Spring实例化bean对象的方式

1、Instantiation with a Constructor（构造函数）
创建类DaoImpl1

package com.it.app.dao;
public class DaoImpl1 {

    private String name;
    private Integer age;
    public DaoImpl1(String name, Integer age){
        this.name = name;
        this.age = age;
    }
    public String getName() {
        return name;
    }

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

    public Integer getAge() {
        return age;
    }

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

    @Override
    public String toString() {
        return "DaoImpl1{" +
                "name='" + name + ''' +
                ", age=" + age +
                '}';
    }
}

spring-context.xml文件：daoImpl1

执行测试类：

package com.it.app;

import com.it.app.dao.DaoImpl1;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");

        DaoImpl1 daoImpl1 = (DaoImpl1) context.getBean("daoImpl1");

        System.out.println(daoImpl1.toString());


    }
}

2、Instantiation with a Static Factory Method（通过静态工厂 Factory Method）：

package com.it.app.dao;

public class DaoImpl2 {

    private static DaoImpl2 daoImpl2 = new DaoImpl2();

    private DaoImpl2(){

    }

    public static DaoImpl2 createDaoimpl2(){
        return daoImpl2;
    }
}

spring-context.xml文件：daoImpl2

执行测试代码：

package com.it.app;

import com.it.app.dao.DaoImpl1;
import com.it.app.dao.DaoImpl2;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");

        DaoImpl2 daoImpl2 = (DaoImpl2) context.getBean("daoImpl2");

        System.out.println(daoImpl2.toString());


    }
}

3、Instantiation by Using an Instance Factory Method（实例化工厂）
创建DaoImpl3：

package com.it.app.dao;

public class DaoImpl3 {

    private static DaoImpl3 daoImpl3 = new DaoImpl3();

    public DaoImpl3 createDaoImpl3(){
        return daoImpl3;
    }
}

spring-context.xml文件：

执行测试类：

package com.it.app;

import com.it.app.dao.DaoImpl1;
import com.it.app.dao.DaoImpl2;
import com.it.app.dao.DaoImpl3;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class App {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("spring-context.xml");

        DaoImpl3 daoImpl3 = (DaoImpl3) context.getBean("daoImpl3Factory");

        System.out.println(daoImpl3.toString());


    }
}