/*******************************************************************************
?*
?* 只運行一個實例
?*
?* Just single instance
?*
?*
?* Author: NeedJava
?*
?* Modified: 2007.08.29
?*
?*
?* 你可以使用此程序于任何地方，但請保留程序作者及注釋的完整。如果你改進了程序，
?*
?* 請在原作者后添加姓名，如：Author: NeedJava/Jack/Mike，版本及修改時間同理。
?*
?******************************************************************************/
public final class SingleInstance
{
? /*****************************************************************************
?? *
?? * 構造函數
?? *
?? ****************************************************************************/
? private SingleInstance()
? {
??? this( "vab", ".vab", "vab" );
? }

? public SingleInstance( String filePrefixName, String fileSuffixName, String directoryName )
? {
??? this.init( filePrefixName, fileSuffixName, directoryName );
? }

? /*****************************************************************************
?? *
?? * 原理：
?? *
?? * 用重定向將標準錯誤輸出流定向到一個日志文件，占用它，使其不能被刪除
?? *
?? * 以后的實例試圖將存在的此日志文件改名并且另存為某個文件夾下
?? *
?? * 如果成功，說明沒有程序占用它（不排除你在用它，缺陷？），正好保存日志
?? *
?? * 如果不成功，退出、renameTo命令有一箭雙雕的作用
?? *
?? ****************************************************************************/
? private final void init( String filePrefixName, String fileSuffixName, String directoryName )
? {
??? if( filePrefixName==null||fileSuffixName==null||directoryName==null )
????? {
??????? exitWithWarning( "Error: Invalid file name.", 10 );
????? }

??? //We need check the fileSuffixName here? From the tail?

??? String fileName=filePrefixName+fileSuffixName;

??? try{ File error=new File( fileName );

???????? if( error.exists() )
?????????? {
???????????? File directory=new File( directoryName );

???????????? String newFileName=directoryName+File.separator+convertMillisecond2DateTime( error.lastModified() )+fileSuffixName;

???????????? //System.out.println( newFileName );

???????????? if( directory.exists() )
?????????????? {
???????????????? if( directory.isDirectory() )
?????????????????? {
???????????????????? //renameTo也是好東東，既可以改名，還可以移文件
???????????????????? if( !error.renameTo( new File( newFileName ) ) )
?????????????????????? {
???????????????????????? exitWithWarning( "Error: The instance already exists, I will exit.", 11 );
?????????????????????? }
?????????????????? }
???????????????? else{ exitWithWarning( "Error: The \'"+directoryName+"\' is not a valid directory.", 21 );
???????????????????? }
?????????????? }
???????????? else{ if( directory.mkdirs() )
???????????????????? {
?????????????????????? //renameTo也是好東東，既可以改名，還可以移文件
?????????????????????? if( !error.renameTo( new File( newFileName ) ) )
???????????????????????? {
?????????????????????????? exitWithWarning( "Error: The instance already exists, I will exit.", 11 );
???????????????????????? }
???????????????????? }
?????????????????? else{ exitWithWarning( "Error: Failed to create the \'"+directoryName+"\' directory.", 22 );
?????????????????????? }
???????????????? }
?????????? }

???????? //重定向標準錯誤輸出流，所有功能全靠它。來，啵一個
???????? System.setErr( new PrintStream( new FileOutputStream( fileName ) ) );
?????? }
??? catch( FileNotFoundException fnfe )
???????? {
?????????? //fnfe.printStackTrace();

?????????? exitWithWarning( fnfe.toString(), 23 );
???????? }
??? catch( IOException ioe )
???????? {
?????????? //ioe.printStackTrace();

?????????? exitWithWarning( ioe.toString(), 29 );
???????? }
??? catch( Exception e )
???????? {
?????????? //e.printStackTrace();

?????????? exitWithWarning( e.toString(), 99 );
???????? }
? }

? /*****************************************************************************
?? *
?? * You can change the milliseconds to the date and time string here
?? *
?? * I just return the original
?? *
?? * Don't get the same string :)
?? *
?? ****************************************************************************/
? private final String convertMillisecond2DateTime( long millisecond )
? {
??? return ""+millisecond;
? }

? /*****************************************************************************
?? *
?? * Return the warning and the exit code, then exit the application
?? *
?? ****************************************************************************/
? private final void exitWithWarning( String warning, int code )
? {
??? System.out.println( warning==null ? "" : warning );

??? System.exit( code );
? }

? /*****************************************************************************
?? *
?? * 主函數入口
?? *
?? ****************************************************************************/
? public final static void main( String[] args )
? {
??? SingleInstance si=new SingleInstance( "error", ".txt", "error" );

??? final JFrame frame=new JFrame( "Just single instance. By NeedJava. 2007.08.29" );

??? //I stay here, to make some friends happy.
??? frame.addWindowListener( new WindowAdapter()
??? {
????? public void windowClosing( WindowEvent we )
????? {
??????? frame.dispose();

??????? System.exit( 0 );
????? }
??? } );

??? frame.setBounds( 200, 200, 700, 70 );

??? frame.setVisible( true );
? }
}