DZone Snippets: Frost137's Code Snippets

Java Cons class

frost137 (Douglas Wyatt) — Mon, 21 Apr 2008 23:43:50 GMT

Very simple Cons class for Java



public class Cons

{

    private T car;

    private U cdr;



    public Cons( T carArg, U cdrArg )

    {

        car = carArg;

        cdr = cdrArg;

    }



    public T getCar(){ return car; }

    public U getCdr(){ return cdr; }

}

Common keytool commands needed for living with Java

frost137 (Douglas Wyatt) — Mon, 14 Apr 2008 18:06:50 GMT



// generate a key -- make it long lived so we dont have to do this again

keytool -genkey -alias tomcat -keyalg RSA -validity 3650 -storepass changeit



// export cert to a file

keytool -export -rfc -v -file tomcatCert.crt -alias tomcat -storepass changeit

 

// look at the cert in the file

keytool -printcert -file tomcatCert.crt -storepass changeit





// delete pre-existing cert

keytool -delete -alias tomcat -keystore c:/apps/jdk/jre/lib/security/cacerts -storepass changeit



// import cert into a keystore

keytool -import -file tomcatCert.crt -trustcacerts -alias tomcat -keystore c:/apps/jdk/jre/lib/security/cacerts -storepass changeit



// look at the imported cert

keytool -list -alias tomcat -keystore c:/apps/jdk/jre/lib/security/cacerts -storepass changeit

Convert Java date to GMT

frost137 (Douglas Wyatt) — Fri, 28 Mar 2008 20:56:15 GMT

This function converts a local date to GMT. This version corrects the bug common to this type of conversion where the date is incorrectly converted when the time is close to the DST crossover.



private static Date cvtToGmt( Date date )

{

   TimeZone tz = TimeZone.getDefault();

   Date ret = new Date( date.getTime() - tz.getRawOffset() );



   // if we are now in DST, back off by the delta.  Note that we are checking the GMT date, this is the KEY.

   if ( tz.inDaylightTime( ret ))

   {

      Date dstDate = new Date( ret.getTime() - tz.getDSTSavings() );



      // check to make sure we have not crossed back into standard time

      // this happens when we are on the cusp of DST (7pm the day before the change for PDT)

      if ( tz.inDaylightTime( dstDate ))

      {

         ret = dstDate;

      }

   }



   return ret;

}

Drop an unnamed constraint from SqlServer 2000

frost137 (Douglas Wyatt) — Wed, 12 Mar 2008 22:00:43 GMT

// description of your code here



declare @name nvarchar(32), 

    @sql nvarchar(1000)



-- find constraint name

select @name = O.name 

from sysobjects AS O

left join sysobjects AS T

    on O.parent_obj = T.id

where isnull(objectproperty(O.id,'IsMSShipped'),1) = 0

    and O.name not like '%dtproper%'

    and O.name not like 'dt[_]%'

    and T.name = 'MyTable'

    and O.name like 'DF__MyTable__MyColu%'



-- delete if found

if not @name is null

begin

    select @sql = 'ALTER TABLE [MyTable] DROP CONSTRAINT [' + @name + ']'

    execute sp_executesql @sql

end



-- do your ALTER TABLE here



-- replace the constraint

select @sql = 'ALTER TABLE [MyTable] ADD CONSTRAINT [' + @name + '] DEFAULT (0) FOR [MyColumn]'

execute sp_executesql @sql

Easiest way to do a POST test from Java

frost137 (Douglas Wyatt) — Wed, 12 Mar 2008 00:05:42 GMT

I need to test services with POST transactions. Using HTML to do it is the easiest way, constructed in Java (that part isn't necessary unless the args are somehow cooked or just too complex to trust hand-crafted HTML).



// write the HTML code out to stdout -- leave it to the user to redirect

System.out.print( "System.out.print(  compId );

System.out.print( "\"/>System.out.print( ids );

System.out.print( "\"/>" );

System.out.print( "" );

System.out.println();

Java filecopy using NIO

frost137 (Douglas Wyatt) — Fri, 04 Jan 2008 22:40:01 GMT



    public static void fileCopy( File in, File out )

            throws IOException

    {

        FileChannel inChannel = new FileInputStream( in ).getChannel();

        FileChannel outChannel = new FileOutputStream( out ).getChannel();

        try

        {

//          inChannel.transferTo(0, inChannel.size(), outChannel);      // original -- apparently has trouble copying large files on Windows



            // magic number for Windows, 64Mb - 32Kb)

            int maxCount = (64 * 1024 * 1024) - (32 * 1024);

            long size = inChannel.size();

            long position = 0;

            while ( position < size )

            {

               position += inChannel.transferTo( position, maxCount, outChannel );

            }

        }

        finally

        {

            if ( inChannel != null )

            {

               inChannel.close();

            }

            if ( outChannel != null )

            {

                outChannel.close();

            }

        }

    }

Example file download servlet

frost137 (Douglas Wyatt) — Tue, 09 Oct 2007 23:12:04 GMT

// description of your code here



  /**

     *  Sends a file to the ServletResponse output stream.  Typically

     *  you want the browser to receive a different name than the

     *  name the file has been saved in your local database, since

     *  your local names need to be unique.

     *

     *  @param req The request

     *  @param resp The response

     *  @param filename The name of the file you want to download.

     *  @param original_filename The name the browser should receive.

     */

    private void doDownload( HttpServletRequest req, HttpServletResponse resp,

                             String filename, String original_filename )

        throws IOException

    {

        File                f        = new File(filename);

        int                 length   = 0;

        ServletOutputStream op       = resp.getOutputStream();

        ServletContext      context  = getServletConfig().getServletContext();

        String              mimetype = context.getMimeType( filename );



        //

        //  Set the response and go!

        //

        //

        resp.setContentType( (mimetype != null) ? mimetype : "application/octet-stream" );

        resp.setContentLength( (int)f.length() );

        resp.setHeader( "Content-Disposition", "attachment; filename=\"" + original_filename + "\"" );



        //

        //  Stream to the requester.

        //

        byte[] bbuf = new byte[BUFSIZE];

        DataInputStream in = new DataInputStream(new FileInputStream(f));



        while ((in != null) && ((length = in.read(bbuf)) != -1))

        {

            op.write(bbuf,0,length);

        }



        in.close();

        op.flush();

        op.close();

    }

Get a String version of a stacktrace

frost137 (Douglas Wyatt) — Thu, 20 Sep 2007 21:00:14 GMT

// Get a String version of a stacktrace



    Throwable t = new Throwable();  // test code



    final Writer result = new StringWriter();

    final PrintWriter printWriter = new PrintWriter(result);

    t.printStackTrace(printWriter);

    result.toString();