========
工厂方法
========

Spring工厂创建的对象称为Bean或者组件(Component)。

每个Bean在工厂配置文件中占一个Bean标签：

                        一个Bean
 ___________________________|__________________________
/                                                      \
<bean id="student" class="cn.tedu.hellospring.Student"/>
      \__________/ \_________________________________/
           |                        |
        Bean的ID                Bean的类型

ApplicationContext接口方法：

- Object getBean(String s)
  根据ID获取Bean，返回Object类型的对象，需要类型转换

- T getBean(String s, Class<T> aClass)
  根据ID获取Bean，返回指定类型的对象，无需类型转换

- T getBean(Class<T> aClass)
  根据指定类型获取Bean，该类型的Bean在工厂配置文件中只能有一个

- String[] getBeanDefinitionNames()
  获取工厂配置文件中所有Bean的ID

- String[] getBeanNamesForType(Class<?> aClass)
  获取工厂配置文件中所有指定类型的Bean的ID

- boolean containsBeanDefinition(String s)
  判断工厂配置文件中是否包含指定ID的Bean

- boolean containsBean(String s)
  判断工厂配置文件中是否包含指定ID或别名的Bean

/src/test/java/cn/tedu/hellospring/StudentTest.java：

class StudentTest {
    @org.junit.jupiter.api.Test
    void test1() {
        ApplicationContext applicationContext =
            new ClassPathXmlApplicationContext("/applicationContext.xml");
        Student student = (Student) applicationContext.getBean("student");
        System.out.println(student);
    }

    @org.junit.jupiter.api.Test
    void test2() {
        ApplicationContext applicationContext =
            new ClassPathXmlApplicationContext("/applicationContext.xml");
        Student student = applicationContext.getBean("student", Student.class);
        System.out.println(student);
    }

    @org.junit.jupiter.api.Test
    void test3() {
        ApplicationContext applicationContext =
            new ClassPathXmlApplicationContext("/applicationContext.xml");
        Student student = applicationContext.getBean(Student.class);
        System.out.println(student);
    }

    @org.junit.jupiter.api.Test
    void test4() {
        ApplicationContext applicationContext =
            new ClassPathXmlApplicationContext("/applicationContext.xml");
        String[] beanNames = applicationContext.getBeanDefinitionNames();
        for (String beanName : beanNames)
            System.out.println(beanName);
    }

    @org.junit.jupiter.api.Test
    void test5() {
        ApplicationContext applicationContext =
            new ClassPathXmlApplicationContext("/applicationContext.xml");
        String[] beanNames =
            applicationContext.getBeanNamesForType(Student.class);
        for (String beanName : beanNames)
            System.out.println(beanName);
    }

    @org.junit.jupiter.api.Test
    void test6() {
        ApplicationContext applicationContext =
            new ClassPathXmlApplicationContext("/applicationContext.xml");
        System.out.println(
            applicationContext.containsBeanDefinition("student"));
    }


    @org.junit.jupiter.api.Test
    void test7() {
        ApplicationContext applicationContext =
            new ClassPathXmlApplicationContext("/applicationContext.xml");
        System.out.println(
            applicationContext.containsBean("student"));
    }
}

例程：HelloSpring