Spring Setter Injection and Constructor Injection

Setter Injection

AppContext.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"
       xmlns:p="http://www.springframework.org/schema/p"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
          http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="messageRenderer"
        class="com.apress.prospring4.ch3.xml.StandardOutMessageRenderer"
        p:messageProvider-ref="messageProvider"/>

    <bean id="messageProvider"
        class="com.apress.prospring4.ch3.xml.HelloWorldMessageProvider"/>
</beans>

Source Code

package com.apress.prospring4.ch3;

public interface MessageRenderer {
    void render();
    void setMessageProvider(MessageProvider provider);
    MessageProvider getMessageProvider();
}

package com.apress.prospring4.ch3;

public interface MessageProvider {
    String getMessage();
}

package com.apress.prospring4.ch3.xml;

import com.apress.prospring4.ch3.MessageProvider;

public class HelloWorldMessageProvider implements MessageProvider {
    @Override
    public String getMessage() {
        return "Hello World!";
    }
}

package com.apress.prospring4.ch3.xml;

import com.apress.prospring4.ch3.MessageProvider;
import com.apress.prospring4.ch3.MessageRenderer;

public class StandardOutMessageRenderer implements MessageRenderer {
    private MessageProvider messageProvider;

    @Override
    public void render() {
        if (messageProvider == null) {
            throw new RuntimeException(
            "You must set the property messageProvider of class:"
            + StandardOutMessageRenderer.class.getName());
        }

        System.out.println(messageProvider.getMessage());
    }

    @Override
    public void setMessageProvider(MessageProvider provider) {
        this.messageProvider = provider;
    }

    @Override
    public MessageProvider getMessageProvider() {
        return this.messageProvider;
    }
}

package com.apress.prospring4.ch3;

import org.springframework.context.support.GenericXmlApplicationContext;

public class DeclareSpringComponents {
    public static void main(String[] args) {
        GenericXmlApplicationContext ctx = new GenericXmlApplicationContext();
        ctx.load("classpath:META-INF/spring/app-context-xml.xml");
        ctx.refresh();

        MessageRenderer messageRenderer = ctx.getBean("messageRenderer",
            MessageRenderer.class);

        messageRenderer.render();
    }
}

Constructor Injection

AppContext.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"
    xmlns:c="http://www.springframework.org/schema/c"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="messageProvider"
        class="com.apress.prospring4.ch3.xml.ConfigurableMessageProvider"
        c:message="This is a configurable message"/>

    <bean id="constructorConfusion"
        class="com.apress.prospring4.ch3.xml.ConstructorConfusion">
        <constructor-arg type="int">
            <value>90</value>
        </constructor-arg>
    </bean>
</beans>

Source code

package com.apress.prospring4.ch3;

public interface MessageProvider {
    String getMessage();
}

package com.apress.prospring4.ch3.xml;

import com.apress.prospring4.ch3.MessageProvider;

public class ConfigurableMessageProvider implements MessageProvider {
    private String message;

    public ConfigurableMessageProvider(String message) {
        this.message = message;
    }

    @Override
    public String getMessage() {
        return message;
    }
}

package com.apress.prospring4.ch3.xml;
import  com.apress.prospring4.ch3.MessageProvider;

import org.springframework.context.support.GenericXmlApplicationContext;

public class ConstructorConfusion {
    private String someValue;

    public ConstructorConfusion(String someValue) {
        System.out.println("ConstructorConfusion(String) called");
        this.someValue = someValue;
    }

    public ConstructorConfusion(int someValue) {
        System.out.println("ConstructorConfusion(int) called");
        this.someValue = "Number: " + Integer.toString(someValue);
    }

    public static void main(String[] args) {
        GenericXmlApplicationContext ctx = new GenericXmlApplicationContext();
        ctx.load("classpath:META-INF/spring/app-context-xml.xml");
        ctx.refresh();

        ConstructorConfusion cc = (ConstructorConfusion) ctx.getBean("constructorConfusion");
        System.out.println(cc); 

        MessageProvider mp = (MessageProvider) ctx.getBean("messageProvider");
        System.out.println(mp.getMessage());

    }

    public String toString() {
        return someValue;
    }
}