Understand bean on spring framework 1- by xml file

2020-08-24

Dependancy about spring-framework ( not spring-boot)

It’s just spring framwork (not springboot, we only need to include some necessary packages)

1
2
3
4
5
6
7
8
9
10
11
12
<!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-core</artifactId>
    <version>5.2.8.RELEASE</version>
</dependency>

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.2.8.RELEASE</version>
</dependency>

Define xml file for beans

create xml at ‘src/main/resources/beans.xml’

has supported several different tags

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26

<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 id="iwang" class="com.mycompany.app.User">
        <property name="name" value="iwang"/>
         <property name="car" ref = "car1" />
    </bean>

    <bean id="car1" class="com.mycompany.app.Car">
        <property name="name" value="bmw"/>

        <property name="session">
            <map>
                <entry key="uid" value="9527"/>
                <entry key="username" value="Jack"/>
                <entry key="password" value="1234"/>
            </map>
        </property>

    </bean>

</beans>

in above xml, User class refer the ‘car’ as a private variable.

Define User and Car Class

After we define xml file, we need to implement Bean classes, User and Car

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
package com.mycompany.app;

import javax.swing.plaf.synth.SynthTextAreaUI;

public class User {
    private String name;
    private Car car;

    public User(){
    }

    public String getName(){return this.name;}
    public void setName(String n){ this.name = n;}
    public void setCar(Car c){
        System.out.println("got setcar:" + c.getName());
        this.car = c;
    }
    public Car getCar(){return this.car;}
    public void show(){
        this.car.drive();
    }
}
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
package com.mycompany.app;

import java.util.HashMap;

public class Car {
    private String name;

    private HashMap<String, String> session;

    public Car(){};

    public void setName(String name){
        System.out.println("set named:" + name);
        this.name = name;
    }
    public String getName(){
        return this.name;
    }

    public void setSession( HashMap<String, String> s ){
        this.session = s;
    }

    public HashMap<String, String> getSession() {
        return this.session;
    }
    
    public void drive(){
        System.out.println("starting drive now!" + this.session.get("username"));

    }
}

Load and test beans.xml

1
2
3
4
5
6
7
8
9
10
11
12
13
14
package com.mycompany.app;

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


public class App 
{
    public static void main( String[] args ) {
        ApplicationContext  applicationContext  =  new ClassPathXmlApplicationContext("beans.xml");
        User u = (User) applicationContext.getBean("iwang");
        u.show();
    }
}

By default, bean factory create singleton instance of class defined in bean.