📅 最后修改于: 2020-11-12 05:42:59 🧑 作者: Mango
Servlet可以与HTML表单标签一起使用，以允许用户将文件上传到服务器。上传的文件可以是文本文件或图像文件，也可以是任何文档。
下面的以下HTM代码创建一个上载器表单。以下是要注意的重点-
表单方法属性应设置为POST方法，并且不能使用GET方法
表单enctype属性应设置为multipart / form-data 。
表单操作属性应设置为Servlet文件，该文件将处理后端服务器上的文件上传。以下示例是使用UploadServlet servlet上载文件。
要上传单个文件，您应该使用属性类型为“ file”的单个标记。要允许上传多个文件，请包含多个输入标签，这些输入标签的name属性值不同。浏览器将“浏览”按钮与每个按钮相关联。
File Uploading Form
File Upload:
Select a file to upload:
这将显示以下结果，该结果将允许从本地PC选择文件，并且当用户单击“上传文件”时，表单将与所选fil一起提交-
File Upload:
Select a file to upload:
NOTE: This is just dummy form and would not work.
以下是Servlet UploadServlet ，它将负责接受上载的文件并将其存储在目录
....
Location to store uploaded file
file-upload
c:\apache-tomcat-5.5.29\webapps\data\
....
以下是UploadServlet的源代码，它可以一次处理多个文件的上载。在继续之前，请确保以下内容-
以下示例取决于FileUpload，因此请确保您在类路径中具有commons-fileupload.xxjar文件的最新版本。您可以从https://commons.apache.org/fileupload/下载。
FileUpload取决于Commons IO，因此请确保您在类路径中具有commons-io-xxjar文件的最新版本。您可以从https://commons.apache.org/io/下载。
在测试以下示例时，应上传大小小于maxFileSize的文件，否则将不会上传文件。
确保您已经预先创建了目录c：\ temp和c：\ apache-tomcat8.0.28 \ 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("");
out.println("");
out.println("Servlet upload ");
out.println("");
out.println("");
out.println("No file uploaded
");
out.println("");
out.println("");
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("");
out.println("");
out.println("Servlet upload ");
out.println("");
out.println("");
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 + "
");
}
}
out.println("");
out.println("");
} 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.");
}
}
}
编译上面的Servlet UploadServlet并在web.xml文件中创建所需的条目，如下所示。
UploadServlet
UploadServlet
UploadServlet
/UploadServlet
现在，尝试使用上面创建的HTML表单上传文件。当您尝试http：// localhost：8080 / UploadFile.htm时，它将显示以下结果，这将帮助您从本地计算机上载任何文件。
File Upload:
Select a file to upload:
如果您的Servlet脚本运行良好，则应将文件上传到c：\ apache-tomcat8.0.28 \ webapps \ data \目录中。