最基本的物件建立方式，只需要有一個無參建構函式（類中沒有寫任何的建構函式，預設就是有一個建構函式，如果寫了任何一個建構函式，預設的無參建構函式就不會自動建立哦!!）和欄位的setter方法。

Person類：

package com.mc.base.learn.spring.bean;

public class Person {

    private String name;
    private Integer id;

    public String getName() {
        return name;
    }

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

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    @Override
    public String toString() {
        return "Person [name=" + name + ", id=" + id + "]";
    }

}

XML配置：

<?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">

    <bean class="com.mc.base.learn.spring.bean.Person" id="person"
 
>
        <property name="name" value="LiuChunfu"></property>
        <property name="id" value="125"></property>
    </bean>

</beans>

其本質為：

SpringContext利用無參的建構函式建立一個物件，然後利用setter方法賦值。所以如果無參建構函式不存在，Spring上下文建立物件的時候便會報錯。

Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'person' defined in class path resource [applicationContext.xml]: Instantiation of bean failed; 
nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.mc.base.learn.spring.bean.Person]: No default constructor found; 
nested exception is java.lang.NoSuchMethodException: com.mc.base.learn.spring.bean.Person.<init>()
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1105)
　　。。。。。