翻譯:使用Servlet實現文件上傳
原文地址:http://www.tutorialspoint.com/servlets/servlets-file-uploading.htm
一個Servlet可以通過HTML表單標簽將文件上傳到服務器。支待上傳的有文本、圖像及任何文件。
創建文件上傳表單:
下面的html代碼創建了一個上傳表單。創建過程需要注意以下幾點:
l form標簽中的method屬性必須設置為POST,即GET方法是不可以的。
l form標簽中的enctype屬性應該設置為multipart/form-data。
l from標簽中的action屬性應該與服務器后臺的servlet映射路徑相同。接下來的實例,我們將使用UploadServlet實現文件上傳。
l 要上傳一個文件,你應該使用一個<input type=”file”.../>標記。要多個文件上傳,必須包含多個具有不同的名稱屬性值的<input type=”file”.../>標記。The browser associates a Browse button with each of them。
<html> <head> <title>File Uploading Form</title> </head> <body> <h3>File Upload:</h3> Select a file to upload: <br /> <form action="UploadServlet" method="post" enctype="multipart/form-data"> <input type="file" name="file" size="50" /> <br /> <input type="submit" value="Upload File" /> </form> </body> </html> |
以上代碼將得到以下效果。你可以在本地PC上選擇一個文件。當你點擊“Upload File”,表單將會隨著你選擇的文件一起被提交。
后臺servlet:
以下UploadServlet servlet將接收上傳的文件并將其保存入<Tomcat-installation-directory>/webapps/data文件夾。這個文件夾的名稱可以通過外部配置文件web.xml中的context-param元素內容增加。代碼如下:
<web-app>
....
<context-param>
<description>Location to store uploaded file</description>
<param-name>file-upload</param-name>
<param-value>
c:"apache-tomcat-5.5.29"webapps"data"
</param-value>
</context-param>
....
</web-app>
|
以下是實現了多文件同時上傳功能的UploadServlet。在此之前您必須確定以下幾點:
l 以下實例依賴F ileUpload類,所以您須將最新版的commons-fileupload.x.x.jar放到您的classpath下。可以從這里下載:http://commons.apache.org/fileupload/。
l FileUpload類依賴于Commons IO包,所以您須將最新版commons-fileupload.x.x.jar放到您的classpath下。可以從這里下載:http://commons.apache.org/io/。
l 在測試以下例子的時候,您應該上傳小于maxFileSize的文件,否則無法上傳。
l 事先確定你已經建議好文件夾:c:"temp和c:"apache-tomcat-5.5.29"webapps"data。
// Import required java libraries
import java.io.*;
import java.util.*;
import javax.servlet.ServletConfig;
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.FileUploadException;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import org.apache.commons.io.output.*;
public class UploadServlet extends HttpServlet {
private boolean isMultipart;
private String filePath;
private int maxFileSize = 50 * 1024;
private int maxMemSize = 4 * 1024;
private File file ;
public void init( ){
// Get the file location where it would be stored.
filePath =
getServletContext().getInitParameter("file-upload");
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, java.io.IOException {
// Check that we have a file upload request
isMultipart = ServletFileUpload.isMultipartContent(request);
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter( );
if( !isMultipart ){
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet upload</title>");
out.println("</head>");
out.println("<body>");
out.println("<p>No file uploaded</p>");
out.println("</body>");
out.println("</html>");
return;
}
DiskFileItemFactory factory = new DiskFileItemFactory();
// maximum size that will be stored in memory
factory.setSizeThreshold(maxMemSize);
// Location to save data that is larger than maxMemSize.
factory.setRepository(new File("c:""temp"));
// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);
// maximum file size to be uploaded.
upload.setSizeMax( maxFileSize );
try{
// Parse the request to get file items.
List fileItems = upload.parseRequest(request);
// Process the uploaded file items
Iterator i = fileItems.iterator();
out.println("<html>");
out.println("<head>");
out.println("<title>Servlet upload</title>");
out.println("</head>");
out.println("<body>");
while ( i.hasNext () )
{
FileItem fi = (FileItem)i.next();
if ( !fi.isFormField () )
{
// Get the uploaded file parameters
String fieldName = fi.getFieldName();
String fileName = fi.getName();
String contentType = fi.getContentType();
boolean isInMemory = fi.isInMemory();
long sizeInBytes = fi.getSize();
// Write the file
if( fileName.lastIndexOf("""") >= 0 ){
file = new File( filePath +
fileName.substring( fileName.lastIndexOf(""""))) ;
}else{
file = new File( filePath +
fileName.substring(fileName.lastIndexOf("""")+1)) ;
}
fi.write( file ) ;
out.println("Uploaded Filename: " + fileName + "<br>");
}
}
out.println("</body>");
out.println("</html>");
}catch(Exception ex) {
System.out.println(ex);
}
}
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, java.io.IOException {
throw new ServletException("GET method used with " +
getClass( ).getName( )+": POST method required.");
}
}
|
編譯并運行Servlet
編譯以上UploadServlet并在web.xml中創建必須的實體,如下:
<servlet>
<servlet-name>UploadServlet</servlet-name>
<servlet-class>UploadServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>UploadServlet</servlet-name>
<url-pattern>/UploadServlet</url-pattern>
</servlet-mapping>
|
現在可以嘗試使用你創建的HTML表單上傳文件。當你訪問http://localhost:8080/UploadFile.htm,瀏覽器里將會顯示如下效果,您可以從本地上傳你想要上傳的任何文件。
如果您的servlet腳本運行成功,您的文件上傳在c:"apache-tomcat-5.5.29"webapps"data"directory文件夾。
posted on 2011-03-23 08:52 jack zhai 閱讀(3810) 評論(0) 編輯 收藏 所屬分類: 翻譯