Builder设计模式例子

Effective java 2中例子：

当构造函数中的参数很多，且只有少数为必须设置值时，可以使用Builder模式。

 

public class NutritionFacts {
	private final int servingSize;
	private final int servings;
	private final int calories;
	private final int fat;
	private final int sodium;
	private final int carbohydrate;

	public static class Builder {
		// Required parameters
		private final int servingSize;
		private final int servings;
		// Optional parameters - initialized to default values
		private int calories = 0;
		private int fat = 0;
		private int carbohydrate = 0;
		private int sodium = 0;

		public Builder(int servingSize, int servings) {
			this.servingSize = servingSize;
			this.servings = servings;
		}

		public Builder calories(int val) {
			calories = val;
			return this;
		}

		public Builder fat(int val) {
			fat = val;
			return this;
		}

		public Builder carbohydrate(int val) {
			carbohydrate = val;
			return this;
		}

		public Builder sodium(int val) {
			sodium = val;
			return this;
		}

		public NutritionFacts build() {
			return new NutritionFacts(this);
		}
	}

	private NutritionFacts(Builder builder) {
		servingSize = builder.servingSize;
		servings = builder.servings;
		calories = builder.calories;
		fat = builder.fat;
		sodium = builder.sodium;
		carbohydrate = builder.carbohydrate;
	}
}

 调用方式：

 

		NutritionFacts cocaCola = new NutritionFacts.Builder(240, 8)
				.calories(100).sodium(35).carbohydrate(27).build();

 

 

Spring中例子：

  BeanDefinitionBuilder 构建 Builder 实例后，设置对应值，最后通过 getBeanDefinition 方法，获取需要的实例，获取方法中有实例必要参数是否设置的检查，保证获取的实例是合法的。

/**
 * Programmatic means of constructing
 * {@link org.springframework.beans.factory.config.BeanDefinition BeanDefinitions}
 * using the builder pattern. Intended primarily for use when implementing Spring 2.0
 * {@link org.springframework.beans.factory.xml.NamespaceHandler NamespaceHandlers}.
 *
 * @author Rod Johnson
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @since 2.0
 */
public class BeanDefinitionBuilder  {

	/**
	 * Create a new <code>BeanDefinitionBuilder</code> used to construct a {@link GenericBeanDefinition}.
	 */
	public static BeanDefinitionBuilder genericBeanDefinition() {
		BeanDefinitionBuilder builder = new BeanDefinitionBuilder();
		builder.beanDefinition = new GenericBeanDefinition();
		return builder;
	}

	/**
	 * Create a new <code>BeanDefinitionBuilder</code> used to construct a {@link GenericBeanDefinition}.
	 * @param beanClass the <code>Class</code> of the bean that the definition is being created for
	 */
	public static BeanDefinitionBuilder genericBeanDefinition(Class beanClass) {
		BeanDefinitionBuilder builder = new BeanDefinitionBuilder();
		builder.beanDefinition = new GenericBeanDefinition();
		builder.beanDefinition.setBeanClass(beanClass);
		return builder;
	}

	/**
	 * Create a new <code>BeanDefinitionBuilder</code> used to construct a {@link GenericBeanDefinition}.
	 * @param beanClassName the class name for the bean that the definition is being created for
	 */
	public static BeanDefinitionBuilder genericBeanDefinition(String beanClassName) {
		BeanDefinitionBuilder builder = new BeanDefinitionBuilder();
		builder.beanDefinition = new GenericBeanDefinition();
		builder.beanDefinition.setBeanClassName(beanClassName);
		return builder;
	}

	/**
	 * Create a new <code>BeanDefinitionBuilder</code> used to construct a {@link RootBeanDefinition}.
	 * @param beanClass the <code>Class</code> of the bean that the definition is being created for
	 */
	public static BeanDefinitionBuilder rootBeanDefinition(Class beanClass) {
		return rootBeanDefinition(beanClass, null);
	}

	/**
	 * Create a new <code>BeanDefinitionBuilder</code> used to construct a {@link RootBeanDefinition}.
	 * @param beanClass the <code>Class</code> of the bean that the definition is being created for
	 * @param factoryMethodName the name of the method to use to construct the bean instance
	 */
	public static BeanDefinitionBuilder rootBeanDefinition(Class beanClass, String factoryMethodName) {
		BeanDefinitionBuilder builder = new BeanDefinitionBuilder();
		builder.beanDefinition = new RootBeanDefinition();
		builder.beanDefinition.setBeanClass(beanClass);
		builder.beanDefinition.setFactoryMethodName(factoryMethodName);
		return builder;
	}

	/**
	 * Create a new <code>BeanDefinitionBuilder</code> used to construct a {@link RootBeanDefinition}.
	 * @param beanClassName the class name for the bean that the definition is being created for
	 */
	public static BeanDefinitionBuilder rootBeanDefinition(String beanClassName) {
		return rootBeanDefinition(beanClassName, null);
	}

	/**
	 * Create a new <code>BeanDefinitionBuilder</code> used to construct a {@link RootBeanDefinition}.
	 * @param beanClassName the class name for the bean that the definition is being created for
	 * @param factoryMethodName the name of the method to use to construct the bean instance
	 */
	public static BeanDefinitionBuilder rootBeanDefinition(String beanClassName, String factoryMethodName) {
		BeanDefinitionBuilder builder = new BeanDefinitionBuilder();
		builder.beanDefinition = new RootBeanDefinition();
		builder.beanDefinition.setBeanClassName(beanClassName);
		builder.beanDefinition.setFactoryMethodName(factoryMethodName);
		return builder;
	}

	/**
	 * Create a new <code>BeanDefinitionBuilder</code> used to construct a {@link ChildBeanDefinition}.
	 * @param parentName the name of the parent bean
	 */
	public static BeanDefinitionBuilder childBeanDefinition(String parentName) {
		BeanDefinitionBuilder builder = new BeanDefinitionBuilder();
		builder.beanDefinition = new ChildBeanDefinition(parentName);
		return builder;
	}


	/**
	 * The <code>BeanDefinition</code> instance we are creating.
	 */
	private AbstractBeanDefinition beanDefinition;

	/**
	 * Our current position with respect to constructor args.
	 */
	private int constructorArgIndex;


	/**
	 * Enforce the use of factory methods.
	 */
	private BeanDefinitionBuilder() {
	}

	/**
	 * 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;
	}


	/**
	 * 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;
	}

	/**
	 * Set the name of the factory bean to use for this definition.
	 * @deprecated since Spring 2.5, in favor of preparing this on the
	 * {@link #getRawBeanDefinition() raw BeanDefinition object}
	 */
	@Deprecated
	public BeanDefinitionBuilder setFactoryBean(String factoryBean, String factoryMethod) {
		this.beanDefinition.setFactoryBeanName(factoryBean);
		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;
	}

	/**
	 * Set the destroy method for this definition.
	 */
	public BeanDefinitionBuilder setDestroyMethodName(String methodName) {
		this.beanDefinition.setDestroyMethodName(methodName);
		return this;
	}


	/**
	 * Set the scope of this definition.
	 * @see org.springframework.beans.factory.config.BeanDefinition#SCOPE_SINGLETON
	 * @see org.springframework.beans.factory.config.BeanDefinition#SCOPE_PROTOTYPE
	 */
	public BeanDefinitionBuilder setScope(String scope) {
		this.beanDefinition.setScope(scope);
		return this;
	}

	/**
	 * Set whether or not this definition describes a singleton bean,
	 * as alternative to {@link #setScope}.
	 * @deprecated since Spring 2.5, in favor of {@link #setScope}
	 */
	@Deprecated
	public BeanDefinitionBuilder setSingleton(boolean singleton) {
		this.beanDefinition.setSingleton(singleton);
		return this;
	}

	/**
	 * Set whether or not this definition is abstract.
	 */
	public BeanDefinitionBuilder setAbstract(boolean flag) {
		this.beanDefinition.setAbstract(flag);
		return this;
	}

	/**
	 * Set whether beans for this definition should be lazily initialized or not.
	 */
	public BeanDefinitionBuilder setLazyInit(boolean lazy) {
		this.beanDefinition.setLazyInit(lazy);
		return this;
	}

	/**
	 * Set the autowire mode for this definition.
	 */
	public BeanDefinitionBuilder setAutowireMode(int autowireMode) {
		beanDefinition.setAutowireMode(autowireMode);
		return this;
	}

	/**
	 * Set the depency check mode for this definition.
	 */
	public BeanDefinitionBuilder setDependencyCheck(int dependencyCheck) {
		beanDefinition.setDependencyCheck(dependencyCheck);
		return this;
	}

	/**
	 * Append the specified bean name to the list of beans that this definition
	 * depends on.
	 */
	public BeanDefinitionBuilder addDependsOn(String beanName) {
		if (this.beanDefinition.getDependsOn() == null) {
			this.beanDefinition.setDependsOn(new String[] {beanName});
		}
		else {
			String[] added = (String[]) ObjectUtils.addObjectToArray(this.beanDefinition.getDependsOn(), beanName);
			this.beanDefinition.setDependsOn(added);
		}
		return this;
	}

	/**
	 * Set the role of this definition.
	 */
	public BeanDefinitionBuilder setRole(int role) {
		this.beanDefinition.setRole(role);
		return this;
	}

	/**
	 * Set the source of this definition.
	 * @deprecated since Spring 2.5, in favor of preparing this on the
	 * {@link #getRawBeanDefinition() raw BeanDefinition object}
	 */
	@Deprecated
	public BeanDefinitionBuilder setSource(Object source) {
		this.beanDefinition.setSource(source);
		return this;
	}

	/**
	 * Set the description associated with this definition.
	 * @deprecated since Spring 2.5, in favor of preparing this on the
	 * {@link #getRawBeanDefinition() raw BeanDefinition object}
	 */
	@Deprecated
	public BeanDefinitionBuilder setResourceDescription(String resourceDescription) {
		this.beanDefinition.setResourceDescription(resourceDescription);
		return this;
	}

}

调用 代码 

 

		BeanDefinitionBuilder builder = BeanDefinitionBuilder.rootBeanDefinition(DeclareParentsAdvisor.class);
		builder.addConstructorArgValue(declareParentsElement.getAttribute(IMPLEMENT_INTERFACE));
		builder.addConstructorArgValue(declareParentsElement.getAttribute(TYPE_PATTERN));
		
		String defaultImpl = declareParentsElement.getAttribute(DEFAULT_IMPL);
		String delegateRef = declareParentsElement.getAttribute(DELEGATE_REF);
		
		if (StringUtils.hasText(defaultImpl) && !StringUtils.hasText(delegateRef)) {
			builder.addConstructorArgValue(defaultImpl);
		}
		else if (StringUtils.hasText(delegateRef) && !StringUtils.hasText(defaultImpl)) {
			builder.addConstructorArgReference(delegateRef);
		}
		else {
			parserContext.getReaderContext().error(
					"Exactly one of the " + DEFAULT_IMPL + " or " + DELEGATE_REF + " attributes must be specified",
					declareParentsElement, this.parseState.snapshot());
		}

		AbstractBeanDefinition definition = builder.getBeanDefinition();