1.增强型for循环，不可以移除元素。java.util.ConcurrentModificationException
public class Test {
public static void main(String[] args) {
// TODO Auto-generated method stub
List<String> list=new ArrayList<String>();
list.add("1");
list.add("2");
list.add("3");
list.add("4");
list.add("5");
for (String string : list) {
list.remove(string);
}
System.out.println("执行结束");
}
}
2.文件上传的servlet
package com.qfedu.upload;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.util.List;
import java.util.UUID;
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 org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
/**
* Servlet implementation class UploadServlet2
*/
@WebServlet("/upload2")
public class UploadServlet2 extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public UploadServlet2() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
// TODO Auto-generated method stub
// 判断上传的表单的数据类型是不是multipart/form-data
boolean isMultipartForm = ServletFileUpload.isMultipartContent(request);
if (!isMultipartForm) {
throw new RuntimeException("表单格式不正确。");
}
// 常规的file上传逻辑
// 能够创建一个“文件上传对象”的工厂
DiskFileItemFactory factory = new DiskFileItemFactory();
// 文件上传对象
ServletFileUpload fileUpload = new ServletFileUpload(factory);
// 设置字符编码
fileUpload.setHeaderEncoding("utf-8");
// 设置上传文件的大小，不可超过2M
fileUpload.setFileSizeMax(2 * 1024 * 1024);
// 设置整个表单的总大小，不可超过5M
fileUpload.setSizeMax(5 * 1024 * 1024);
try {
// 解析一个请求
// 其实就是按照http报文的格式，把request分解为一个一个的item
// FileItem就是表单项
List<FileItem> fileItems = fileUpload.parseRequest(request);
for (FileItem item : fileItems) {
if (item.isFormField()) {
// 它是一个普通数据项
processFormField(item);
} else {
// 它是一个文件项
processFileUpload(item,response);
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
private void processFormField(FileItem item) {
// 得到名字
String name = item.getFieldName();
String value = "";
try {
value = item.getString("utf-8");
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("name=" + name + "; value=" + value);
}
//在web工程中，WEB-INF目录是受保护的目录。
//如果文件保存在WEB-INF下，浏览器无法访问到，进而所谓的“木马”无法运行。
private void processFileUpload(FileItem item,HttpServletResponse response) {
// 首先得到应用（网站）目录，用于保存文件
//String storeDirectory = getServletContext().getRealPath("/WEB-INF/upload");
String storeDirectory = getServletContext().getRealPath("/upload");
// 创建文件的目录对象
File realDirectory = new File(storeDirectory);
if (!realDirectory.exists()) {
realDirectory.mkdirs();
}
// 怎么保存？
// 读一点写一点
InputStream in = null;
FileOutputStream fos = null;
try {
// 拿到文件的读取流
in = item.getInputStream();
// 拿到文件名
String fileName = item.getName();
//不同浏览器文件名格式不一致
//ie:D:\temp\temp.jpg
//火狐谷歌：temp.jpg
fileName=fileName.substring(fileName.lastIndexOf(File.separator)+1);
//假如asdf.jsp
//是否以.jsp结尾
//p.jpg
//alsdjkfl.jspalksjdflkaj.jsp
if(fileName.lastIndexOf(".jsp")==fileName.length()-4) {
response.getWriter().print("您的ip地址已经记录，请勿尝试非法操作，本网站保留追责权利。");
throw new RuntimeException("您的ip地址已经记录，请勿尝试非法操作，本网站保留追责权利。");
}
//至此，文件不是以.jsp结尾的了
//许多用户上传文件，文件名相同会被覆盖。
//UUID，标识唯一的字符串
//使用uuid作为文件名的前缀
fileName=UUID.randomUUID().toString()+"_"+fileName;
//获取子目录
String childDirectory=getChildDirectory(realDirectory, fileName);
File file = new File(realDirectory, childDirectory+File.separator+fileName);
fos = new FileOutputStream(file);
byte[] arr = new byte[1024];
int len = 0;
for (; (len = in.read(arr)) != -1;) {
fos.write(arr, 0, len);
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
try {
if (in != null) {
in.close();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
try {
if (fos != null) {
fos.close();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
//创建两级子目录，每一级16个，并且使用文件名的hashcode将文件分散在每一个目录中
private String getChildDirectory(File realDirectory,String fileName) {
int hashCode=fileName.hashCode();
//code的形式是1ef39b
String code=Integer.toHexString(hashCode);
//利用hashcode的十六进制的前两位，作为两级子目录的名字
String childDirectory=code.charAt(0)+File.separator+code.charAt(1);
//子目录如同：upload/a/c/ upload/1/a/
File dir=new File(realDirectory,childDirectory);
if(!dir.exists()) {
dir.mkdirs();
}
return childDirectory;
}
/**
* @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);
}
}
3.html
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> <form action="upload2" method="post" enctype="multipart/form-data"> <input type="file" name="icon"/> <input type="text" name="username"/> <input type="submit" value="提交"/> </form> </body> </html>
4.icon.html读取文件
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> </head> <body> <img id="img" width="200px" height="120px" src="upload/b/b/639bddf7-d0d9-47a7-9c58-f921839b140b_qflogo.jpg"/> </body> </html>