// CommandExample.java

import java.util.HashMap;

// ************************************************************************
/**
 * CommandExample.java
 *
 * Provides a simple Command Design Pattern Example.
 *
 * The example will show how to use the Command Design Pattern
 * by replacing conditional control logic in a simulated M-V-C Model
 * 2 servlet. So as not to need a webserver to implement this
 * example, a phamtom object will be created and passed in for
 * demonstration purposes.
*/
// ************************************************************************
public class CommandExample {
	public static void main(String[] args) {
		CommandExample.log(1,"Begin Command Design Pattern example.");
		ExampleServlet exampleServlet = new ExampleServlet();
		int maxApproaches = 3;
		String exampleActionRequest = "update";

		CommandExample.log(1,"Simulated servlet request received is: " +
			exampleActionRequest);
		CommandExample.log(1,"Code will show " + maxApproaches +
			" approaches as to how such a command can be processed.");
		for(int i=1; i<=maxApproaches; i++) {
			exampleServlet.doPost(i,exampleActionRequest);
		} //endfor
		CommandExample.log(1,"End Command Design Pattern example.");
	} //endmain

	// ===================================================================
	public static void log(int aLevel, String aMsg) {
		boolean showLogTraceToSystemOut = true;
	  	if(showLogTraceToSystemOut) {
			String prefix = "";
		  	if(aLevel == 1) {
				prefix = "   ---> ";
		  	} else if(aLevel == 2) {
				prefix = "     ---> ";
		  	} else if(aLevel == 3) {
				prefix = "       ---> ";
		  	} //endif
		  	System.out.println(prefix + aMsg);
	  	} //endif
  	} //endmethod: log
} //endclass: CommandExample.java



// ************************************************************************
/**
 * ExampleServlet.java
 *
 * Simulates a servlet in an M-V-C Model 2 environment.
 *
 * @param action the desired action the servlet is to perform.
*/
// ************************************************************************
class ExampleServlet  {
	private HashMap commandMap = new HashMap();

	// ===================================================================
	public ExampleServlet() {
		//-- Initialize HashMap of possible ActionType concrete objects
		commandMap.put("create", new ActionTypeCreate());
		commandMap.put("replace", new ActionTypeReplace());
		commandMap.put("update", new ActionTypeUpdate());
		commandMap.put("delete", new ActionTypeDelete());
	} //endmain

	// ===================================================================
	public void doPost(int approachSolution, String action) {
		switch (approachSolution) {
		case 1:
			CommandExample.log(2,
			"Demonstrating from full conditional processing.");
			performTask1(action);
			break;
		case 2:
			CommandExample.log(2,
			"Demonstrating from abstracted concrete class processing.");
			performTask2(action);
			break;
		case 3:
			CommandExample.log(2,
			"Demonstrating from Command Design Pattern processing.");
			performTask3(action);
			break;
		} //endswitch


	} //endmethod: doPost

	// ===================================================================
	private void performTask1(String action) {
		//-- Process business logic within conditional statements
		if( action.equalsIgnoreCase("create") ) {
			CommandExample.log(3,
				"create business logic executing...");
		} else if( action.equalsIgnoreCase("replace") ) {
			CommandExample.log(3,
				"replace business logic executing...");
		} else if( action.equalsIgnoreCase("update") ) {
			CommandExample.log(3,
				"update business logic executing...");
		} else if( action.equalsIgnoreCase("delete") ) {
			CommandExample.log(3,
				"delete business logic executing...");
		} //endif
	} //endmethod: performTask1

	// ===================================================================
	private void performTask2(String action) {
		//-- Abstracts out all business logic into separate classes
		ActionType cmd = null;

		if( action.equalsIgnoreCase("create") ) {
			cmd = new ActionTypeCreate();
		} else if( action.equalsIgnoreCase("replace") ) {
			cmd = new ActionTypeReplace();
		} else if( action.equalsIgnoreCase("update") ) {
			cmd = new ActionTypeUpdate();
		} else if( action.equalsIgnoreCase("delete") ) {
			cmd = new ActionTypeDelete();
		} //endif
		cmd.execute();
	} //endmethod: performTask2

	// ===================================================================
	private void performTask3(String action) {
		//-- Uses the Command Design Pattern to polymorphically
		//-- execute desired action
		ActionType cmd = (ActionType)commandMap.get(action);
		cmd.execute();
	} //endmethod: performTask3
} //endclass: ExampleServlet


// ************************************************************************
abstract class ActionType {
	abstract public void execute();
} //endclass: ActionType

// ************************************************************************
class ActionTypeCreate extends ActionType {
	public void execute() {
		CommandExample.log(3,
			"ActionTypeCreate business logic executing...");
	} //endmethod: execute
} //endclass: ActionTypeCreate

// ************************************************************************
class ActionTypeReplace extends ActionType {
	public void execute() {
		CommandExample.log(3,
			"ActionTypeReplace business logic executing...");
	} //endmethod: execute
} //endclass: ActionTypeReplace

// ************************************************************************
class ActionTypeUpdate extends ActionType {
	public void execute() {
		CommandExample.log(3,
			"ActionTypeUpdate business logic executing...");
	} //endmethod: execute
} //endclass: ActionTypeUpdate

// ************************************************************************
class ActionTypeDelete extends ActionType {
	public void execute() {
		CommandExample.log(3,
			"ActionTypeDelete business logic executing...");
	} //endmethod: execute
} //endclass: ActionTypeDelete