Command java

Examples of Command Design Pattern

Command Pattern Receivers

package edu.redwoods.command;

public interface FileSystemReceiver {

    void openFile();
    void writeFile();
    void closeFile();
}

package edu.redwoods.command;

public class UnixFileSystemReceiver implements FileSystemReceiver {

    @Override
    public void openFile() {
        System.out.println("Opening file in unix OS");
    }

    @Override
    public void writeFile() {
        System.out.println("Writing file in unix OS");
    }

    @Override
    public void closeFile() {
        System.out.println("Closing file in unix OS");
    }

}

package edu.redwoods.command;

public class WindowsFileSystemReceiver implements FileSystemReceiver {

    @Override
    public void openFile() {
        System.out.println("Opening file in Windows OS");

    }

    @Override
    public void writeFile() {
        System.out.println("Writing file in Windows OS");
    }

    @Override
    public void closeFile() {
        System.out.println("Closing file in Windows OS");
    }

}

Command Pattern Interface and Concrete Implementations

package edu.redwoods.command;

public interface Command {

    void execute();
}

package edu.redwoods.command;

public class OpenFileCommand implements Command {

    private FileSystemReceiver fileSystem;

    public OpenFileCommand(FileSystemReceiver fs){
        this.fileSystem=fs;
    }
    @Override
    public void execute() {
        //open command is forwarding request to openFile method
        this.fileSystem.openFile();
    }

}

package edu.redwoods.command;

public class CloseFileCommand implements Command {

    private FileSystemReceiver fileSystem;

    public CloseFileCommand(FileSystemReceiver fs){
        this.fileSystem=fs;
    }
    @Override
    public void execute() {
        this.fileSystem.closeFile();
    }

}

package edu.redwoods.command;

public class WriteFileCommand implements Command {

    private FileSystemReceiver fileSystem;

    public WriteFileCommand(FileSystemReceiver fs){
        this.fileSystem=fs;
    }
    @Override
    public void execute() {
        this.fileSystem.writeFile();
    }

}

Command Pattern Invoker

package edu.redwoods.command;

public class FileInvoker {

    public Command command;

    public FileInvoker(Command c){
        this.command=c;
    }

    public void execute(){
        this.command.execute();
    }
}

Utility to Determine Proper OS (Factory Method Anyone!?!)

package edu.redwoods.command;

public class FileSystemReceiverUtil {

    public static FileSystemReceiver getUnderlyingFileSystem(){
         String osName = System.getProperty("os.name");
         System.out.println("Underlying OS is:"+osName);
         if(osName.contains("Windows")){
             return new WindowsFileSystemReceiver();
         }else{
             return new UnixFileSystemReceiver();
         }
    }

}

Client for Command Design Pattern

package edu.redwoods.command;

public class FileSystemClient {

    public static void main(String[] args) {
        //Creating the receiver object
        FileSystemReceiver fs = FileSystemReceiverUtil.getUnderlyingFileSystem();

        //creating command and associating with receiver
        OpenFileCommand openFileCommand = new OpenFileCommand(fs);

        //Creating invoker and associating with Command
        FileInvoker file = new FileInvoker(openFileCommand);

        //perform action on invoker object
        file.execute();

        WriteFileCommand writeFileCommand = new WriteFileCommand(fs);
        file = new FileInvoker(writeFileCommand);
        file.execute();

        CloseFileCommand closeFileCommand = new CloseFileCommand(fs);
        file = new FileInvoker(closeFileCommand);
        file.execute();
    }

}