Java Code Samples

Check Null ======> System.out.println( "actualValue ======> " + ( (actualValue != null)? actualValue: "NULL") );

Dynamically Getting parameters from a property file:
A Value in Property File:
FILE_NAME = ABC-rpt_{0}_{1}_WXD_{2}.out

How to populate FILE_NAME dynamically in Java:

Object[] args = {"Frank","Wang","2011-07-10"};
theFileName = PropertyFileHandler.getInstance().getProperty("FILE_NAME",args);

import java.io.InputStream;
import java.text.MessageFormat;
import java.util.Properties;
import org.apache.log4j.Logger;

public class PropertyFileHandler
{
private static final PropertyFileHandler instance = new PropertyFileHandler();
private static final String PROPERTY_PATH = "/myPropertyFile.properties";
private static final Logger log = Logger.getLogger(PropertyFileHandler.class);

private Properties props;

private PropertyFileHandler()
{
props = new Properties();
InputStream inputStream = getClass.getResourceAsStream(PROPERTY_PATH);

try {
props.load(inputStream);
}
catch(IOException ex) {
log.error( ex.getMessage() );
}
}

private PrppertyFileHandler(String filePath)
{
props = new Properties();
FileInputStream fileInputStream = getClass.getResourceAsStream(filePath);

try {
props.load(fileInputStream);
}
catch(IOException ex) {
log.error( ex.getMessage() );
}
}

private PrppertyFileHandler(Properties preperties)
{
props = properties;
}

public static PropertyFileHandler getInstance()
{
return instance;
}

public String getProperty(String propertyKey, Object[] args)
{
String theResult = "";

try {
theResult = props.getProperty(propertyKey);
theResult = MessageFormat.format( theResult, args);
}
catch(Exception ex) {
{ log.error( ex.getMessage() );
}

return theResult;
}

} //end of class


UNIX Commands

To see my current directory:

$ pwd

$ ls -l

$ mkdir input

Change mode to a directory to [write permitted]:
$ sudo chmod 777 /home/usr/frank

To Change Directory:

$ cd ..

$ cd opt/frank/input
To display the users currently logged in:

$ who

To see current login user name:

$ who am i

Dynamically monitor a log file in UNIX:

$ tail -f system.out

Copy files to upper directory:

$ cp *.* ..

Copy files to a directory:

$ cp *.* /home/devuser/frank

Search a file for a pattern (e.g.: looking for a file in which String "sue" is contained in it):

$ grep sue temp
Display contents of a file:

$ cat myfile
Move files (from one location to another. e.g.: move 3 files --- section1, section2, section3 --- to the sub-directory called Chapter1):

$ mv section1 section2 section3 Chapter1

$ mv sec* Ch*1
Find Files (e.g: search the entire system for files whose names contain String "data" in them):

$ / find -name "*data*" -print

$ find -mtime -6 ===> get all files that were modified within 6 days

Remove / Delete Files (remove/delete all files in current directory):
$ rm *

$ rm *.docx

$ rm -i * ===> prints the name of each file and waits for your response before deleting it.

Remove/Delete a directory:
$ rm -r /home/usr/temp

Remove Files that were modified within 6 days:

$ find -mtime -6 -exec rm -f {} \
Edit a File:

vi filename

a --- append mode
x --- delete mode
[ESC] key --- escape from current mode

:q! --- quit without saving

:wq! --- quit and save changes

Parser:
try
{
BufferedReader reader = new BufferedRead( new InputStreamReader( new FileInputStream("C:\\TEMP\\data.csv") ) );
String workStr = "";

while( (workStr = reader.readLine()) != null )
{
workStr.trim();
}
catch( FileNotFoundException ex ) {
...... }

 

Generator:

try {

    PrintWrintWriter  writer = new PrintWriter( new FileOutputStream( output_filePath ) );

   writer.write( outputStringBuffer.toString );

   writer.close();

}

catch(  IOException ex ) {

   ......

}

 
Zip / un-zip a JAR file:

$ jar -cvf myJarFile.jar *.*

$ jar -xvf myJarFile.jar

Database BLOB issue:
Connection conn = DBConnection.getConnection();

PreparedStatement pstmt = null;
String filename = "index.dat";
String input_blob_file_path = "C:/TEMP/" + filename;
String output_blob_file_path = "C:/DATA/" + filename;
int MAX_BYTE_ARRAY_SIZE = 30720;
int sizeOfBlobFile = 16360;

// insert BLOB data into database table:
try {
pstmt = conn.prepareStatement( "insert into TABLE2(id, file_name, blob_size, blob_data, is_valid_flag, create_user, update_user)" +
+ " values(ATTACHMENT_SEQ.NEXTVAL, ?,?,?,?,?,?)" );

pstmt.setString(1, filename);
pstmt.setString(2, sizeOfBlobFile);

File blobFile = new File( input_blob_file_path );
FileInputStream fileInputStream = new FileInputStream( blobFile );
pstmt.setBinaryStream(3, fileInputStream, (int) blobFile.length() );

pstmt.setString( 4, "true" );
pstmt.setString( 5, "Frank Wang" );
pstmt.setString( 6, Frank Wang" );

pstmt.execute();
pstmt.close();
}
catch(Exception ex) {
...... }


// select BLOB data from database table:
//
InputStream blobFile_inputStream = null;
int current_row_number = 0;

try {
Statement stmt = conn.createStatement();

ResultSet resultSet = stmt.executeQuery( "select max(ID) from TABLE2" );
if( resultSet.next() ) {
current_row_number = resultSet.getInt( 1 );
}
resultSet.close();

ResultSet resultSet2 = stmt.execute( "select BLOB_DATA from TABLE2 where id = " + current_row_number );

while( resultSet2.next() ) {
java.sql.Blob blobData = resultSet2.getBlob( "BLOB_DATA" );
blobFile_inputStream = blobData.getBinaryStream();
}
resultSet2.close();
stmt.close();

FileOutputStream fileOutputStream = new FileOutputStream( output_blob_file_path );
PrintWriter writer = new PrintWriter( fileOutputStream );
byte byteArray[] = new byte[MAX_BYTE_ARRAY_SIZE];

int index = blobFile_inputStream.read( byteArray, 0, MAX_BYTE_ARRAY_SIZE );

while( index != -1 )
{
fileOutputStream.write( byteArray, 0, index );
index = blobFile_inputStream.read( byteArray, 0, MAX_BYTE_ARRAY_SIZE );
}
fileOutputStream.flush();
writer.flush();
writer.close();

}
catch(Exception ex) {
ex.printStackTrace();
}

How to convert a Base64Encoded-String to a file? To save a Binary-String as a File, Always convert it to [InputStream] first!!

1. fileContentByte[] = Base64Decoder.decodeBuffer(inputBinaryString);
2. InputStream inputStream = new ByteArrayInputStream( fileContentByte[] );
3. Where to save:
FileOutputStream outputStream = new FileOutputStream( filePath_for_output );
4. Write the content to the file and save it:
byte[] buffer = new byte[4*1024] ;
int bytesRead = 0;
while( (bytesRead = inputStream.read(buffer)) != -1 ) {
outputStream.write( buffer, 0, bytesRead);
}
outputStream.flush();
inputStream.close();
outputstream.close();

Performance Evaluation:

long  startTime = System.currentTimeMillis();

....................

long  endTime = System.currentTimeMillis();

System.out.println( "Process time = " + (endTime - startTime) );

 

 

GIT Commands:

 

Create a working copy of a local repository:

$ git clone /path/to/repository

$ git clone username@host:/path/to/repository

 

Create a new branch:

$ git branch my_new_branch/dev

 

Create or switch to a new branch:

$ git checkout -b feature/frank

 

Setup a branch to tract the remote branch 'develop' from 'origin':

$ git branch --set-upstream-to=origin/develop

 

Commit changes to a branch:

$ git commit -a -m "feature frank OK"

 

Push all changes to branch:

$ git push origin HEAD

 

Others:

$ git status

$ git switch origin/frank-dev

$ git pull --rebase

 

Java Enum Sample Code