spring factory-method

配置工厂Bean

通常由应用程序直接使用new创建新的对象,为了将对象的创建和使用相分离,采用工厂模式,即应用程序将对象的创建及初始化职责交给工厂对象.

一般情况下,应用程序有自己的工厂对象来创建bean.如果将应用程序自己的工厂对象交给Spring管理,那么Spring管理的就不是普通的bean,而是工厂Bean.

调用getBean()方法,Spring返回的不是直接创建的Bean的实例,而是由工厂Bean创建的Bean实例.

一般在Spring中配置工厂Bean,有3中不同类型的工厂Bean的配置.

1.静态工厂

创建具体Bean实例的是静态方法

import java.util.Random;

public class StaticFactoryBean {

public static Integer createRandom() {

return new Integer(new Random().nextInt());
}
}

将其纳入Spring容器来管理,需要通过factory-method指定静态方法名称

<bean id="random"
class="example.chapter3.StaticFactoryBean"
factory-method="createRandom" //createRandom方法必须是static的,才能找到
scope="prototype"
/>

测试:

public static void main(String[] args) {

XmlBeanFactory factory = new XmlBeanFactory(new ClassPathResource("config.xml"));
System.out.println(factory.getBean("random").toString());

//StaticFactoryBean sfb = (StaticFactoryBean)factory.getBean("random");
//System.out.println(sfb.createRandom().toString());

//调用getBean()时,返回随机数.如果没有指定factory-method,会返回StaticFactoryBean的实例,即返回工厂Bean的实例
}

2.实例工厂

创建具体Bean实例的是实例,不是静态方法

import java.text.SimpleDateFormat;
import java.util.Date;

public class InstanceFactoryBean {

private String format = "yy-MM-dd HH:mm:ss";

public void setFormat(String format) {
this.format = format;
}

public String createTime() {
return new SimpleDateFormat(format).format(new Date());
}
}

配置文件需要配置两个bean:第一个Bean和普通的Bean没有区别,第二个bean定义如何通过工厂Bean获取Bean,需要指定 工厂Bean的名称和方法名称

<bean id="instanceFactoryBean" class="example.chapter3.InstanceFactoryBean">
<property name="format" value="yyyy-MM-dd HH:mm:ss" />
</bean>

<bean id="currentTime"
factory-bean="instanceFactoryBean"
factory-method="createTime"
/>

测试:

public static void main(String[] args) {

XmlBeanFactory factory = new XmlBeanFactory(new ClassPathResource("config.xml"));
System.out.println(factory.getBean("currentTime"));

}

3.实现FactoryBean接口

public class PiFactoryBean implements FactoryBean {

public Object getObject() throws Exception {
return new Double(3.14159265358979);
}

public Class getObjectType() {
return Double.class;
}

public boolean isSingleton() {
return true;
}

}

实现了FactoryBean接口的Bean,不再被视为普通的Bean.Spring会自动检测.

<bean id="pi" class="example.chapter3.PiFactoryBean" />

测试

public static void main(String[] args) throws Exception {

XmlBeanFactory factory = new XmlBeanFactory(new ClassPathResource("config.xml"));
System.out.println(factory.getBean("pi"));//返回PiFactoryBean 的工厂方法getObject返回的Double对象实例
//PiFactoryBean p = (PiFactoryBean)factory.getBean("&pi"); //加"&"返回工厂Bean的实例.
//System.out.println(p.getObject());
}

 

 

 

动态传参数

class ExampleBean {
  private String string;
  public ExampleBean(String string) {
    this.string = string;
  }
}

class ExampleBeanFactory {
  public static ExampleBean createExampleBean(String string) {
    return new ExampleBean(string);
  }
}

<bean id="exampleBean" class="...ExampleBeanFactory"  scope="prototype"
        factory-method="createExampleBean">
    <constructor-arg value="default value"/>
</bean>


public class Main {
  public static void main(String[] args) {
    ApplicationContext context = new ClassPathXmlApplicationContext(
                    "context.xml");
    ExampleBean exampleBean =
            ExampleBean)context.getBean("exampleBean",
              new Object[]{"bla bla"});
    exampleBean.write();
  }
}