1 var formData = new FormData();
 2 formData.append("file1",$("#file1")[0].files[0]);//第一个file1代表后台文件属性名，第二个file1表示html中input的id
 3 $.ajax({
 4     type:"post",
 5     url:"ajax/uploadFile",
 6     data:formData,
 7     processData : false, 
 8     contentType : false,
 9     success : function(res) { 
10         console.log(res);
11         if(res=="success"){
12             $("#labResult").text("文件上传成功");
13         }
14     }, 
15     error : function(msg) { 
16         console.log(msg.responsText);
17     } 
18 });

 1 import java.io.File;
 2 import java.io.FileInputStream;
 3 import java.io.FileOutputStream;
 4 import java.io.IOException;
 5 import java.io.InputStream;
 6 import java.io.OutputStream;
 7 
 8 import javax.servlet.http.HttpServletRequest;
 9 import javax.servlet.http.HttpServletResponse;
10 
11 import org.apache.struts2.ServletActionContext;
12 
13 import com.opensymphony.xwork2.ActionContext;
14 import com.opensymphony.xwork2.ActionSupport;
15 
16 public class UploadAction extends ActionSupport{
17     private File file1 ; 
18     private String file1FileName ;//FileName为固定写法
19     public File getFile1() {
20         return file1;
21     }
22     public void setFile1(File file1) {
23         this.file1 = file1;
24     }
25     public String getFile1FileName() {
26         return file1FileName;
27     }
28     public void setFile1FileName(String file1FileName) {
29         this.file1FileName = file1FileName;
30     } 
31     public String uploadFile() throws Exception {  
32         
33         String path = ServletActionContext.getRequest().getServletContext().getRealPath("/WEB-INF/upload");  
34         //查看是否存在目录 不存在则创建
35         File file = new File(path);
36         //如果目录不存在
37         if(!file.exists()){
38             file.mkdirs();
39         }
40         //文件不为空 则上传
41         if(file1!=null){
42             //输出流  
43             OutputStream os = new FileOutputStream(new File(path,file1FileName));  
44             //输入流  
45             InputStream is = new FileInputStream(file1);  
46               
47             byte[] buf = new byte[1024];  
48             int length = 0 ;  
49               
50             while(-1 != (length = is.read(buf) ) )  
51             {  
52                 os.write(buf, 0, length) ;  
53             }  
54             is.close();  
55             os.close();  
56         }  
57         return "success";  
58     }  
59 
60     public void uploadFile(){
61         System.out.println("file1:"+file1+".");
62         System.out.println("file1FileName:"+file1FileName+".");
63         String path="";
64         try {
65             path=uploadFile();
66             HttpServletResponse response = ServletActionContext.getResponse();
67             response.setContentType("text/html;charset=utf-8");
68             response.getWriter().write(path);
69         } catch (Exception e) {
70             e.printStackTrace();
71         }
72     }
73 }

<package name="ajax" extends="json-default" namespace="/ajax">
    <action name="uploadFile" class="包名.UploadAction" method="uploadFile"></action>
</package>