Ebooks

Spring p-namespace tutorial

Spring property namespace tutorial shows how to use p-namespace in property-based injection in a Spring application.

Spring is a popular Java application framework for creating enterprise applications.

Spring p-namespace

Spring p-namespace is an XML shortcut and replacement of the <property/> subelement of the <bean/> tag. To enable the p-namespace feature, we need to add the xmlns:p="http://www.springframework.org/schema/p" into the XML file. Note that this namespace does not have a separate XSD file; therefore, IDEs such as IntelliJ do not recognize it.

Spring p-namespace example

The application contains two HelloMessage beans. One is injected with the older <property/>, the other one with the newer p-namespace attribute.

src
├───main
│   ├───java
│   │   └───com
│   │       └───zetcode
│   │           │   Application.java
│   │           └───bean
│   │                   HelloMessage.java
│   └───resources
│           logback.xml
│           my-beans.xml
└───test
    └───java

This is the project structure.

pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<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.zetcode</groupId>
    <artifactId>cnamespace</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>
        <spring-version>5.1.3.RELEASE</spring-version>

    </properties>

    <dependencies>

        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.3</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>${spring-version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring-version}</version>
        </dependency>
        
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                <version>1.6.0</version>
                <configuration>
                    <mainClass>com.zetcode.Application</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

In the pom.xml file, we have basic Spring dependencies spring-core and spring-context and logging logback-classic dependency.

The exec-maven-plugin is used for executing Spring application from the Maven on the command line.

resources/logback.xml
<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <logger name="org.springframework" level="ERROR"/>
    <logger name="com.zetcode" level="INFO"/>

    <appender name="consoleAppender" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <Pattern>%d{HH:mm:ss.SSS} %blue(%-5level) %magenta(%logger{36}) - %msg %n
            </Pattern>
        </encoder>
    </appender>

    <root>
        <level value="INFO" />
        <appender-ref ref="consoleAppender" />
    </root>
</configuration>

The logback.xml is a configuration file for the Logback logging library.

resources/my-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"
        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 name="msg1" class="com.zetcode.bean.HelloMessage">
        <property name="message" value="How are you?"/>
    </bean>

    <bean name="msg2" class="com.zetcode.bean.HelloMessage" p:message="Hello there"/>

</beans>

The my-beans.xml file declares two beans: msg1 and msg2. The msg1 uses <property/> tag to inject its values, while msg2 uses p:message attribute.

com/zetcode/bean/HelloMessage.java
package com.zetcode.bean;

public class HelloMessage {

    private String message;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {

        this.message = message;
    }
}

This is the HelloMessage class that is managed by Spring container. It must contain a setter method because we use property-based injection in our application.

com/zetcode/Application.java
package com.zetcode;

import com.zetcode.bean.HelloMessage;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.support.GenericXmlApplicationContext;

public class Application {

    private static final Logger logger = LoggerFactory.getLogger(Application.class);

    public static void main(String[] args) {

        var ctx = new GenericXmlApplicationContext("my-beans.xml");

        var msg1 = (HelloMessage) ctx.getBean("msg1");
        logger.info("{}", msg1.getMessage());

        var msg2 = (HelloMessage) ctx.getBean("msg2");
        logger.info("{}", msg2.getMessage());

        ctx.close();
    }
}

This is the main application class. It retrieves the two HelloMessage beans and prints them to the console.

$ mvn -q exec:java
16:52:11.257 [main] INFO  com.zetcode.Application - How are you? 
16:52:11.273 [main] INFO  com.zetcode.Application - Hello there 

We run the application.

In this tutorial, we have shown how to use property-based injection with p-namespace.

You might also be interested in these related tutorials: Spring @Qualifier annotation tutorial, Spring Singleton scope bean, Spring c-namespace tutorial, Spring BeanDefinitionBuilder tutorial, Spring HikariCP tutorial, and Java tutorial.