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