java如何实现文件上传和下载功能？这个问题可能是我们日常学习或工作经常见到的。希望通过这个问题能让你收获颇深。下面是小编给大家带来的参考内容，让我们一起来看看吧！
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需要导入的jar包
运行截图
文件上传截图
文件下载截图
上传文件代码servlet
@WebServlet(name = "UploadServlet",value = "/upload")
@MultipartConfig(maxFileSize = 1024*1024*5,maxRequestSize = 1024*1024*20) //1 添加MultipartConfig注解
public class UploadServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//存放文件的目录
String realPath = request.getServletContext().getRealPath("/WEB-INF/upload");
File dir=new File(realPath);
if(!dir.exists()){
dir.mkdirs();
}
List allowExts=new ArrayList();
allowExts.add("jpg");
allowExts.add("png");
allowExts.add("gif");
//1乱码
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
//2使用getParts()获取数据
Collection parts = request.getParts();
//3遍历
PrintWriter out = response.getWriter();
if(parts!=null&&parts.size()>0){
for (Part part : parts) {
//判断表单元素是普通字段，还是文件
String submittedFileName = part.getSubmittedFileName();
if(submittedFileName==null){//普通字段
String name = part.getName();
String value = request.getParameter(name);
System.out.println(name+"..."+value);
}else{//文件
//判断文件是否为""
if(submittedFileName.equals("")){
continue;
}
//System.out.println(submittedFileName);
//从请求头中获取文件
String dis = part.getHeader("content-disposition");
String filename=dis.substring(dis.lastIndexOf("filename=")+10, dis.length()-1);
filename=filename.substring(filename.lastIndexOf("\\")+1);
System.out.println(filename);
//获取文件名的后缀
String ext=filename.substring(filename.lastIndexOf(".")+1);
if(!allowExts.contains(ext)){
out.println(filename+"不符合上传文件类型要求...");
continue;
}
//把文件保存
//1创建新的文件名
String newFileName = UploadUtils.makeNewFileName(filename);
//2创建新的路径
String newPath = UploadUtils.makeNewPath(realPath, filename);
part.write(newPath+File.separator+newFileName);
//删除part
part.delete();
out.println("上传成功:"+filename);
}
}
}
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request,response);
}
} 每个属性表示的内容
文件下载代码servlet
@WebServlet(name = "DownLoadServlet",value = "/download")
public class DownLoadServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//乱码
request.setCharacterEncoding("utf-8");
//获取文件名
String uuidFilename = request.getParameter("filename");//d578be74fd864ac2a879d77b07f13793_backg.jpg
//去掉uuid
String filename=uuidFilename.substring(uuidFilename.indexOf("_")+1);
//存放文件的根路径
String realPath = request.getServletContext().getRealPath("/WEB-INF/upload");
//获取真正目录
String path = UploadUtils.makeNewPath(realPath, filename);
File file=new File(path+ File.separator+uuidFilename);
if(file.exists()){
response.setHeader("content-disposition", "attachment;filename="+ URLEncoder.encode(filename, "utf-8"));
ServletOutputStream os = response.getOutputStream();
FileInputStream fis=new FileInputStream(file);
byte[] buf=new byte[1024*4];
int len=0;
while((len=fis.read(buf))!=-1){
os.write(buf,0,len);
}
}else{
response.setContentType("text/html;charset=utf-8");
response.getWriter().write("文件不存在...");
}
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
}每个属性表示的内容
读取下载文件servlet
@WebServlet(name = "ListFileServlet",value = "/listfile")
public class ListFileServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
//1读取可以被下载的文件
String realPath = request.getServletContext().getRealPath("/WEB-INF/upload");
HashMap map=new HashMap<>();
UploadUtils.listFile(new File(realPath),map);
//2放入域中
request.setAttribute("map", map);
//3转发
request.getRequestDispatcher("/list.jsp").forward(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doPost(request, response);
}
} 工具类servlet
public class UploadUtils {
public static void main(String[] args) {
String s = makeNewFileName("aaa.jpg");
System.out.println(s);
}
/**
* 根据原始文件名产生一个新的文件名
* @param filename
* @return
*/
public static String makeNewFileName(String filename){
//UUID 统一唯一标识码
String uuid = UUID.randomUUID().toString().replace("-", "");//默认32位的16进制
return uuid+"_"+filename;
}
/**
* 创建新的路径
* @param path
* @param filename
* @return
*/
public static String makeNewPath(String path,String filename){
int num = filename.hashCode();//01101011001011011111111111 1111 0101 0101
int path2=num&0xf;
int path3=(num>>4)&0xf;
String newPath=path+ File.separator+path2+File.separator+path3;
File dir=new File(newPath);
if(!dir.exists()){
dir.mkdirs();
}
return newPath;
}
//遍历可以被下载的文件
public static void listFile(File dir,HashMap map){
File[] files = dir.listFiles();
if(files!=null&&files.length>0){
for (File file : files) {
if(file.isDirectory()){
listFile(file, map);
}else{
//文件
String uuidFilename=file.getName();
String filename=uuidFilename.substring(uuidFilename.indexOf("_")+1);
map.put(uuidFilename,filename);
}
}
}
}
} 感谢各位的阅读！看完上述内容，你们对java如何实现文件上传和下载功能大概了解了吗？希望文章内容对大家有所帮助。如果想了解更多相关文章内容，欢迎关注创新互联行业资讯频道。