import React from 'react';import Http from './http'const URL = 'http://localhost:8080/fileuploadExample/UploadServlet';export default class App extends React.Component { constructor(props) {  super(props);  this.state = {   uploadedFile: "",   uploadedFileGetUrl: ''  }; } error() {  alert('error') } callback(result) {  this.setState({   uploadedFile: result.uploadedFile,   uploadedFileGetUrl: result.uploadedFileGetUrl  }); } handleImageUpload(e) {  e.preventDefault()  let file = e.target  Http.post(URL, file, this.callback.bind(this), this.error) } render() {  return (   <div>    <input type="file" onChange={this.handleImageUpload.bind(this)}/>    <div>     {this.state.uploadedFileGetUrl === '' ? null :      <div>       <p>{this.state.uploadedFile}</p>       <img src={this.state.uploadedFileGetUrl} alt="你選擇的圖片"/>      </div>}    </div>   </div>  ) }}

var Http = (function() { var http = {}; if (typeof window.XMLHttpRequest === "undefined") {  window.XMLHttpRequest = function() {   // 如果是i5就用Microsoft，其他就用Msxml2   return new window.ActiveXObject(navigator.userAgent     .indexOf("MSIE 5") >= 0 ? "Microsoft.XMLHTTP"     : "Msxml2.XMLHTTP");  }; } http.post = function(url, data, callback, error) {  if (typeof data === "function") {//data可以不穿值   callback = data;   data = null;  }  var timeout = setTimeout(function() {//超時設置   error();  }, 10000);  var xhr = new XMLHttpRequest();  xhr.open('post', url);  xhr.onreadystatechange = function() {   if (xhr.readyState === 4) {    clearTimeout(timeout);//清除超時    if (xhr.status === 200){     //alert(xhr.responseText);     callback(JSON.parse(xhr.responseText));//調用回調函數    } else {     error();    }    xhr = null;// 刪除對象,防止內存溢出   }  };  xhr.onerror = function() {//如果產生了錯誤   clearTimeout(timeout);   error();  };  xhr.send(http.formDataCode(data)); }; http.formDataCode = function(data) {  var fd = new FormData();  if (!data) {   return null;  }  for ( var key in data) {   if(data.files){    var file=data.files[0];    fd.append("image", file);   }else{    fd.append(key, data[key]);   }  }  return fd; } return http;})();export default Http

package com.example;import java.io.File;import java.io.IOException;import java.io.PrintWriter;import java.util.Date;import java.util.List;import javax.servlet.ServletConfig;import javax.servlet.ServletContext;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 net.sf.json.JSONObject;import org.apache.commons.fileupload.FileItem;import org.apache.commons.fileupload.disk.DiskFileItemFactory;import org.apache.commons.fileupload.servlet.ServletFileUpload;/** * Servlet implementation class UploadServlet */@WebServlet("/UploadServlet")public class UploadServlet extends HttpServlet { private static final long serialVersionUID = 1L; // 保存文件的目錄 private static String PATH_FOLDER = "/"; // 存放臨時文件的目錄 private static String TEMP_FOLDER = "/"; /**  * @see HttpServlet#HttpServlet()  */ public UploadServlet() {  super();  // TODO Auto-generated constructor stub } @Override public void init(ServletConfig config) throws ServletException {  // TODO Auto-generated method stub  super.init();  ServletContext servletCtx = config.getServletContext();  // 初始化路徑  // 保存文件的目錄  PATH_FOLDER = servletCtx.getRealPath("/upload");  // 存放臨時文件的目錄,存放xxx.tmp文件的目錄  TEMP_FOLDER = servletCtx.getRealPath("/uploadTemp"); } /**  * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse  *  response)  */ protected void doGet(HttpServletRequest request,   HttpServletResponse response) throws ServletException, IOException {  response.setHeader("Access-Control-Allow-Origin",    "http://localhost:3000");  response.setHeader("Access-Control-Allow-Credentials", "true");  request.setCharacterEncoding("utf-8"); // 設置編碼  response.setCharacterEncoding("utf-8");  response.setContentType("text/html;charset=UTF-8");  // 獲得磁盤文件條目工廠  DiskFileItemFactory factory = new DiskFileItemFactory();  // 如果沒以下兩行設置的話，上傳大的 文件 會占用 很多內存，  // 設置暫時存放的 存儲室 , 這個存儲室，可以和 最終存儲文件 的目錄不同  /**   * 原理 它是先存到 暫時存儲室，然后在真正寫到 對應目錄的硬盤上， 按理來說 當上傳一個文件時，其實是上傳了兩份，第一個是以 .tem   * 格式的 然后再將其真正寫到 對應目錄的硬盤上   */  factory.setRepository(new File(TEMP_FOLDER));  // 設置 緩存的大小，當上傳文件的容量超過該緩存時，直接放到 暫時存儲室  factory.setSizeThreshold(1024 * 1024);  // 高水平的API文件上傳處理  ServletFileUpload upload = new ServletFileUpload(factory);  try {   // 提交上來的信息都在這個list里面   // 這意味著可以上傳多個文件   // 請自行組織代碼   List<FileItem> list = upload.parseRequest(request);   // 獲取上傳的文件   FileItem item = getUploadFileItem(list);   // 獲取文件名   String filename = getUploadFileName(item);   // 保存后的文件名   String saveName = new Date().getTime()     + filename.substring(filename.lastIndexOf("."));   // 保存后圖片的瀏覽器訪問路徑   String picUrl = request.getScheme() + "://"     + request.getServerName() + ":" + request.getServerPort()     + request.getContextPath() + "/upload/" + saveName;   System.out.println("存放目錄:" + PATH_FOLDER);   System.out.println("文件名:" + filename);   System.out.println("瀏覽器訪問路徑:" + picUrl);   // 真正寫到磁盤上   item.write(new File(PATH_FOLDER, saveName)); // 第三方提供的   PrintWriter writer = response.getWriter();   System.out.print("{");   System.out.print("uploadedFile:"+ "/"" + filename + "/"");   System.out.print(",uploadedFileGetUrl:/"" + picUrl + "/"");   System.out.print("}");      JSONObject result = new JSONObject();   result.put("uploadedFile", filename);   result.put("uploadedFileGetUrl", picUrl);   writer.write(result.toString());   writer.close();  } catch (Exception e) {   e.printStackTrace();   /*    * PrintWriter writer = response.getWriter(); writer.print("{");    * writer.print("error:"+e.toString()); writer.print("}");    * writer.close();    */  } } private FileItem getUploadFileItem(List<FileItem> list) {  for (FileItem fileItem : list) {   if (!fileItem.isFormField()) {    return fileItem;   }  }  return null; } private String getUploadFileName(FileItem item) {  // 獲取路徑名  String value = item.getName();  System.out.println(value + ":value");  // 索引到最后一個反斜杠  int start = value.lastIndexOf("/");  // 截取 上傳文件的 字符串名字，加1是 去掉反斜杠，  String filename = value.substring(start + 1);  return filename; } /**  * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse  *  response)  */ protected void doPost(HttpServletRequest request,   HttpServletResponse response) throws ServletException, IOException {  doGet(request, response); }}

response.setHeader("Access-Control-Allow-Origin","http://localhost:3000");response.setHeader("Access-Control-Allow-Credentials", "true");

JSONObject result = new JSONObject();result.put("uploadedFile", filename);result.put("uploadedFileGetUrl", picUrl);writer.write(result.toString());