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public static Object instantiate(ClassLoader cls, String beanName) throws IOException, ClassNotFoundException {
    return Beans.instantiate(cls, beanName, null, null);
}

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@Autowired
private User user;

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// 根据 Bean 的名字去查找
public Object lookup(Name name) throws NamingException;

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@EJB  // 2005 年
private DataSource datasource;

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public <T> T getBean(Class<T> requiredType, @Nullable Object... args) throws BeansException {
    Object resolved = this.resolveBean(ResolvableType.forRawClass(requiredType), args, false);
    if (resolved == null) {
        throw new NoSuchBeanDefinitionException(requiredType);
    } else {
        return resolved;
    }
}
@Nullable
private <T> T resolveBean(ResolvableType requiredType, @Nullable Object[] args, boolean nonUniqueAsNull) {
    NamedBeanHolder<T> namedBean = this.resolveNamedBean(requiredType, args, nonUniqueAsNull);
    if (namedBean != null) {
        return namedBean.getBeanInstance();
    } else {
        BeanFactory parent = this.getParentBeanFactory();
        if (parent instanceof DefaultListableBeanFactory) {
            return ((DefaultListableBeanFactory)parent).resolveBean(requiredType, args, nonUniqueAsNull);
        } else if (parent != null) {
            ObjectProvider<T> parentProvider = parent.getBeanProvider(requiredType);
            if (args != null) {
                return parentProvider.getObject(args);
            } else {
                return nonUniqueAsNull ? parentProvider.getIfUnique() : parentProvider.getIfAvailable();
            }
        } else {
            return null;
        }
    }
}

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public class UserSpringDemo {
    public static void main(String[] args) throws NamingException {


        /***
         * 没有 DataSource 定义
         */
        DefaultListableBeanFactory parentBeanFactory = new DefaultListableBeanFactory();
        DefaultListableBeanFactory beanFactory1 = new DefaultListableBeanFactory();
        beanFactory1.setParentBeanFactory(parentBeanFactory);

        /***
         * Spring
         */
        // xml 存一下
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext();

        // 写法 1
        BeanFactory beanFactory = new DefaultListableBeanFactory();
        User user1 = (User) beanFactory.getBean("user");
        // 写法 2
        User user = (User) applicationContext.getBean("user");
        applicationContext.getBean("user", User.class);

        /***
         * 传递相应的参数
         */
        beanFactory.getBean("user", 1L, "darian");

        /****
         * EJB
         */
        Context context = new InitialContext();
        /***
         * JNDI = Java Naming And Directory Interface
         * Tomcat 容器
         */
        Context context1 = (Context) context.lookup("java/com/");
        DataSource dataSource = (DataSource) context1.lookup("java/com/datasource");
    }
}

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// 256 是一个经验值。
private final Map<String, BeanDefinition> beanDefinitionMap = new ConcurrentHashMap(256);

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public class UserBeanSpringDemo {
    // <Bean id="user" class="com......">
    //      <property id="id" value>
    //      <pro....
    public static void main(String[] args) {
        DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
        // 理解 Bean 定义 = BeanDefinition
        // XML = BeanDefinition
        // Annotation 也是 BeanDefinition   AnnotationBeanDefinition 是 2.5 以后的。
        BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(User.class);
        // User Bean 定义
        AbstractBeanDefinition userBeanDefinition = builder.getBeanDefinition();
        MutablePropertyValues propertyValues = new MutablePropertyValues();
        // <property name="id" value="1L">
        propertyValues.add("id", 1L);
        // <property name="name" value="Darian1996 ">
        propertyValues.add("name", "Darian1996");
        userBeanDefinition.setPropertyValues(propertyValues);
        // 注册
        beanFactory.registerBeanDefinition("user", userBeanDefinition);
        User user = beanFactory.getBean(User.class);
        System.out.println(user);

    }
}

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ClassLoader classLoader = null;
Class userClass = classLoader.loadClass("com.darian.studysourcecode.java.beans.User");
Constructor constructor = userClass.getConstructor();
User user2 = (User) constructor.newInstance();