在這里，我們將學(xué)習(xí)如何使用Servlet處理文件上傳到服務(wù)器。要將文件上傳到服務(wù)器，html文件中表單的方法必須指定為：post，并且enctype必須是multipart/form-data。 例如：
<form action="go" method="post" enctype="multipart/form-data">
注意：
method和enctype指定的值不正確，文件將無法正常上傳和接收。
要將文件上傳到服務(wù)器，有多種方法可以完成這個(gè)工作。但是，將使用由oreilly提供的MultipartRequest類。對(duì)于使用此類，必須有cos.jar文件。如果下載這個(gè)例子的項(xiàng)目代碼，我們已經(jīng)在項(xiàng)目目錄WEB-INF/lib附帶了cos.jar文件。
打開Eclipse，創(chuàng)建一個(gè)動(dòng)態(tài)Web項(xiàng)目：UploadFileHandle，其完整的目錄結(jié)構(gòu)如下所示 -
以下是這個(gè)項(xiàng)目中的幾個(gè)主要的代碼文件。
文件：index.html
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>文件上傳示例</title>
</head>
<body>
<div style="margin: auto; text-align: center">
<form action="upload" method="post" enctype="multipart/form-data">
選擇文件:<input type="file" name="fname" /><input type="submit"
value="上傳" />
</form>
</div>
</body>
</html>
文件：UploadServlet.java
package com.yiibai;
import java.io.*;
import java.util.Enumeration;
import javax.servlet.ServletException;
import javax.servlet.http.*;
import com.oreilly.servlet.MultipartRequest;
public class UploadServlet extends HttpServlet {
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setCharacterEncoding("UTF-8");
response.setContentType("text/html;charset=UTF-8");
request.setCharacterEncoding("UTF-8");
PrintWriter out = response.getWriter();
// String dir = System.getProperty("user.dir")+"/uploads";
String dir = request.getSession().getServletContext().getRealPath("");
System.out.println("Save to path: " + dir);
MultipartRequest mr = new MultipartRequest(request, dir);
// 傳回所有文件輸入類型的名稱
Enumeration files = mr.getFileNames();
String fileName = "";
String filePath = "";
while (files.hasMoreElements()) {
fileName = (String) files.nextElement();
System.out.println("FileName = " + fileName);
// 用此方法得到上傳文件的真正的文件名，這里的fileName指文件輸入類型的名稱
filePath = mr.getFilesystemName(fileName);
System.out.println("FilePath = " + filePath);
// 此方法得到一個(gè)文件對(duì)象，代表儲(chǔ)存在服務(wù)器上的fileName文件
File f = mr.getFile(fileName);
if (null == f) {
throw new ServletException("file is not exist");
}
}
out.print("successfully uploaded");
out.close();
}
}
注意：
在MultipartRequest類構(gòu)造函數(shù)中傳遞了兩個(gè)參數(shù)，第一個(gè)是HttpServletRequest對(duì)象，第二個(gè)是String對(duì)象(指定存儲(chǔ)目錄位置)。在這里假設(shè)在當(dāng)前項(xiàng)目文件下存儲(chǔ)上傳的文件。
文件：web.xml
此配置文件提供有關(guān)servlet的信息。
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
id="WebApp_ID" version="3.1">
<display-name>UploadFileHandle</display-name>
<welcome-file-list>
<welcome-file>index.html</welcome-file>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>UploadServlet</servlet-name>
<servlet-class>com.yiibai.UploadServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>UploadServlet</servlet-name>
<url-pattern>/upload</url-pattern>
</servlet-mapping>
</web-app>
在編寫上面代碼后，部署此Web應(yīng)用程序(在項(xiàng)目名稱上點(diǎn)擊右鍵->”Run On Server…”)，打開瀏覽器訪問URL： http://localhost:8080/UploadHandle/ ，如果沒有錯(cuò)誤，應(yīng)該會(huì)看到以下結(jié)果 -
在選擇好要上傳文件后，提交上傳，打開項(xiàng)目部署的目錄，將會(huì)看到文件已經(jīng)上傳成功 -
同時(shí)在終端上也輸出以下有關(guān)文件的信息：
Save to path: F:\worksp\servlet\.metadata\.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\UploadFileHandle\
FileName = fname
FilePath = 0171015223409.png
以下是UploadServlet的源代碼，可以一次處理多個(gè)文件上傳。在進(jìn)行之前，請(qǐng)確保以下內(nèi)容準(zhǔn)備完成 -
FileUpload，因此請(qǐng)確保類路徑中有最新版本的commons-fileupload.x.x.jar文件?？梢詮?http://commons.apache.org/fileupload/ 下載。FileUpload上傳組件取決于Commons IO，因此請(qǐng)確保類路徑中有最新版本的commons-io-x.x.jar文件，可以從 http://commons.apache.org/io/ 下載。maxFileSize，否則將不會(huì)上傳文件。確保提前創(chuàng)建目錄C:\temp和webapps\data，如何實(shí)現(xiàn)請(qǐng)參考以下代碼 -
// 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.");
}
}
}
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