React+ajax+java 上传图片并预览

  在此以前有在网上找ajax上传图片的资料,大部分的人写得都是用jQuery,可是在这里用JQuery就大才小用了,所以自己就协调写了,先上图。

  图片 1

  由上图,首先点击上边的挑选文件,在挑选图片之后,将会活动上传图片到服务器,并且重回图片名字和图表在服务器的路子,然后在页面彰显文件名字和图片。

  源码:http://download.csdn.net/detail/nsguf/9851189

  React中:

 1 import React from 'react';
 2 import Http from './http'
 3 
 4 const URL = 'http://localhost:8080/fileuploadExample/UploadServlet';
 5 
 6 export default class App extends React.Component {
 7     constructor(props) {
 8         super(props);
 9 
10         this.state = {
11             uploadedFile: "",
12             uploadedFileGetUrl: ''
13         };
14     }
15 
16     error() {
17         alert('error')
18     }
19 
20     callback(result) {
21         this.setState({
22             uploadedFile: result.uploadedFile,
23             uploadedFileGetUrl: result.uploadedFileGetUrl
24         });
25     }
26 
27     handleImageUpload(e) {
28         e.preventDefault()
29         let file = e.target
30         Http.post(URL, file, this.callback.bind(this), this.error)
31     }
32 
33     render() {
34         return (
35             <div>
36                 <input type="file" onChange={this.handleImageUpload.bind(this)}/>
37                 <div>
38                     {this.state.uploadedFileGetUrl === '' ? null :
39                         <div>
40                             <p>{this.state.uploadedFile}</p>
41                             <img src={this.state.uploadedFileGetUrl} alt="你选择的图片"/>
42                         </div>}
43                 </div>
44             </div>
45         )
46     }
47 }

  自己包装的Ajax代码:

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() {//超时设置
            error();
        }, 10000);
        var xhr = new XMLHttpRequest();
        xhr.open('post', url);
        xhr.onreadystatechange = function() {
            if (xhr.readyState === 4) {
                clearTimeout(timeout);//清除超时
                if (xhr.status === 200){
                    //alert(xhr.responseText);
                    callback(JSON.parse(xhr.responseText));//调用回调函数
                } else {
                    error();
                }
                xhr = null;// 删除对象,防止内存溢出
            }
        };
        xhr.onerror = function() {//如果产生了错误
            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

  在java后台上传图片方面,网上有许多例子都足以用,我借鉴的是http://blog.csdn.net/thc1987/article/details/15341201这篇,有兴趣可以看一下:

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;

    // 保存文件的目录
    private static String PATH_FOLDER = "/";
    // 存放临时文件的目录
    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();
        // 初始化路径
        // 保存文件的目录
        PATH_FOLDER = servletCtx.getRealPath("/upload");
        // 存放临时文件的目录,存放xxx.tmp文件的目录
        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"); // 设置编码
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");
        // 获得磁盘文件条目工厂
        DiskFileItemFactory factory = new DiskFileItemFactory();

        // 如果没以下两行设置的话,上传大的 文件 会占用 很多内存,
        // 设置暂时存放的 存储室 , 这个存储室,可以和 最终存储文件 的目录不同
        /**
         * 原理 它是先存到 暂时存储室,然后在真正写到 对应目录的硬盘上, 按理来说 当上传一个文件时,其实是上传了两份,第一个是以 .tem
         * 格式的 然后再将其真正写到 对应目录的硬盘上
         */
        factory.setRepository(new File(TEMP_FOLDER));
        // 设置 缓存的大小,当上传文件的容量超过该缓存时,直接放到 暂时存储室
        factory.setSizeThreshold(1024 * 1024);

        // 高水平的API文件上传处理
        ServletFileUpload upload = new ServletFileUpload(factory);

        try {
            // 提交上来的信息都在这个list里面
            // 这意味着可以上传多个文件
            // 请自行组织代码
            List<FileItem> list = upload.parseRequest(request);
            // 获取上传的文件
            FileItem item = getUploadFileItem(list);
            // 获取文件名
            String filename = getUploadFileName(item);
            // 保存后的文件名
            String saveName = new Date().getTime()
                    + filename.substring(filename.lastIndexOf("."));
            // 保存后图片的浏览器访问路径
            String picUrl = request.getScheme() + "://"
                    + request.getServerName() + ":" + request.getServerPort()
                    + request.getContextPath() + "/upload/" + saveName;

            System.out.println("存放目录:" + PATH_FOLDER);
            System.out.println("文件名:" + filename);
            System.out.println("浏览器访问路径:" + picUrl);

            // 真正写到磁盘上
            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) {
        // 获取路径名
        String value = item.getName();
        System.out.println(value + ":value");
        // 索引到最后一个反斜杠
        int start = value.lastIndexOf("/");
        // 截取 上传文件的 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);
    }

}

以上java代码这里修改了这几点:

  1、插入response.setHeader(“Access-Control-Allow-Origin”,”http://localhost:3000“);
    response.setHeader(“Access-Control-Allow-Credentials”, “true”);

  这两行代码,举行跨域,当然,这些也许不安全

  2、

  JSONObject result = new JSONObject();
  result.put(“uploadedFile”, filename);

  result.put(“uploadedFileGetUrl”, picUrl);
  writer.write(result.toString());

  在此处,页面和服务器之间使用json数据传输的

 本人第一次发布博文,请批评指正~~~

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