1.工厂模式
Spring中的应用：
BeanFactory 构造对象
// student.xml
<bean id="studentBean" class="advanced.Student">
<property name="name" value="Tom"/>
<property name="age" value="18"/>
</bean>
public static void main(String[] args) throws Exception {
BeanFactory bf = new ClassPathXmlApplicationContext("student.xml");
Student studentBean = (Student) bf.getBean("studentBean");
studentBean.print();
}
2. 建造者设计模式
建设者设计模式是属于创建对象模式三剑客的第一种模式。该模式用于简化复杂对象的构造。要理解这个概念，想象一个说明程序员简历的对象。在这个对象中，我们想存储个人信息（名字，地址等）以及技术信息（知识语言，已实现的项目等）。该对象的构造可能如下所示：
// with constructor
Programmer programmer = new Programmer("first name", "last name", "address Street 39", "ZIP code", "City", "Country", birthDateObject, new String[] {"Java", "PHP", "Perl", "SQL"}, new String[] {"CRM system", "CMS system for government"});
// or with setters
Programmer programmer = new Programmer();
programmer.setName("first name");
programmer.setLastName("last name");
// ... multiple lines after
programmer.setProjects(new String[] {"CRM system", "CMS system for government"});
应用了建造者模式，可以把对象属性设置过程抽象隐藏，交给内置的建造者去做，这时候创建一个对象看起来像这样：
public class Test {
public static void main(String[] args) {
Person person = new Person.Builder().setIdAndName(123,"shan").setSex("男")
.build();
System.out.println(person);
}
}
public class Person {
private Integer id;
private String name;
private String sex;
public static class Builder{
private Person person;
public Builder(){
person = new Person();
}
public Builder setIdAndName(Integer id,String name){
person.id = id;
person.setName(name);
return this;
}
public Builder setSex(String sex){
person.setSex(sex);
return this;
}
public Person build(){
return person;
}
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
@Override
public String toString() {
return "Person{" +
"id=" + id +
", name='" + name + '\'' +
", sex='" + sex + '\'' +
'}';
}
}
Spring中的应用：
public class BeanDefinitionBuilder {
/**
* The {@code BeanDefinition} instance we are creating.
*/
private AbstractBeanDefinition beanDefinition;
// ... some not important methods for this article
// Some of building methods
/**
* Set the name of the parent definition of this bean definition.
*/
public BeanDefinitionBuilder setParentName(String parentName) {
this.beanDefinition.setParentName(parentName);
return this;
}
/**
* Set the name of the factory method to use for this definition.
*/
public BeanDefinitionBuilder setFactoryMethod(String factoryMethod) {
this.beanDefinition.setFactoryMethodName(factoryMethod);
return this;
}
/**
* Add an indexed constructor arg value. The current index is tracked internally
* and all additions are at the present point.
* @deprecated since Spring 2.5, in favor of {@link #addConstructorArgValue}
*/
@Deprecated
public BeanDefinitionBuilder addConstructorArg(Object value) {
return addConstructorArgValue(value);
}
/**
* Add an indexed constructor arg value. The current index is tracked internally
* and all additions are at the present point.
*/
public BeanDefinitionBuilder addConstructorArgValue(Object value) {
this.beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(
this.constructorArgIndex++, value);
return this;
}
/**
* Add a reference to a named bean as a constructor arg.
* @see #addConstructorArgValue(Object)
*/
public BeanDefinitionBuilder addConstructorArgReference(String beanName) {
this.beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(
this.constructorArgIndex++, new RuntimeBeanReference(beanName));
return this;
}
/**
* Add the supplied property value under the given name.
*/
public BeanDefinitionBuilder addPropertyValue(String name, Object value) {
this.beanDefinition.getPropertyValues().add(name, value);
return this;
}
/**
* Add a reference to the specified bean name under the property specified.
* @param name the name of the property to add the reference to
* @param beanName the name of the bean being referenced
*/
public BeanDefinitionBuilder addPropertyReference(String name, String beanName) {
this.beanDefinition.getPropertyValues().add(name, new RuntimeBeanReference(beanName));
return this;
}
/**
* Set the init method for this definition.
*/
public BeanDefinitionBuilder setInitMethodName(String methodName) {
this.beanDefinition.setInitMethodName(methodName);
return this;
}
// Methods that can be used to construct BeanDefinition
/**
* Return the current BeanDefinition object in its raw (unvalidated) form.
* @see #getBeanDefinition()
*/
public AbstractBeanDefinition getRawBeanDefinition() {
return this.beanDefinition;
}
/**
* Validate and return the created BeanDefinition object.
*/
public AbstractBeanDefinition getBeanDefinition() {
this.beanDefinition.validate();
return this.beanDefinition;
}
}
3. 装饰者模式
装饰模式的核心在于抽象装饰类的设计，其典型代码如下所示：
class Decorator implements Component{
private Component component; //维持一个对抽象构件对象的引用
public Decorator(Component component) { //注入一个抽象构件类型的对象
this.component=component;
}
public void operation(){
component.operation(); //调用原有业务方法
}
}
在抽象装饰类Decorator中定义了一个Component类型的对象component，维持一个对抽象构件对象的引用，并可以通过构造方法或Setter方法将一个Component类型的对象注入进来，同时由于Decorator类实现了抽象构件Component接口，因此需要实现在其中声明的业务方法operation()，需要注意的是在Decorator中并未真正实现operation()方法，而只是调用原有component对象的operation()方法，它没有真正实施装饰，而是提供一个统一的接口，将具体装饰过程交给子类完成。
在Decorator的子类即具体装饰类中将继承operation()方法并根据需要进行扩展，典型的具体装饰类代码如下：
class ConcreteDecorator extends Decorator{
// 构造注入
public ConcreteDecorator(Component component){
super(component);
}
public void operation() {
super.operation(); //调用原有业务方法
addedBehavior(); //调用新增业务方法
}
//新增业务方法
public void addedBehavior(){
……
}
}
Java I/O 使用了装饰者模式来实现。以 InputStream 为例，
- InputStream 是抽象组件；
- FileInputStream 是 InputStream 的子类，属于具体组件，提供了字节流的输入操作；
- FilterInputStream 属于抽象装饰者，装饰者用于装饰组件，为组件提供额外的功能。例如 BufferedInputStream 为 FileInputStream 提供缓存的功能。
实例化一个具有缓存功能的字节流对象时，只需要在 FileInputStream 对象上再套一层 BufferedInputStream 对象即可。
FileInputStream fileInputStream = new FileInputStream(filePath);
BufferedInputStream bufferedInputStream = new BufferedInputStream(fileInputStream);
DataInputStream 装饰者提供了对更多数据类型进行输入的操作，比如 int、double 等基本类型。
移步查看装饰者模式：学好设计模式防被祭天：装饰者模式
设计模式详解——装饰者模式
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