Spring 入门


#Spring#


本文通过 3 个示例让大家对 spring 有一个直观的感受。

我们可以到 maven 仓库 查看spring的最新版本。

项目基于 Gradle 构建。

示例1

项目结构

├── build.gradle
└── src
    └── main
        ├── java
        │   └── demo
        │       ├── Main.java
        │       └── SayHello.java
        └── resources
            └── beans.xml

build.gradle

group 'com.example'
version '1.0-SNAPSHOT'

apply plugin: 'java'

sourceCompatibility = 1.8

dependencies {
    implementation group: 'org.springframework', name: 'spring-context', version: '5.0.6.RELEASE'
}

SayHello.java

package demo;

public class SayHello {

    public String sayHello(String name) {
        return "Hello, " + name;
    }

}

beans.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-2.5.xsd">

    <bean id="sayHello" class="demo.SayHello">
    </bean>

</beans>

Main.java:

package demo;

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

public class Main {

    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
        SayHello sayHello = (SayHello) ctx.getBean("sayHello");
        System.out.println(sayHello.sayHello("world"));
    }

}

执行结果

运行 Main 类,会输出:

Hello, world

除此之外,也会输出一些 Spring 的信息,例如:

三月 04, 2019 8:00:51 上午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@4ee285c6: startup date [Mon Mar 04 08:00:51 CST 2019]; root of context hierarchy
三月 04, 2019 8:00:51 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans.xml]

示例2

项目结构

├── build.gradle
└── src
    └── main
        ├── java
        │   └── demo
        │       ├── Main.java
        │       └── bean
        │           ├── Address.java
        │           └── Person.java
        └── resources
            └── beans.xml

Address.java

package demo.bean;

public class Address {

    private String province;

    public String getProvince() {
        return province;
    }

    public void setProvince(String province) {
        this.province = province;
    }

    @Override
    public String toString() {
        return "Address{" +
                "province='" + province + '\'' +
                '}';
    }

}

Person.java

package demo.bean;

public class Person {

    private Address address;

    public Address getAddress() {
        return address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "Person{" +
                "address=" + address +
                '}';
    }

}

beans.xml

beans.xml 中配置bean,通过property向bean中注入数据:

<?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-2.5.xsd">

    <bean id="ltt" class="demo.bean.Person">
        <property name="address" ref="address" />
    </bean>
    <bean id="address" class="demo.bean.Address" scope="singleton">
        <property name="province" value="上海"/>
    </bean>

</beans>

Main.java

Main 类内容:

package demo;

import demo.bean.Person;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {

    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
        Person ltt = (Person) ctx.getBean("ltt");
        System.out.println(ltt);
    }

}

执行结果

Main 类运行后输出:

Person{address=Address{province='上海'}}

示例3

这里对示例2中代码稍作改动,通过引入@Autowired注解减少beans.xml中的配置。autowired 意思是自动装配

首先将 beans.xml 修改为:

<?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-2.5.xsd">

    <!-- 注意这个新引入的 Spring 类  -->
    <bean class="org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor"/>

    <bean id="ltt" class="demo.bean.Person">
        <!-- 这里不再注入其他bean -->
    </bean>
    <bean id="address" class="demo.bean.Address" scope="singleton">
        <property name="province" value="上海"/>
    </bean>

</beans>

将 Person 类改成:

package demo.bean;

import org.springframework.beans.factory.annotation.Autowired;

public class Person {

    @Autowired
    private Address address;  // 变量名,不叫 address 也行,这说明默认是基于类型进行注入

    @Override
    public String toString() {
        return "Person{" +
                "address=" + address +
                '}';
    }
}

Main 类内容:

package demo;

import demo.bean.Person;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class Main {

    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml");
        Person ltt = (Person) ctx.getBean("ltt");
        System.out.println(ltt);
    }

}

运行后,输出:

Person{address=Address{province='上海'}}

( 本文完 )