spring创建bean

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

一、通过构造函数创建对象。

2.1 利用无参构造函数+setter方法注入值

最基本的对象创建方式，只需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，如果写了任何一个构造函数，默认的无参构造函数就不会自动创建哦!!）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创建一个对象，然后利用setter方法赋值。所以如果无参构造函数不存在，Spring上下文创建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>

二、通过静态方法创建对象。

 

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作用)      * @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>

 

三、通过工厂方法创建对象。

 

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

    <!-- 实例工程方法需要先创建工厂实例，然后在创建所需对象的时候，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>