Design Pattern 简明教程

Design Patterns - Composite Entity Pattern

复合实体模式用于 EJB 持久性机制。复合实体是一个 EJB 实体 Bean，它表示一个对象图。当更新复合实体时，由 EJB 实体 Bean 管理的内部相关对象 Bean 会自动得到更新。下面是复合实体 Bean 中的参与者。

Composite Entity pattern is used in EJB persistence mechanism. A Composite entity is an EJB entity bean which represents a graph of objects. When a composite entity is updated, internally dependent objects beans get updated automatically as being managed by EJB entity bean. Following are the participants in Composite Entity Bean.

Composite Entity - It is primary entity bean. It can be coarse grained or can contain a coarse grained object to be used for persistence purpose.
Coarse-Grained Object - This object contains dependent objects. It has its own life cycle and also manages life cycle of dependent objects.
Dependent Object - Dependent object is an object which depends on coarse grained object for its persistence lifecycle.
Strategies - Strategies represents how to implement a Composite Entity.

Implementation

我们将创建充当 CompositeEntity 的 CompositeEntity 对象。CoarseGrainedObject 将是一个包含从属对象的对象。我们的演示类 CompositeEntityPatternDemo 将使用 Client 类来演示复合实体模式的使用。

We are going to create CompositeEntity object acting as CompositeEntity. CoarseGrainedObject will be a class which contains dependent objects. CompositeEntityPatternDemo, our demo class will use Client class to demonstrate use of Composite Entity pattern.

Step 1

创建相关对象。

Create Dependent Objects.

DependentObject1.java

public class DependentObject1 {

   private String data;

   public void setData(String data){
      this.data = data;
   }

   public String getData(){
      return data;
   }
}

DependentObject2.java

public class DependentObject2 {

   private String data;

   public void setData(String data){
      this.data = data;
   }

   public String getData(){
      return data;
   }
}

Step 2

创建粗粒度对象。

Create Coarse Grained Object.

CoarseGrainedObject.java

public class CoarseGrainedObject {
   DependentObject1 do1 = new DependentObject1();
   DependentObject2 do2 = new DependentObject2();

   public void setData(String data1, String data2){
      do1.setData(data1);
      do2.setData(data2);
   }

   public String[] getData(){
      return new String[] {do1.getData(),do2.getData()};
   }
}

Step 3

创建复合实体。

Create Composite Entity.

CompositeEntity.java

public class CompositeEntity {
   private CoarseGrainedObject cgo = new CoarseGrainedObject();

   public void setData(String data1, String data2){
      cgo.setData(data1, data2);
   }

   public String[] getData(){
      return cgo.getData();
   }
}

Step 4

创建客户端类以使用复合实体。

Create Client class to use Composite Entity.

Client.java

public class Client {
   private CompositeEntity compositeEntity = new CompositeEntity();

   public void printData(){

      for (int i = 0; i < compositeEntity.getData().length; i++) {
         System.out.println("Data: " + compositeEntity.getData()[i]);
      }
   }

   public void setData(String data1, String data2){
      compositeEntity.setData(data1, data2);
   }
}

Step 5

使用 Client 来演示 Composite Entity 设计模式用法。

Use the Client to demonstrate Composite Entity design pattern usage.

CompositeEntityPatternDemo.java

public class CompositeEntityPatternDemo {
   public static void main(String[] args) {

       Client client = new Client();
       client.setData("Test", "Data");
       client.printData();
       client.setData("Second Test", "Data1");
       client.printData();
   }
}

Step 6

验证输出。

Verify the output.

Data: Test
Data: Data
Data: Second Test
Data: Data1