当我在学习JavaWeb文件上传的时候,我就一直有一个疑问,网站上那些博客的图片是怎么上传的,因为当提交了表单之后网页就跳转了。后来我学习到了Ajax,我知道了浏览器可以异步的发送响应,这时我又有新的疑问,那就是在我上传一些文件的时候,那些网站的上传进度是怎么做到的,因为servlet直到上传完成之后才完成响应。
最近我们的项目中有一个地方中需要用到一个功能,当用户点击一个处理按钮时,前台会实时的显示后台处理动态,由于servlet一次只能接受一个请求,而且在servlet的生命周期结束时才会把响应数据发送到前台(这一点大家可以做个这样的测试:
1 response.getWriter().print("hello"); 2 Thread.sleep(10000); 3 response.getWriter().print("world");
,你们会发现前台在等待了约10s后收到了"helloworld")。所以我想到了一个方法:使用单例保存实时信息。具体的实现方法就是,当用户点击了处理按钮时,在后台开启一个线程进行处理,并且每进行到一步,就向单例中写入当前状态信息。然后编写一个servlet,用于返回单例中的信息,前台循环发送请求,这样就能实现实时显示进度的效果。
好了,啰嗦了这么多,下面进入正题,如何实现上传文件动态显示进度,其实思想和上面的功能是一致的,我将这个功能分为三个点:
- 单例:用于保存进度信息;
- 上传servlet:用于上传文件并实时写入进度;
- 进度servlet:用于读取实时进度信息;
上代码,前台:
1
<!
DOCTYPE html
>
2 < html >
3 < head >
4 < meta charset ="UTF-8" >
5 < title >Insert title here </ title >
6 < style type ="text/css" >
7 #progress:after {
8 content : '%' ;
9 }
10 </ style >
11 </ head >
12 < body >
13 < h3 >File upload demo </ h3 >
14 < form action ="TestServlet" method ="post" enctype ="multipart/form-data" id ="dataForm" >
15 < input type ="file" name ="file" id ="fileInput" > < br >
16 < input type ="submit" value ="submit" id ="submit" >
17 </ form >
18 < div id ="progress" ></ div >
19 < script type ="text/javascript" src ="scripts/jquery-1.9.1.min.js" ></ script >
20 < script type ="text/javascript" >
21 ( function () {
22 var form = document.getElementById( " dataForm " );
23 var progress = document.getElementById( " progress " );
24
25 $( " #submit " ).click( function (event) {
26 // 阻止默认事件
27 event.preventDefault();
28 // 循环查看状态
29 var t = setInterval( function (){
30 $.ajax({
31 url: ' ProgressServlet ' ,
32 type: ' POST ' ,
33 dataType: ' text ' ,
34 data: {
35 filename: fileInput.files[ 0 ].name,
36 },
37 success: function (responseText) {
38 var data = JSON.parse(responseText);
39 // 前台更新进度
40 progress.innerText = parseInt((data.progress / data.size) * 100 );
41 },
42 error: function (){
43 console.log( " error " );
44 }
45 });
46 }, 500 );
47 // 上传文件
48 $.ajax({
49 url: ' UploadServlet ' ,
50 type: ' POST ' ,
51 dataType: ' text ' ,
52 data: new FormData(form),
53 processData: false ,
54 contentType: false ,
55 success: function (responseText) {
56 // 上传完成,清除循环事件
57 clearInterval(t);
58 // 将进度更新至100%
59 progress.innerText = 100 ;
60 },
61 error: function (){
62 console.log( " error " );
63 }
64 });
65 return false ;
66 });
67 })();
68 </ script >
69 </ body >
70 </ html >
2 < html >
3 < head >
4 < meta charset ="UTF-8" >
5 < title >Insert title here </ title >
6 < style type ="text/css" >
7 #progress:after {
8 content : '%' ;
9 }
10 </ style >
11 </ head >
12 < body >
13 < h3 >File upload demo </ h3 >
14 < form action ="TestServlet" method ="post" enctype ="multipart/form-data" id ="dataForm" >
15 < input type ="file" name ="file" id ="fileInput" > < br >
16 < input type ="submit" value ="submit" id ="submit" >
17 </ form >
18 < div id ="progress" ></ div >
19 < script type ="text/javascript" src ="scripts/jquery-1.9.1.min.js" ></ script >
20 < script type ="text/javascript" >
21 ( function () {
22 var form = document.getElementById( " dataForm " );
23 var progress = document.getElementById( " progress " );
24
25 $( " #submit " ).click( function (event) {
26 // 阻止默认事件
27 event.preventDefault();
28 // 循环查看状态
29 var t = setInterval( function (){
30 $.ajax({
31 url: ' ProgressServlet ' ,
32 type: ' POST ' ,
33 dataType: ' text ' ,
34 data: {
35 filename: fileInput.files[ 0 ].name,
36 },
37 success: function (responseText) {
38 var data = JSON.parse(responseText);
39 // 前台更新进度
40 progress.innerText = parseInt((data.progress / data.size) * 100 );
41 },
42 error: function (){
43 console.log( " error " );
44 }
45 });
46 }, 500 );
47 // 上传文件
48 $.ajax({
49 url: ' UploadServlet ' ,
50 type: ' POST ' ,
51 dataType: ' text ' ,
52 data: new FormData(form),
53 processData: false ,
54 contentType: false ,
55 success: function (responseText) {
56 // 上传完成,清除循环事件
57 clearInterval(t);
58 // 将进度更新至100%
59 progress.innerText = 100 ;
60 },
61 error: function (){
62 console.log( " error " );
63 }
64 });
65 return false ;
66 });
67 })();
68 </ script >
69 </ body >
70 </ html >
后台,单例:
1
import
java.util.Hashtable;
2
3 public class ProgressSingleton {
4 // 为了防止多用户并发,使用线程安全的Hashtable
5 private static Hashtable<Object, Object> table = new Hashtable<> ();
6
7 public static void put(Object key, Object value){
8 table.put(key, value);
9 }
10
11 public static Object get(Object key){
12 return table.get(key);
13 }
14
15 public static Object remove(Object key){
16 return table.remove(key);
17 }
18 }
2
3 public class ProgressSingleton {
4 // 为了防止多用户并发,使用线程安全的Hashtable
5 private static Hashtable<Object, Object> table = new Hashtable<> ();
6
7 public static void put(Object key, Object value){
8 table.put(key, value);
9 }
10
11 public static Object get(Object key){
12 return table.get(key);
13 }
14
15 public static Object remove(Object key){
16 return table.remove(key);
17 }
18 }
上传servlet:
1
import
java.io.File;
2 import java.io.FileOutputStream;
3 import java.io.IOException;
4 import java.io.InputStream;
5 import java.util.List;
6
7 import javax.servlet.ServletException;
8 import javax.servlet.annotation.WebServlet;
9 import javax.servlet.http.HttpServlet;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse; 12
13 import org.apache.tomcat.util.http.fileupload.FileItem;
14 import org.apache.tomcat.util.http.fileupload.FileUploadException;
15 import org.apache.tomcat.util.http.fileupload.disk.DiskFileItemFactory;
16 import org.apache.tomcat.util.http.fileupload.servlet.ServletFileUpload; 17 import org.apache.tomcat.util.http.fileupload.servlet.ServletRequestContext;
18
19 import singleton.ProgressSingleton;
20
21 @WebServlet("/UploadServlet" )
22 public class UploadServlet extends HttpServlet {
23 private static final long serialVersionUID = 1L ;
24
25 public UploadServlet() {
26 }
27
28 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
29
30 DiskFileItemFactory factory = new DiskFileItemFactory();
31 factory.setSizeThreshold(4*1024 );
32
33 ServletFileUpload upload = new ServletFileUpload(factory);
34
35 List<FileItem> fileItems;
36 try {
37 fileItems = upload.parseRequest( new ServletRequestContext(request));
38 // 获取文件域
39 FileItem fileItem = fileItems.get(0 );
40 // 使用sessionid + 文件名生成文件号
41 String id = request.getSession().getId() + fileItem.getName();
42 // 向单例哈希表写入文件长度和初始进度
43 ProgressSingleton.put(id + "Size" , fileItem.getSize());
44 // 文件进度长度
45 long progress = 0 ;
46 // 用流的方式读取文件,以便可以实时的获取进度
47 InputStream in = fileItem.getInputStream();
48 File file = new File("D:/test" );
49 file.createNewFile();
50 FileOutputStream out = new FileOutputStream(file);
51 byte[] buffer = new byte[1024 ];
52 int readNumber = 0 ;
53 while((readNumber = in.read(buffer)) != -1 ){
54 // 每读取一次,更新一次进度大小
55 progress = progress + readNumber;
56 // 向单例哈希表写入进度
57 ProgressSingleton.put(id + "Progress" , progress);
58 out.write(buffer);
59 }
60 // 当文件上传完成之后,从单例中移除此次上传的状态信息
61 ProgressSingleton.remove(id + "Size" );
62 ProgressSingleton.remove(id + "Progress" );
63 in.close();
64 out.close();
65 } catch (FileUploadException e) {
66 e.printStackTrace();
67 }
68
69 response.getWriter().print("done" );
70 }
71
72 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
73 doGet(request, response);
74 }
75
76 }
2 import java.io.FileOutputStream;
3 import java.io.IOException;
4 import java.io.InputStream;
5 import java.util.List;
6
7 import javax.servlet.ServletException;
8 import javax.servlet.annotation.WebServlet;
9 import javax.servlet.http.HttpServlet;
10 import javax.servlet.http.HttpServletRequest;
11 import javax.servlet.http.HttpServletResponse; 12
13 import org.apache.tomcat.util.http.fileupload.FileItem;
14 import org.apache.tomcat.util.http.fileupload.FileUploadException;
15 import org.apache.tomcat.util.http.fileupload.disk.DiskFileItemFactory;
16 import org.apache.tomcat.util.http.fileupload.servlet.ServletFileUpload; 17 import org.apache.tomcat.util.http.fileupload.servlet.ServletRequestContext;
18
19 import singleton.ProgressSingleton;
20
21 @WebServlet("/UploadServlet" )
22 public class UploadServlet extends HttpServlet {
23 private static final long serialVersionUID = 1L ;
24
25 public UploadServlet() {
26 }
27
28 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
29
30 DiskFileItemFactory factory = new DiskFileItemFactory();
31 factory.setSizeThreshold(4*1024 );
32
33 ServletFileUpload upload = new ServletFileUpload(factory);
34
35 List<FileItem> fileItems;
36 try {
37 fileItems = upload.parseRequest( new ServletRequestContext(request));
38 // 获取文件域
39 FileItem fileItem = fileItems.get(0 );
40 // 使用sessionid + 文件名生成文件号
41 String id = request.getSession().getId() + fileItem.getName();
42 // 向单例哈希表写入文件长度和初始进度
43 ProgressSingleton.put(id + "Size" , fileItem.getSize());
44 // 文件进度长度
45 long progress = 0 ;
46 // 用流的方式读取文件,以便可以实时的获取进度
47 InputStream in = fileItem.getInputStream();
48 File file = new File("D:/test" );
49 file.createNewFile();
50 FileOutputStream out = new FileOutputStream(file);
51 byte[] buffer = new byte[1024 ];
52 int readNumber = 0 ;
53 while((readNumber = in.read(buffer)) != -1 ){
54 // 每读取一次,更新一次进度大小
55 progress = progress + readNumber;
56 // 向单例哈希表写入进度
57 ProgressSingleton.put(id + "Progress" , progress);
58 out.write(buffer);
59 }
60 // 当文件上传完成之后,从单例中移除此次上传的状态信息
61 ProgressSingleton.remove(id + "Size" );
62 ProgressSingleton.remove(id + "Progress" );
63 in.close();
64 out.close();
65 } catch (FileUploadException e) {
66 e.printStackTrace();
67 }
68
69 response.getWriter().print("done" );
70 }
71
72 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
73 doGet(request, response);
74 }
75
76 }
进度servlet:
1
import
java.io.IOException;
2
3 import javax.servlet.ServletException;
4 import javax.servlet.annotation.WebServlet;
5 import javax.servlet.http.HttpServlet;
6 import javax.servlet.http.HttpServletRequest;
7 import javax.servlet.http.HttpServletResponse; 8
9 import net.sf.json.JSONObject;
10 import singleton.ProgressSingleton;
11
12 @WebServlet("/ProgressServlet" )
13 public class ProgressServlet extends HttpServlet {
14 private static final long serialVersionUID = 1L ;
15
16 public ProgressServlet() {
17 super ();
18 // TODO Auto-generated constructor stub
19 }
20
21 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
22
23 String id = request.getSession().getId();
24 String filename = request.getParameter("filename" );
25 // 使用sessionid + 文件名生成文件号,与上传的文件保持一致
26 id = id + filename;
27 Object size = ProgressSingleton.get(id + "Size" );
28 size = size == null ? 100 : size;
29 Object progress = ProgressSingleton.get(id + "Progress" );
30 progress = progress == null ? 0 : progress;
31 JSONObject json = new JSONObject();
32 json.put("size" , size);
33 json.put("progress" , progress);
34 response.getWriter().print(json.toString());
35 }
36
37 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
38 doGet(request, response);
39 }
40
41 }
2
3 import javax.servlet.ServletException;
4 import javax.servlet.annotation.WebServlet;
5 import javax.servlet.http.HttpServlet;
6 import javax.servlet.http.HttpServletRequest;
7 import javax.servlet.http.HttpServletResponse; 8
9 import net.sf.json.JSONObject;
10 import singleton.ProgressSingleton;
11
12 @WebServlet("/ProgressServlet" )
13 public class ProgressServlet extends HttpServlet {
14 private static final long serialVersionUID = 1L ;
15
16 public ProgressServlet() {
17 super ();
18 // TODO Auto-generated constructor stub
19 }
20
21 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
22
23 String id = request.getSession().getId();
24 String filename = request.getParameter("filename" );
25 // 使用sessionid + 文件名生成文件号,与上传的文件保持一致
26 id = id + filename;
27 Object size = ProgressSingleton.get(id + "Size" );
28 size = size == null ? 100 : size;
29 Object progress = ProgressSingleton.get(id + "Progress" );
30 progress = progress == null ? 0 : progress;
31 JSONObject json = new JSONObject();
32 json.put("size" , size);
33 json.put("progress" , progress);
34 response.getWriter().print(json.toString());
35 }
36
37 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
38 doGet(request, response);
39 }
40
41 }
效果图: