常强大的文件上传功能，虽然经常用，却不曾了解过其源码的实现，为了让自己更加牛B，更好的掌握文件上传的原理和具体实现方式，我开始了长达一个月的解析该框架源码的工作，总算将框架的实现原理给摸清。是时候写一系列博客来装B,comons-fileupload的版本是1.4

第一章简介

第一章的我并不是马上讲起原理，而是直接我的用例展现出来，我打算通过该用例去解析其原理。

用例

只是一个普通的JavaWeb项目，代码的实现都在FileUploadServlet里

目录结构截图

项目目录结构.png

pom.xml

  <dependency>
          <groupId>commons-fileupload</groupId>
          <artifactId>commons-fileupload</artifactId>
          <version>1.4</version>
      </dependency>

FileUploadServlet

package bin.study;

import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.util.Iterator;
import java.util.List;

/**
 * 实现文件上传的Servlet
 * @author Administrator
 *
 */
public class FileUploadServlet extends HttpServlet {


    //上传路径
    private File uploadPath;


    //当文件过大时，需要设置一个临时路径
    private File tempPath;


    public void doPost(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {

        DiskFileItemFactory factory = new DiskFileItemFactory();
        // 内存存储的最大值
        factory.setSizeThreshold(4096);

        factory.setRepository(tempPath);

        ServletFileUpload upload = new ServletFileUpload(factory);
        //设置文件上传大小
        upload.setSizeMax(1000000 * 20);
        try {
            List fileItems = upload.parseRequest(req);
            String itemNo = "";
            for (Iterator iter = fileItems.iterator(); iter.hasNext(); ) {
                FileItem item = (FileItem) iter.next();

                //是普通的表单输入域
                if (item.isFormField()) {
                    if ("itemNo".equals(item.getFieldName())) {
                        itemNo = item.getString();
                    }
                }
                //是否为input="type"输入域
                if (!item.isFormField()) {
                    String fileName = item.getName();
                    long size = item.getSize();
                    if ((fileName == null || fileName.equals("")) && size == 0) {
                        continue;
                    }
                    //截取字符串 如：C:\WINDOWS\Debug\PASSWD.LOG
                    fileName = fileName.substring(fileName.lastIndexOf("\\") + 1, fileName.length());
                    //item.write(new File(uploadPath + itemNo + ".gif"));
                    item.write(new File(uploadPath, itemNo + ".gif"));
                }
            }
            //重定向页面
            res.sendRedirect(req.getContextPath() + "/servlet/item/SearchItemServlet");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * 初始化方法，设定目录
     */
    public void init() throws ServletException {
        uploadPath = new File(getServletContext().getRealPath("upload"));
        //System.out.println("uploadPath=====" + uploadPath);
        //如果目录不存在
        if (!uploadPath.exists()) {
            //创建目录
            uploadPath.mkdir();
        }

        //临时目录
        tempPath = new File(getServletContext().getRealPath("temp"));
        if (!tempPath.exists()) {
            tempPath.mkdir();
        }
    }
}

web.xml

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
  <servlet>
    <servlet-name>fileUploadServlet</servlet-name>
    <servlet-class>bin.study.FileUploadServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>fileUploadServlet</servlet-name>
    <url-pattern>/fileUploadServlet</url-pattern>
  </servlet-mapping>
</web-app>

commons-fileupload框架源码解析(一)--实例