Spring建立对象的方式3种方式

此文为基础回顾，估计是最后一次总结。

项目利用maven进行架构，其基本项目结构为：

其中pom.xml中的内容为：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.mc.base.learn</groupId>
    <artifactId>spring</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>spring</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>

        <!-- Spring核心依赖 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>4.2.6.RELEASE</version>
        </dependency>
        
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>4.2.6.RELEASE</version>
        </dependency>

        <!-- 提供了Spring上下文对象 -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>4.2.6.RELEASE</version>
        </dependency>
        
    </dependencies>
</project>

项目基本结构完成

1、经过构造函数建立对象。

2.1 利用无参构造函数+setter方法注入值

最基本的对象建立方式，只须要有一个无参构造函数（类中没有写任何的构造函数，默认就是有一个构造函数，若是写了任何一个构造函数，默认的无参构造函数就不会自动建立哦!!）和字段的setter方法。

Person类：

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>

其本质为：

SpringContext利用无参的构造函数建立一个对象，而后利用setter方法赋值。因此若是无参构造函数不存在，Spring上下文建立对象的时候便会报错。

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) 　　。。。。。

2.2 利用有参构造函数直接注入

Person类：

package com.mc.base.learn.spring.bean; public class Person { private String name; private Integer id; public Person(String name, Integer id) { super(); this.name = name; this.id = 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">
        <constructor-arg name="id" value="123"></constructor-arg>
        <constructor-arg name="name" value="LiuChunfu"></constructor-arg>
    </bean>
    
</beans>

2、经过静态方法建立对象。

 

package com.mc.base.learn.spring.factory; import com.mc.base.learn.spring.bean.Person; public class PersonStaticFactory { public static Person createPerson(){ return new Person(); } /** * 工厂方法带有参数如何处理？ * @Title: createPerson * @Description: TODO(这里用一句话描述这个方法的做用) * @param  @param id * @param  @param name * @param  @return * @return Person 返回类型 * @throws
     */
    public static Person createPerson(Integer id,String name){ return new Person(name,id); } }

<!--静态的工厂方法核心是class+factory-method -->
    <bean id="person" class="com.mc.base.learn.spring.factory.PersonStaticFactory" factory-method="createPerson"></bean>

 

3、经过工厂方法建立对象。

 

package com.mc.base.learn.spring.factory; import com.mc.base.learn.spring.bean.Person; public class PersonFactory { public Person createInstance() { return new Person(); } }

<!-- 实例工程方法须要先建立工厂实例，而后在建立所需对象的时候，将其赋值为factory-bean -->
    <bean id="personFactory" class="com.mc.base.learn.spring.factory.PersonFactory"></bean>
    <bean id="person2" factory-bean="personFactory" factory-method="createInstance"></bean>

 

setter方法设置属性