Spring注解开发

JavaConfig

从Spring 3起，JavaConfig功能已经包含在Spring核心模块，它允许开发者将bean定义和在Spring配置XML文件到Java类中。但是，仍然允许使用经典的XML方式来定义bean和配置，JavaConfig是另一种替代解决方案。所以，在Spring3以后的版本中，支持xml方式和javaConfig两种Spring配置方式。

建议：Spring项目用全注解开发，为后期学Spring Boot和Spring Cloud打好基础。

通过XML配置

Person.java

package com.spring;

public class Person {
    private String name;
    private String age;

    public Person(String name, String age) {
        this.name = name;
        this.age = age;
    }

    public Person() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

bean.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
	<!--
		配置bean
		class：bean的全类名，通过反射的方式在IOC容器中创建Bean，所以要求Bean中必须有无参数的构造器
		id:标识容器中的bean。id唯一
	-->
    <bean id="person" class="com.Spring.Person">
        <property name="name" value="HuiProgramer"></property>
        <property name="age" value="21"></property>
    </bean>
</beans>

Maintest.java

package com.Spring;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainTest {
    public static void main(String[] args){
        //1.创建Spring 的IOC容器对象
        //ApplicationContext 代表IOC容器
        //ClassPathXmlApplicationContext：是ApplicationContext 接口的实现类
        ApplicationContext act = new ClassPathXmlApplicationContext("bean.xml");
        //2.从IOC容器中获取Bean实例
        Person person = (Person)act.getBean("person");
        //3.调用toString()方法并打印
        System.out.println(person.toString());
    }
}
}

结果：
Person{name='HuiProgramer', age='21'}

以上为Xml配置的方式，Spring3.0后启用注解开发模式。

使用注解模式

Person.java

package com.spring;

public class Person {
    private String name;
    private String age;

    public Person(String name, String age) {
        this.name = name;
        this.age = age;
    }

    public Person() {
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age='" + age + '\'' +
                '}';
    }
}

AppConfig.java

package com.spring;

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

//相当于beans
@Configuration
public class AppConfig {
    public AppConfig(){
    }
	//相当于bean，默认方法名为Bean的id
    @Bean
    public Person person(){
        return new Person("HuiPerson","21");
    }
}

MainTest.Java

public class Maintest{
	public static void main(String[] args){
			//通过注解获取ApplicationContext
	        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
			//通过类获取Person的bean实例
	        Person person = context.getBean(Person.class);
			//打印person
	        System.out.println(person);
			//通过类型获取所有Bean的person bean实例
	        String[] names = context.getBeanNamesForType(Person.class);
			//打印
	        for(String name:names)
	            System.out.println(name);
	    }
}

结果：
Person{name='HuiProgramer', age='21'}
person

此为Spring3.0后的注解开发模式！