上传文件

1.导包（commons-fileupload-1.2.2.jar和commons-io-2.3.jar）
2.写一个jsp页面 uploads.jsp
  //method='POST'必须是post enctype='multipart/form-data'必须是multipart/form-data 
  <form method='POST' action='<%=application.getContextPath() %>/upload' enctype='multipart/form-data'>
		<input type='file' name='file_a'><br> 
		<input type='file' name='file_b'><br> 
		<input type='submit'>
	</form>
3.映射 web.xml
<servlet>
  	<servlet-name>fileUploads</servlet-name>
  	<servlet-class>handler.FileUploads</servlet-class>
  </servlet>
  <servlet-mapping>
  	<servlet-name>fileUploads</servlet-name>
  	<url-pattern>/upload</url-pattern>
  </servlet-mapping>
4.计算sha1码  Md5.java
package handler;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class Md5 {
	public static String sha1(byte[] data) {
		try {
			byte[] sha1data = MessageDigest.getInstance("sha1").digest(data);
			return new String(byteToHex(sha1data));
		} catch (NoSuchAlgorithmException e) {
			throw new RuntimeException(e);
		}
	}

	public static byte[] byteToHex(byte[] bytes) {
		final String HEX_CHAR = "0123456789abcdef";
		byte[] r = new byte[bytes.length * 2];
		for (int i = 0; i < bytes.length; ++i) {
			r[i * 2] = (byte) HEX_CHAR.charAt((bytes[i] >>> 4) & 15);
			r[i * 2 + 1] = (byte) HEX_CHAR.charAt(bytes[i] & 15);
		}
		return r;
	}

	public static void main(String[] args) {
		System.out.println(sha1("password".getBytes()));
	}
}
5.servlet类 FileUploads.java
package handler;

import java.io.File;
import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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

public class FileUploads extends HttpServlet{

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		req.setCharacterEncoding("utf-8");
		
		 // 初始化和配置
		ServletFileUpload upload = new ServletFileUpload(new DiskFileItemFactory());
		upload.setFileSizeMax(1024*1024);//设置单个文件大小
		upload.setSizeMax(1024*1024*8);//设置全部文件大小的总和
       
		try {
			 // 解析请求, 得到文件列表
			List<FileItem> items = upload.parseRequest(req);
			for (FileItem item : items) {
				if(item.getName().isEmpty()){
					continue;
				}
				System.out.println("用户上传的文件名："+item.getName());
				// 确定文件该保存在哪里
				System.out.println("getServletContext().getRealPath ==>"+getServletContext().getRealPath("uploads"));
                String sha1=Md5.sha1(item.get());
				System.out.println("sha1---"+sha1);
				File target = new File(getServletContext().getRealPath("uploads")
	                    + File.separatorChar + sha1);
if(target.exists()){
					System.out.println("file exists");
					continue;
				}
				// 保存文件
				System.out.println("保存位置："+target.getAbsolutePath());
				item.write(target);
			}
		} catch (FileUploadException e) {
			throw new IOException(e);
		}catch (Exception e) {
			throw new IOException(e);
		}
	}
}