In the previous two examples you have seen how to access member of a collection and access a map element using the square-braces []
operator in Spring EL. In this example you will see how to use the []
operator to read a value from a properties file or java.util.Properties
.
Let’s say we have a database properties file called database.properties
with the following entries in it:
jdbc.driverClassName=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost/kodejava
jdbc.username=root
jdbc.password=secret
First, let’s create the spring configuration file. In this configuration we will use the <util:properties>
to load the properties file into Spring. And then we will use Spring EL to access the value of these properties and assign it to some bean’s properties.
<?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:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">
<util:properties id="database" location="classpath:database.properties" />
<bean id="dataSource" class="org.kodejava.spring.core.el.MyDataSource">
<property name="driverClassName" value="#{database['jdbc.driverClassName']}" />
<property name="url" value="#{database['jdbc.url']}" />
<property name="username" value="#{database['jdbc.username']}" />
<property name="password" value="#{database['jdbc.password']}" />
</bean>
</beans>
To read a value from properties file what you do is the same as how we access an element of a map object. We pass the name of the properties as the key in the Spring EL.
<property name="driverClassName" value="#{database['jdbc.driverClassName']}"/>
The MyDataSource
class is an imaginary data source object. It has some properties such as the driverClassName
, url
, username
and password
. It’s a common parameter you use to connect to a database using a JDBC driver. For simplicity the getters and setters we removed from the class.
package org.kodejava.spring.core.el;
public class MyDataSource {
private String driverClassName;
private String url;
private String username;
private String password;
// Getters & Setters
}
As always, to run the Spring configuration above we will need to create a main class that load and execute the application context. This class will obtain the dataSource bean from the application context and print out its properties whose values are read from a properties file called database.properties.
package org.kodejava.spring.core.el;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class SpELPropertiesExample {
public static void main(String[] args) {
try (ClassPathXmlApplicationContext context =
new ClassPathXmlApplicationContext("spel-properties.xml")) {
MyDataSource dataSource = (MyDataSource) context.getBean("dataSource");
System.out.println("driverClassName = " + dataSource.getDriverClassName());
System.out.println("url = " + dataSource.getUrl());
System.out.println("username = " + dataSource.getUsername());
System.out.println("password = " + dataSource.getPassword());
}
}
}
Here are the result you get when running the code snippet:
driverClassName = com.mysql.cj.jdbc.Driver
url = jdbc:mysql://localhost/kodejava
username = root
password = secret
Maven Dependencies
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>5.3.23</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-beans</artifactId>
<version>5.3.23</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context-support</artifactId>
<version>5.3.23</version>
</dependency>
</dependencies>
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Hi, i have a problem with
util:properties
, error (The prefixutil
for elementutil:properties
is not bound). Thanks!Hi Adrian,
Have you correctly define the namespace and the schema location for the util element in your Spring configuration file?
For setting a propertie value is the same way?
Please see the xml file is there any util in your xml header.