Do it in two parts, get the file first, then get the byte array from the file.
Have a look at this tutorial for getting the file.
Fie upload to Sevlets
Then look at this trail from the Oracle site for IO and byte streams. Once you've worked through both you should be able to work it out.
Basic I/O
UPDATE
In relation to the comments to this answer, a working implementation using FileInputStream and the File from the server is given below using a slightly modified version of the tutorial. It may not be the best way, but it does work.
package cmpdhoug;
import java.io.*;
import java.util.*;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
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.*;
@WebServlet (
name = "UploadServlet",
urlPatterns = "/UploadServlet",
loadOnStartup = 1
)
public class UploadServlet extends HttpServlet {
private boolean isMultipart;
private String filePath, tempPath;
private int maxFileSize = 5242880;
private int maxMemSize = 5 * 1024;
private File file ;
public void init( ){
// Get the file location where it would be stored.
filePath =
getServletContext().getInitParameter("file-upload");
tempPath = getServletContext().getInitParameter("temp-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(tempPath));
// 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>");
}
}
// Get byte stream from file uploaded to server.
FileInputStream fis = new FileInputStream(file);
byte[] byteArray = new byte[(int) file.length()];
// Add the bytes from the file to the array
for(int j = 0; j < byteArray.length; j++){
byteArray[j] = (byte)fis.read();
// Just to show the bytes are in the array.
System.out.println(byteArray[j]);
}
fis.close();
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.");
}
}
You also need to make sure that you update your web.xml file to provide the correct file paths to wherever your server deploys your app to, which may be different from where the Tomcat installation files are locally. For example my Tomcat installation is in /dave/servers/Tomcat/ but my server deploys to the params given below (make sure you create the webapps/data and webapps/temp folders)
web.xml
<!DOCTYPE web-app PUBLIC
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
"http://java.sun.com/dtd/web-app_2_3.dtd" >
<web-app>
<display-name>Archetype Created Web Application</display-name>
<context-param>
<param-name>file-upload</param-name>
<param-value>/Users/dave/Library/Caches/IntelliJIdea2016.2/tomcat/webapps/data/</param-value>
</context-param>
<context-param>
<param-name>temp-upload</param-name>
<param-value>/Users/dave/Library/Caches/IntelliJIdea2016.2/tomcat/webapps/temp/</param-value>
</context-param>
</web-app>
pom.xml with dependencies
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>UploadServlet</groupId>
<artifactId>UploadServlet</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<name>UploadServlet Maven Webapp</name>
<url>http://maven.apache.org</url>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.1</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>commons-fileupload</groupId>
<artifactId>commons-fileupload</artifactId>
<version>1.3.2</version>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-io</artifactId>
<version>1.3.2</version>
</dependency>
</dependencies>
<build>
<finalName>UploadServlet</finalName>
</build>
index file
<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>
