persistentecho.java

it contains the practical programs in our college

import java.util.Properties;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class PersistentEcho {
    public static void main (String[] args) {
        String argString = "";
        boolean notProperty = true;

        //Are there arguments? If so retrieve them.
        if (args.length > 0) {
            for (String arg: args) {
                argString += arg + " ";
            }
            argString = argString.trim();
        }
        //No arguments, is there an environment variable? If so,
        //retrieve it.
        else if ((argString = System.getenv("PERSISTENTECHO")) != null) {}
        //No environment variable either. Retrieve property value.
        else {
            notProperty = false;
            //Set argString to null. If it's still null after we exit
            //the try block, we've failed to retrieve the property
            //value.
            argString = null;
            FileInputStream fileInputStream = null;
            try {
                fileInputStream = new FileInputStream("PersistentEcho.txt");
                Properties inProperties = new Properties();
                inProperties.load(fileInputStream);
                argString = inProperties.getProperty("argString");
            } catch (IOException e) {
                System.err.println("Can't read property file.");
                System.exit(1);
            } finally {
                if (fileInputStream != null) {
                    try {
                        fileInputStream.close();
                    } catch(IOException e) {};
                }
            }
        }
        if (argString == null) {
            System.err.println("Couldn't find argString property");
            System.exit(1);
        }

        //Somehow, we got the value. Echo it already!
        System.out.println(argString);

        //If we didn't retrieve the value from the property, save it
        //in the property.
        if (notProperty) {
            Properties outProperties = new Properties();
            outProperties.setProperty("argString", argString);
            FileOutputStream fileOutputStream = null;
            try {
                fileOutputStream = new FileOutputStream("PersistentEcho.txt");
                outProperties.store(fileOutputStream,
                        "PersistentEcho properties");
            } catch (IOException e) {}
            finally {
                if (fileOutputStream != null) {
                    try {
                        fileOutputStream.close();
                    } catch(IOException e) {};
                }
            }
        }
    }
}