Spring context:property-placeholder tutorial
last modified October 18, 2023
Spring context:property-placeholder tutorial shows how to use context:property-placeholder tag to externalize properties in a Spring application.
Spring is a popular Java application framework for creating enterprise applications.
Spring context:property-placeholder
The context:property-placeholder tag is used to externalize properties in a separate
file. It automatically configures PropertyPlaceholderConfigurer, which replaces
the ${} placeholders, which are resolved against a specified properties file
(as a Spring resource location).
Spring context:property-placeholder example
The application uses context:property-placeholder to configure
properties of a datasource.
pom.xml
src
├───main
│ ├───java
│ │ └───com
│ │ └───zetcode
│ │ Application.java
│ └───resources
│ database.properties
│ logback.xml
│ my-beans.xml
└───test
└───java
This is the project structure.
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.zetcode</groupId>
<artifactId>propertyplaceholder</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<maven.compiler.source>17</maven.compiler.source>
<maven.compiler.target>17</maven.compiler.target>
<spring-version>5.3.23</spring-version>
</properties>
<dependencies>
<dependency>
<groupId>ch.qos.logback</groupId>
<artifactId>logback-classic</artifactId>
<version>1.4.0</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring-version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>${spring-version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-jdbc</artifactId>
<version>${spring-version}</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>3.1.0</version>
<configuration>
<mainClass>com.zetcode.Application</mainClass>
</configuration>
</plugin>
</plugins>
</build>
</project>
In the pom.xml file, we have basic Spring dependencies spring-core,
spring-context, spring-jdbc and logging logback-classic dependency.
The exec-maven-plugin is used for executing Spring application from the
Maven on the command line.
<?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.
db.url=jdbc:h2:mem:testdb db.username=testuser db.password=s$cret
These values are externalized in a database.properties file. This approach
is more flexible than placing the values right into the XML file.
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<context:property-placeholder location="classpath:database.properties"/>
<bean id="dataSource" class="org.springframework.jdbc.datasource.SimpleDriverDataSource">
<property name="url" value="${db.url}"></property>
<property name="username" value="${db.username}"></property>
<property name="password" value="${db.password}"></property>
</bean>
</beans>
The context:property-placeholder specifies the location of the properties
file; in our case, it is database.properties file in any classpath directory.
<bean id="dataSource" class="org.springframework.jdbc.datasource.SimpleDriverDataSource">
<property name="url" value="${db.url}"></property>
<property name="username" value="${db.username}"></property>
<property name="password" value="${db.password}"></property>
</bean>
A dataSource bean is defined. It takes its values from the properties file via
the ${} syntax.
package com.zetcode;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.support.GenericXmlApplicationContext;
import org.springframework.jdbc.datasource.SimpleDriverDataSource;
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 dataSource = (SimpleDriverDataSource) ctx.getBean("dataSource");
logger.info("Url: {}", dataSource.getUrl());
logger.info("User name: {}", dataSource.getUsername());
logger.info("Password: {}", dataSource.getPassword());
ctx.close();
}
}
This is the main application class. It retrieves the dataSource bean
and prints its properties.
$ mvn -q exec:java 11:27:43.790 INFO com.zetcode.Application - Url: jdbc:h2:mem:testdb 11:27:43.790 INFO com.zetcode.Application - User name: testuser 11:27:43.790 INFO com.zetcode.Application - Password: s$cret
We run the application.
In this article we have shown how to use context:property-placeholder to
externalize properties.
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