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：

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) {

	}
}

}