上传文件

a.引入2个jar
apache: commons-fileupload.jar组件
commons-fileupload.jar依赖 commons-io.jar

b.
代码：
前台jsp：

表单提交方式必须为post
在表单中必须增加一个属性 entype=“multipart/form-data”

后台servlet：

注意的问题：
上传的目录 upload ：
1.如果修改代码，则在tomcat重新启动时会被删除
原因：当修改代码的时候,tomcat会重新编译一份class 并且重新部署（重新创建各种目录）

2.如果不修改代码，则不会删除
原因：没有修改代码，class仍然是之前的class

因此，为了防止上传目录丢失： a.虚拟路径 b.直接更换上传目录到非tomcat目录

限制上传：
类型、
大小
注意对文件的限制条件写再parseRequest之前

下载文件

不需要依赖任何jar
a.请求（地址a form），请求Servlet
b.Servlet通过文件的地址将文件转为输入流读到Servlet中
c.通过输出流将刚才已经转为输入流的文件输出给用户
注意：下载文件需要设置2个响应头：
response.addHeader(“content-Type”,“application/octet-stream” );//MIME类型:二进制文件（任意文件）
response.addHeader(“content-Disposition”,“attachement;filename=”+fileName );//fileName包含了文件后缀：abc.txt
在这里插入图片描述

代码

UploadServlet

package org.student.servlet;

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

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;

/**
 * Servlet implementation class UploadServet
 */
@WebServlet(name = "UploadServlet" ,value = "/UploadServlet")
public class UploadServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;

	public UploadServlet() {
		super();
	}

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		request.setCharacterEncoding("utf-8");
		response.setCharacterEncoding("utf-8");
		response.setContentType("text/html; charset=UTF-8");
		// 上传
		// request.getParameter("sname")
		try {
			boolean isMultipart = ServletFileUpload.isMultipartContent(request);
			if (isMultipart) {// 判断前台的form是否有 mutipart属性
//				FileItemFactory factory = new DiskFileItemFactory();
				DiskFileItemFactory factory = new DiskFileItemFactory();
				
				ServletFileUpload upload = new ServletFileUpload(factory);
				
				//设置上传文件时 用到的临时文件的大小DiskFileItemFactory
				factory.setSizeThreshold(10240*10);//设置临时的缓冲文件大小为10
				factory.setRepository(new File("D:\\Users\\MACROSS\\IdeaProjects\\JavaWeb\\web\\uploadtemp"));//设置临时文件的目录
				//控制上传单个文件的大小  20KB ServletFileUpload
				upload.setSizeMax(1024*1024*10);//字节B


				// 通过parseRequest解析form中的所有请求字段，并保存到 items集合中（即前台传递的sno sname
				// spicture此时就保存在了items中）
				List items = upload.parseRequest(request);
				// 遍历items中的数据（item=sno sname spicture）
				Iterator iter = items.iterator();
				while (iter.hasNext()) {
					FileItem item =(FileItem) iter.next();
					String itemName = item.getFieldName();
					int sno = -1;
					String sname = null;
					// 判断前台字段 是普通form表单字段(sno sname)，还是文件字段

					// request.getParameter() -- iter.getString()
					if (item.isFormField()) {
						if (itemName.equals("sno")) {// 根据name属性 判断item是sno sname 还是spicture?
							sno = Integer.parseInt(item.getString("UTF-8"));
						} else if (itemName.equals("sname")) {
							sname = item.getString("UTF-8");
						} else {
							System.out.println("其他字段xxx.....");
						}
					} else {// spicture 123
							// 文件 上传
							// 文件名 getFieldName是获取 普通表单字段的Name值
							// getName()是获取 文件名
						String fileName = item.getName();//a.txt   a.docx   a.png
						String ext = fileName.substring(  fileName.indexOf(".")+1 ) ;
						if(!(ext.equals("png") || ext.equals("gif") ||ext.equals("jpg"))) {
							System.out.println("图片类型有误！格式只能是 png gif  jpg");
							return ;//终止
						}
						// 获取文件内容 并上传
						// 定义文件路径：指定上传的位置(服务器路径)
						// 获取服务器路径D:\\study\\apache-tomcat-8.5.30\\wtpwebapps\\UpAndDown\\upload
						String path =request.getSession().getServletContext().getRealPath("/uploaded") ;
//						String path = "D:\\study\\upload";
						System.out.println(path);
						File file = new File(path, fileName);
						
					

						item.write(file);// 上传
						System.out.println(fileName + "上传成功！");
						return;
					}
				}

			}

		}
		catch (FileUploadBase.SizeLimitExceededException e) {//SizeLimitExceededException是FileUploadException的一个子类
			System.out.println("上传文件大小超过限制！最大20KB");
		}
		catch (FileUploadException e) 
		{
			e.printStackTrace();
			
		}
		
		// 解析请求
		catch (Exception e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}

	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
	 *      response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

DownLoadServlet

package org.student.servlet;

import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.net.URLEncoder;



/**
 * Servlet implementation class DownLoadServlet
 */
@WebServlet(name = "DownLoadServlet",value = "/DownLoadServlet")
public class DownLoadServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public DownLoadServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        String filename = request.getParameter("filename");
        response.addHeader("content-Type", "application/octet-stream");

        String agent = request.getHeader("User-Agent");

        if(agent.toLowerCase().indexOf("chrome")>0)
        {
            response.addHeader("content-Disposition", "attachment;filename="+new String(filename.getBytes("UTF-8"), "ISO8859-1"));
        }
        else
        {
            response.addHeader("content-Disposition", "attachment;filename="+URLEncoder.encode(filename, "UTF-8"));
        }
        InputStream in = getServletContext().getResourceAsStream("/download/"+filename);
        ServletOutputStream out = response.getOutputStream();
        byte[] bs=new byte[1024];
        int len=-1;
        while((len=in.read(bs))!=-1)
        {
            out.write(bs,0,len);
        }
        out.close();
        in.close();
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

ervletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}

JavaWeb开发技术学习笔记（七）——上传与下载

上传文件

下载文件

代码

UploadServlet

DownLoadServlet

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