Spring IOC bean registered instantiated

Sign up and instantiated bean

Usually created in xml application beginning as bean configuration metadata attributes in the resource directory, by defining managed bean registration and instantiation.

set method

<!-- 一个bean标签就表示一个对象, id：这个对象的唯一标识, name：类似别名, class：注册对象的完全限定名 -->
<!-- 使用setter注入，绑定方法名setXXX，name属性值必须与XXX一致，并且setter方法必须为public -->
<!-- 通过setter注入，实际是通过反射调用类的无参构造，所以在显示为类定义构造方法的时候不要忘记添加一个无参构造 -->
<bean id="person1" name="person" class="com.nanborone.bean.Person">
    <!-- 使用property标签给对象的属性赋值, name：表示属性的名称, value：表示属性的值 -->
    <property name="id" value="1"/>
    <property name="name" value="nanborone"/>
    <property name="male" value="true"/>
</bean>

Construction method

<!-- 使用constructor注入，绑定构造方法形参名XXX，name属性值必须与XXX一致 -->
<!-- constructor-arg个数必须与已有的构造器参数个数相同 -->
<bean id="person2" class="com.nanborone.bean.Person">
	<!-- 使用constructor-arg标签在对象构造的时候给属性赋值, name：表示属性的名称, value：表示属性的值 -->
	<!-- 在使用构造器赋值的时候可以省略name属性，但是此时就要求必须严格按照构造器参数的顺序来填写了 -->
	<!-- 如果name属性省略且有相同参数个数的构造器，后定义的会覆盖先定义的除非指定type来匹配确定的构造器 -->
    <constructor-arg name="id" value="2"/>
    <constructor-arg name="name" value="nanborone"/>
    <constructor-arg name="male" value="true"/>
</bean>
<bean id="person3" class="com.nanborone.bean.Person">
	<!-- 如果想不按照顺序来添加参数值，那么可以搭配index属性来使用 -->
    <constructor-arg value="3"/>
    <constructor-arg value="true" index="2"/>
    <constructor-arg value="nanborone" index="1"/>
</bean>
<bean id="person4" class="com.nanborone.bean.Person">
	<!-- 可以使用type属性来指定类型，但是无法自动拆装箱，可以用type="int" -->
    <constructor-arg value="4" type="int"/>
    <constructor-arg value="nanborone" type="java.lang.String"/>
    <constructor-arg value="true" index="2"/>
</bean>

Spring String can also be converted into the default Java built-in types. For example int, long, String, booleanetc., through StringToXXXConverter.

Normally we only use the most simple attributes injection method, the simplest constructor injection occasionally use, basically do not mess plus the rest of the property.

Factory Pattern

In the previous case, bean create all objects are obtained by reflection corresponding bean instance, in fact, in the spring further comprises another bean created way of example, is created by a factory object model.

<!-- 静态工厂：不需要创建工厂类实例，通过类方法（静态方法）来获得bean -->
<!-- class：指定静态工厂类, factory-method：指定哪个方法是工厂方法 -->
<bean id="person1" class="com.nanborone.bean.factory.PersonStaticFactory" factory-method="getInstance">
    <!--constructor-arg：可以为方法指定参数-->
    <constructor-arg value="nanborone" />
</bean>

<!-- 实例工厂：需要先创建工厂类实例，再通过实例调用实例方法来获得bean-->
<bean id="personInstanceFactory" class="com.nanborone.bean.factory.PersonInstanceFactory" />
<!-- factory-bean：指定使用哪个工厂实例, factory-method：指定使用哪个工厂实例的方法 -->
<bean id="person2" class="com.nanborone.bean.Person" factory-bean="personInstanceFactory" factory-method="getInstance">
    <constructor-arg value="nanborone" />
</bean>

Creates a corresponding static factory class and instance of the factory class:

public class PersonStaticFactory {
    public static Person getInstance(String name) {
        return new Person(1, name, true);
    }
}
public class PersonInstanceFactory {
    public Person getInstance(String name) {
        return new Person(1, name, true);
    }
}

FactoryBean

FactoryBean is an interface, the interface implementation class specified in Spring, Spring will be used as a factory, but does not create a start when Ioc container instance, only when in use will create an object, whether it is not a single case .

<bean id="myFactoryBean" class="com.nanborone.bean.factorybean.MyFactoryBean" />

Creating MyFactoryBean categories:

public class MyFactoryBean implements FactoryBean<Person> {

	// 工厂方法，返回需要创建的对象
    @Override
    public Person getObject() throws Exception {
        System.out.println("通过MyFactoryBean创建");
        return new Person(1, "nanborone, true);
    }

    // 返回创建对象的类型,spring会自动调用该方法返回对象的类型
    @Override
    public Class<?> getObjectType() {
        return Person.class;
    }

    // 创建的对象是否是单例对象
    @Override
    public boolean isSingleton() {
        return false;
    }
}

When tested by the need to get the person instance myFactoryBean

public class IocTest {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
        Person person = context.getBean("myfactorybean", Person.class);
        System.out.println(person);
    }
}