How to convert String to File object

[Darren Alexandria]

Good day!

I have a code that lists the contents of a directory.

  
//Generate the List of Files in a Directory
File dir = new File("C:/UploadedFiles", filename);
// The list of files can also be retrieved as File objects
String[] children = dir.list();
    
if (children == null) 
  {
System.out.println("Either dir does not exist or is not a directory");
  } 
else  { 
System.out.println("There are files found in the directory");
  for (int i=0; i<children.length; i++) 
    {
        // Get filename of file or directory
           filename = children[i];
           System.out.println("LIST : " + filename);
            

I after listing the filenames, I want them to be converted to Files or File Object. And save it to the database. Is it possible?

I have tried this one and append it to the code above but it didn't work:

File file = new File (filename);
String filen = fi.getName();
long size = fi.getSize();
String fname = filen.substring(filen.lastIndexOf(java.io.File.separator)+1);
 System.out.println("FILE : " + fname + "    SIZE : " + size + " bytes");
            
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver").newInstance();
connection = DriverManager.getConnection(connectionURL, " ", " ");
statement = connection.createStatement();
String sql = "INSERT INTO tblTestFiles("
                              + "strFileName,"
                              + "imgFile) "
              + "VALUES(?,?)";
PreparedStatement pstmt = connection.prepareStatement(sql);
pstmt.setString(1,fname);
        
// Set the blob
FileInputStream is = new FileInputStream(file);
pstmt.setBinaryStream(2, is, (int)file.length());

// Insert the row
 pstmt.executeUpdate();

Stack trace:


java.lang.NullPointerException
at org.apache.jsp.HttpUploadDB_jsp._jspService(HttpUploadDB_jsp.java:148)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:328)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:315)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:210)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:151)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:870)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685)
at java.lang.Thread.run(Thread.java:595)
java.lang.NullPointerException


Thanks.

[Jim Yingst]

What is this, all in a JSP page? I recommend that you move this code into a class so you can test it better. In particular, what line is that error message coming from?

To get a File object rather than a String filename, you should probably include the parent directory:

File file = new File (dir, filename);

Or to make this easier, just use listFiles() rather than list() in the first place.

[Darren Alexandria]

Thanks so much for your reply. Yes, I will move my codes in servlets within the week but as of now I placed it in JSPs for testing purposes.

I followed your advice and modified the code:

 File[] files = dir.listFiles();    
if (files == null) 
{
System.out.println("Either dir does not exist or is not a directory");
} 
else 
{
System.out.println("There are files found in the directory");
for (int i=0; i<files.length; i++) 
{
// Get filename of file or directory
filename = files[i];
System.out.println("LIST : " + filename);
File file = new File ("C:/UploadedFiles", filename);

But I am not able to iterate it in here.

filename = files[i];

Is says, "Cannot convert from File to String".

Thanks again.

Darren
[ September 10, 2007: Message edited by: Darren Alexandria ]

[Freddy Wong]

filename = files[i];

Is filename a String? If yes, then it definitely won't work. You can't assigned a File object into a String object. If you want to get the file name, you can do this:

    
filename = files[i].getName();

I want them to be converted to Files or File Object. And save it to the database.

You shouldn't do that. If you want to save the files into the database, you should save the content of the file and not the File object.
[ September 10, 2007: Message edited by: Freddy Wong ]

[mohsen fakhari]

as jim said it is hard to say what causes this NullPointerException before you move the code
into a separate class.Or at least you can insert some try/catch statements.
And as I understood all what you need is the file name(the last part of complete path) and
its size,right?
Isn't it better to define children like this:

File[] children = dir.listFiles();

And then you can print children[i].getName() in your loop and use chldren[i].length() when
you need.

[Darren Alexandria]

Wow, thanks to your replies. I was really enlightened. All the while I thought that I can get the contents of the file using File Object. Actually, what I am trying to do is this: The client uploads files to the server's file system. After that, those will will be retrieved and then be uploaded to the database.
Is that sensible? or Can I do it in from Client and save it straight to the database? I have made some code with that process using HttpClient and FileUpload but it always ends up with "File Not Found".

Please give me advice.
Thanks.

Darren