1.Summary
This article is about Facade Design Pattern, this pattern is usually used to handle requests which have a common feature or can be implemented by the same entrance.
First of all, let’s see a picture of Facade Design Pattern which was drawn before through MindNode.app:
2.The example in Java
The biggest feature of Facade pattern is that there is a key-door waiting to handle the requests. The main handler class is called Facade.java and it has a method called public void handleRequest(EntryInfo entryInfo), we will use this method to play the role of doorman who will handle all the requests received.
Now, let see the codes of this method in Facade.java:
public void handleRequest(EntryInfo entryInfo) {
//Facade Pattern Example
try {
entryMap.get(entryInfo.getCity()).enter(entryInfo);
} catch (Exception e) {
this.printError("Sorry, we can NOT handle " + entryInfo.getCity() + "’s cargos for now.");
}
}
See? All the requests are handled by entryMap.get(entryInfo.getCity()).enter(entryInfo), so, what happened in the entryMap?
The codes of entryMap’s initialization:
private static Map<String,IEntry> entryMap = null;
static {
entryMap = new HashMap<String,IEntry>();
entryMap.put("Beijing", new EntryBeijingImpl());
entryMap.put("Shanghai", new EntryShanghaiImpl());
entryMap.put("Guangzhou", new EntryGuangzhouImpl());
entryMap.put("Shenzhen", new EntryShenzhenImpl());
}
In this map, we put some key-values in it. The key is identified by a city’s name, the value is a certain implementation of interface IEntry.
We have interface IEntry looks like this:
package org.acttos.pattern.facade.entry;
import org.acttos.pattern.facade.entry.domain.EntryInfo;
/**
* @author <a href="mailto:[email protected]">Acttos</a>
* @version 1.0.0
*/
public interface IEntry {
public void enter(EntryInfo entryInfo);
}
There is only method called public void enter(EntryInfo entryInfo) in this interface which needs to be implemented by the classes which do the real job.
We have EntryBeijingImpl.java,EntryShanghaiImpl.java,EntryGuangzhouImpl.java and EntryShenzhenImpl.java to handle the request (Here is EntryInfo).
One of the implementation of the interface IEntry can be on behalf of all theothers, here let’s see EntryBeijingImpl.java:
public class EntryBeijingImpl implements IEntry {
/* (non-Javadoc)
* @see org.acttos.pattern.facade.entry.IEntry#enter(org.acttos.pattern.facade.entry.domain.EntryInfo)
*/
@Override
public void enter(EntryInfo entryInfo) {
System.out.println("I am Beijing Entry handler, I received a cargo '" + entryInfo.getCargo() + "'.");
}
}
We just print out the message with different cargos in all the EntryXxxxImpl.java files. In fact, we will do the different things in every implementation class of IEntry, that is the meaning of Facade:
“Do different things through only one key-door”.
Then, we need to take a look at class EntryInfo:
public class EntryInfo {
private String city;
private String cargo;
/**
* @return the city
*/
public String getCity() {
return city;
}
/**
* @param city the city to set
*/
public void setCity(String city) {
this.city = city;
}
/**
* @return the cargo
*/
public String getCargo() {
return cargo;
}
/**
* @param cargo the cargo to set
*/
public void setCargo(String cargo) {
this.cargo = cargo;
}
}
Here EntryInfo.java is just a pojo(plain old java object) which has some properties, we also need to design the much more complecated request class in real job.
Now, let’s finish the main method in Facade.java:
public static void main(String[] args) {
Facade facade = new Facade();
EntryInfo entryInfo = new EntryInfo();
entryInfo.setCity("Beijing");
entryInfo.setCargo("Cargo for " + entryInfo.getCity());
facade.handleRequest(entryInfo);
entryInfo.setCity("Shanghai");
entryInfo.setCargo("Cargo for " + entryInfo.getCity());
facade.handleRequest(entryInfo);
entryInfo.setCity("Guangzhou");
entryInfo.setCargo("Cargo for " + entryInfo.getCity());
facade.handleRequest(entryInfo);
entryInfo.setCity("Shenzhen");
entryInfo.setCargo("Cargo for " + entryInfo.getCity());
facade.handleRequest(entryInfo);
entryInfo.setCity("Nanjing");
entryInfo.setCargo("Cargo for " + entryInfo.getCity());
facade.handleRequest(entryInfo);
}
When we execute Facade.java as Java application, we will get the output mostly like this:
I am Beijing Entry handler, I received a cargo 'Cargo for Beijing'.
I am Shanghai Entry handler, I received a cargo 'Cargo for Shanghai'.
I am Guangzhou Entry handler, I received a cargo 'Cargo for Guangzhou'.
I am Shenzhen Entry handler, I received a cargo 'Cargo for Shenzhen'.
========== ERROR ==========
Sorry, we can NOT handle Nanjing’s cargos for now.
========== ERROR ==========
Maybe you could’t understand the codes above clearly, because these codes are just part of Java project Design Pattern or my poor English can not bring my real idears in heart. Fortunately, You can find the completed codes [ Here ], and figure it out by your self.
3.Thanks for visiting.
Good day and see you later!
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