js上传文件 java后台接收文件

1、前端向后台传送文件的过程其实就是，前端将文件流传给后台，后台接收文件流，然后将其写到后台服务器上。处理文件时，后台程序只需要读取服务器上的文件即可。

2、需要引入两个jar包：commons-fileupload-1.3.1.jar和commons-io-2.4.jar。

html代码：

<div class="input-chunk">
<div>输入文件：</div>
<input type="file" value="选择文件" id="upload-file">
<br>
<a id="start-upload" href="javascript:void(0);" onclick="uploadFile();">开始上传</a>
</div>

js代码：

function uploadFile(){
var fileObj = document.getElementById("upload-file").files[0]; // 获取文件对象
var FileController = "entityServlet1"; // 接收上传文件的后台地址

if(fileObj){
alert(fileObj);
// FormData 对象
var form = new FormData();
form.append("file", fileObj);// 文件对象

// XMLHttpRequest 对象
var xhr = new XMLHttpRequest();
xhr.open("post", FileController, true);
xhr.onload = function () {
alert(xhr.responseText);
};
xhr.send(form);

}else{
alert("未选择文件");
}
}

Java Servlet代码：

import java.io.File;
import java.io.IOException;
import java.util.Iterator;
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.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;

public class EntityServlet1 extends HttpServlet {

private static final long serialVersionUID = 1L;
private String uploadPath = "D:\\temp"; // 上传文件的目录
File tempPathFile;

// 重写doPost方法，处理事件识别请求
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
try {
// Create a factory for disk-based file items
DiskFileItemFactory factory = new DiskFileItemFactory();

// Set factory constraints
factory.setSizeThreshold(4096); // 设置缓冲区大小，这里是4kb
factory.setRepository(tempPathFile);// 设置缓冲区目录

// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);

// Set overall request size constraint
upload.setSizeMax(4194304); // 设置最大文件尺寸，这里是4MB

List<FileItem> items = upload.parseRequest(request);// 得到所有的文件
Iterator<FileItem> i = items.iterator();
while (i.hasNext()) {
FileItem fi = (FileItem) i.next();
String fileName = fi.getName();
if (fileName != null) {
File fullFile = new File(new String(fi.getName().getBytes(), "utf-8")); // 解决文件名乱码问题
File savedFile = new File(uploadPath, fullFile.getName());
fi.write(savedFile);
}
}
System.out.print("upload succeed");
} catch (Exception e) {

}
}
}