loan pattern in java

loanpatternJava

/**
 * This class is an illustration of using loan pattern(a.k.a lender-lendee pattern) 
 * @author prassee
 */
public class IOResourceLender {

  /**
	 * Interface to write data to the buffer. Clients using this
	 * class should provide impl of this interface 
	 * @author sysadmin
	 *
	 */
	public interface WriteBlock {
		void call(BufferedWriter writer) throws IOException;
	}

	/**
	 * Interface to read data from the buffer. Clients using this
	 * class should provide impl of this interface
	 * @author sysadmin
	 *
	 */
	public interface ReadBlock {
		void call(BufferedReader reader) throws IOException;
	}

	/**
	 * method which loans / lends the resource. Here {@link FileWriter} is the 
	 * resource lent. The resource is managed for the given impl of {@link WriteBlock}
	 *  
	 * @param fileName
	 * @param block
	 * @throws IOException
	 */
	public static void writeUsing(String fileName, WriteBlock block)
			throws IOException {
		File csvFile = new File(fileName);
		if (!csvFile.exists()) {
			csvFile.createNewFile();
		}
		FileWriter fw = new FileWriter(csvFile.getAbsoluteFile(), true);
		BufferedWriter bufferedWriter = new BufferedWriter(fw);
		block.call(bufferedWriter);
		bufferedWriter.close();
	}

	/**
	 * method which loans / lends the resource. Here {@link FileReader} is the 
	 * resource lent. The resource is managed for 
	 * the given impl of {@link ReadBlock}
	 *  
	 * @param fileName
	 * @param block
	 * @throws IOException
	 */
	public static void readUsing(String fileName, ReadBlock block)
			throws IOException {
		File inputFile = new File(fileName);
		FileReader fileReader = new FileReader(inputFile.getAbsoluteFile());
		BufferedReader bufferedReader = new BufferedReader(fileReader);
		block.call(bufferedReader);
		bufferedReader.close();
	}
}

// client code 

public void writeColumnNameToMetaFile(final String attrName,
  		String fileName, final String[] colNames) throws IOException {
		IOResourceLender.writeUsing(fileName,
				new IOResourceLender.WriteBlock() {
					public void call(BufferedWriter out) throws IOException {
						StringBuilder buffer = new StringBuilder();
						for (String string : colNames) {
							buffer.append(string);
							buffer.append(",");
						}
						out.append(attrName + " = " + buffer.toString());
						out.newLine();
					}
				});
	}