How do I filter collection members based on some criteria using Spring EL?

By I Wayan Saryada in Spring Core 0 Comment

In previous examples you have seen that we use the square-braces [] operator to select items from collection. In this post you will learn how to filter members of a collection with a certain criteria using the Spring EL. To do this Spring EL give you another special operator, the filter operator which can be typed like .?[], you can define the filter criteria inside the braces.

Beside the filter operator .?[] there are also operator that can select the first and the last matching items from collection. You can use the .^[] for selecting the first match and the .$[] operator to select the last match items from collection respectively.

As an example we will demonstrate here that we want to find a collection of books that have pages more than 250 and assign it to Library bean’s books properties. So let’s begin by defining a class called Book and Library which will have the following properties:

package org.kodejava.spring.core.el;

public class Book {
    private Long id;
    private String title;
    private String author;
    private String type;
    private int pages;

    // Getters & Setters

    @Override
    public String toString() {
        return "Book{" +
                "title='" + title + '\'' +
                ", author='" + author + '\'' +
                ", pages=" + pages +
                '}';
    }
}

package org.kodejava.spring.core.el;

import java.util.List;

public class Library {
    private List<Book> books;

    public List<Book> getBooks() {
        return books;
    }

    public void setBooks(List<Book> books) {
        this.books = books;
    }
}

After creating the Book and the Library class let’s now create the Spring configuration file for our demo. We will create a file and call it as spel-filter-collection.xml with the following lines of configuration in it.

<?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" 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 http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">

    <util:list id="books">
        <bean class="org.kodejava.spring.core.el.Book" p:title="Essential C# 4.0" p:author="Michaelis" p:pages="450" />
        <bean class="org.kodejava.spring.core.el.Book" p:title="User Stories Applied" p:author="Mike Cohen"
              p:pages="268" />
        <bean class="org.kodejava.spring.core.el.Book" p:title="Learning Android" p:author="Marco Gargenta"
              p:pages="245" />
        <bean class="org.kodejava.spring.core.el.Book" p:title="The Ruby Programming Language"
              p:author="David Flanagan & Yukihiro Matsumoto" p:pages="250" />
        <bean class="org.kodejava.spring.core.el.Book" p:title="Einstein" p:author="Walter Isaacson" p:pages="1000" />
    </util:list>

    <bean id="lib1" class="org.kodejava.spring.core.el.Library">
        <property name="books" value="#{books.?[pages gt 250]}" />
    </bean>

    <bean id="lib2" class="org.kodejava.spring.core.el.Library">
        <property name="books" value="#{books.^[pages gt 250]}" />
    </bean>

    <bean id="lib3" class="org.kodejava.spring.core.el.Library">
        <property name="books" value="#{books.$[pages gt 250]}" />
    </bean>

</beans>

The first thing that you can see in the configuration above is the <util-list> where we create a list of Book beans. Next we have three beans definition of the type Library where the books property was assigned with a collection of beans selected from the books list.

The lib1 will contains books that have pages more than 250. The lib2 will contains the first book found to have more than 250 pages while the lib3 will contains the last book found to have more than 250 pages.

Below is the code that will run our configuration file and the example output it will produce.

package org.kodejava.spring.core.el;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpELFilterCollection {
    public static void main(String[] args) {
        try (ClassPathXmlApplicationContext context =
                     new ClassPathXmlApplicationContext("spel-filter-collection.xml")) {

            System.out.println("Library 1");
            Library lib1 = (Library) context.getBean("lib1");
            for (Book book : lib1.getBooks()) {
                System.out.println("    Book = " + book);
            }

            System.out.println("Library 2");
            Library lib2 = (Library) context.getBean("lib2");
            for (Book book : lib2.getBooks()) {
                System.out.println("    Book = " + book);
            }

            System.out.println("Library 3");
            Library lib3 = (Library) context.getBean("lib3");
            for (Book book : lib3.getBooks()) {
                System.out.println("    Book = " + book);
            }
        }
    }
}

Library 1
    Book = Book{title='Essential C# 4.0', author='Michaelis', pages=450}
    Book = Book{title='User Stories Applied', author='Mike Cohen', pages=268}
    Book = Book{title='Einstein', author='Walter Isaacson', pages=1000}
Library 2
    Book = Book{title='Essential C# 4.0', author='Michaelis', pages=450}
Library 3
    Book = Book{title='Einstein', author='Walter Isaacson', pages=1000}

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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How do I read system environment variables in Spring EL?

By I Wayan Saryada in Spring Core 3 Comments

Previously you have seen that we can load properties file and read a value from it in this example: How do I read a value from properties file using Spring EL?. In this example you will learn how to read a special properties available to Spring EL. These properties include the systemEnvironment and systemProperties.

The systemEnvironment property contains all the environment variables on the machine where the program is running. Meanwhile, the systemProperties contains all the properties that we set in Java when the application started, using the -D argument. Let’s see how to access both of these properties in the following Spring configuration 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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="program1" class="org.kodejava.spring.core.el.Program">
        <property name="logPath" value="#{systemProperties['APP.LOG_PATH']}" />
    </bean>

    <bean id="program2" class="org.kodejava.spring.core.el.Program">
        <property name="logPath" value="#{systemEnvironment['TEMP']}" />
    </bean>

</beans>

In the configuration above we have two beans of Program. We set the logPath properties using a different property source. In the program1 bean we use systemProperties['APP.LOG_PATH']. Using this method the value will be pass to our program using the -DAPP.LOG_PATH=F:\Temp when we are executing the program. While the program2 bean’s logPath is read from TEMP directory property available through the systemEnvironment variables.

To make the Spring configuration works you’ll need the Program class. So here is the class definition.

package org.kodejava.spring.core.el;

public class Program {
    private String logPath;

    public Program() {
    }

    public String getLogPath() {
        return logPath;
    }

    public void setLogPath(String logPath) {
        this.logPath = logPath;
    }
}

Finally, let’s create a simple class to execute the Spring configuration file above and see the result of the code.

package org.kodejava.spring.core.el;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpELEnvironment {
    public static void main(String[] args) {
        try (ClassPathXmlApplicationContext context =
                     new ClassPathXmlApplicationContext("spel-environment.xml")) {

            Program program1 = (Program) context.getBean("program1");
            System.out.println("program.getLogPath() = " + program1.getLogPath());

            Program program2 = (Program) context.getBean("program2");
            System.out.println("program.getLogPath() = " + program2.getLogPath());
        }
    }
}

The code will print the following result:

program.getLogPath() = F:\Temp
program.getLogPath() = C:\Users\wsaryada\AppData\Local\Temp

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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How do I read a value from properties file using Spring EL?

By I Wayan Saryada in Spring Core 4 Comments

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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How do I access Map element using Spring EL?

By I Wayan Saryada in Spring Core 0 Comment

In the previous example, How do I access collections members using Spring EL?, you have seen how to access a member of a collection using Spring EL square-braces [] operator. In this post you will learn how to use the same operator to access an element of a Map object.

For demonstration, we will use the same Book class in the previous example to create the bean. The class without the corresponding getters and setters is as follows:

package org.kodejava.spring.core.el;

public class Book {
    private Long id;
    private String title;
    private String author;
    private String type;

    // Getters & Setters
}

Next, let’s create the spring configuration file. In this configuration file we create a map using the <util:map> with the map id of books and add some key-value pair entries in the map.

<?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" 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 http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">

    <util:map id="books">
        <entry key="0-201-61622-X" value="The Pragmatic Programmer" />
        <entry key="978-1-934356-56-2" value="Hello, Android" />
        <entry key="978-1-933988-69-6" value="Secret of The JavaScript Ninja" />
        <entry key="978-1-449-37017-6" value="Java EE 7 Essentials" />
        <entry key="9781935182962" value="Spring Roo in Action" />
    </util:map>

    <bean id="book1" class="org.kodejava.spring.core.el.Book" p:title="#{books['9781935182962']}" />
    <bean id="book2" class="org.kodejava.spring.core.el.Book" p:title="#{books['978-1-933988-69-6']}" />

</beans>

After defining the map, you can see how we access an element of the map. We use the square-braces operator [], we use the same operator as we are accessing a collection member. But instead of passing the index to the operator we pass the key of the map element that we are going to read.

<bean id="book2" class="org.kodejava.spring.core.el.Book" p:title="#{books['978-1-933988-69-6']}"/>

Finally, to run the configuration you’ll need to create the following class:

package org.kodejava.spring.core.el;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpELMapExample {
    public static void main(String[] args) {
        try (ClassPathXmlApplicationContext context =
                     new ClassPathXmlApplicationContext("spel-map.xml")) {

            Book book1 = (Book) context.getBean("book1");
            Book book2 = (Book) context.getBean("book2");

            System.out.println("book1.getTitle() = " + book1.getTitle());
            System.out.println("book2.getTitle() = " + book2.getTitle());
        }
    }
}

And example of output produced by this code can be seen below:

book1.getTitle() = Spring Roo in Action
book2.getTitle() = Secret of The JavaScript Ninja

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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How do I access collections members using Spring EL?

By I Wayan Saryada in Spring Core 0 Comment

In this post you will see another powerful examples of Spring EL. We are going to demonstrate how to use Spring EL to access collection members.

By using Spring EL you can select a single reference member of a collection. You can also select members of collection based on the values of their properties. Another thing you can do is extract properties out of the collection members to create another collection object.

To demonstrate this we are going to create a simple bean / pojo as our collection object. We will create a Book class with some properties (id, title, author).

package org.kodejava.spring.core.el;

public class Book {
    private Long id;
    private String title;
    private String author;
    private String type;

    // Getters & Setters
}

Next, we need to create the spring configuration file. In this configuration we will create a collection of books using the <util:list> element. And we also create a bean with its properties is obtained from one of the collection objects.

<?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" 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 http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">

    <util:list id="books">
        <bean class="org.kodejava.spring.core.el.Book" p:title="Essential C# 4.0" p:author="Michaelis" />
        <bean class="org.kodejava.spring.core.el.Book" p:title="User Stories Applied" p:author="Mike Cohen" />
        <bean class="org.kodejava.spring.core.el.Book" p:title="Learning Android" p:author="Marco Gargenta" />
        <bean class="org.kodejava.spring.core.el.Book" p:title="The Ruby Programming Language"
              p:author="David Flanagan & Yukihiro Matsumoto" />
        <bean class="org.kodejava.spring.core.el.Book" p:title="Einstein" p:author="Walter Isaacson" />
    </util:list>

    <bean id="book" class="org.kodejava.spring.core.el.Book">
        <property name="title" value="#{books[3].title}" />
        <property name="author" value="#{books[3].author}" />
    </bean>

</beans>

In the configuration above you have seen how we set the title and author of the book bean. We use the square-braces operator ([]) to access collection’s member by their index. It’s look like this:

<property name="title" value="#{books[3].title}"/>
<property name="author" value="#{books[3].author}"/>

Which can be read as: please give me the collection object at index number 3 and take the value of its title and author to be assigned to the book bean. And as you might already know that a collection object in Java is always zero-based index. So this will give us the book with title “The Ruby Programming Language”.

And finally let’s create an example class that run our spring configuration above. It’s simply load the spell-collection.xml configuration we create above. Get a bean from the loaded ApplicationContext and print out its properties, title and author properties.

package org.kodejava.spring.core.el;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class SpELCollectionExample {
    public static void main(String[] args) {
        try (ClassPathXmlApplicationContext context =
                     new ClassPathXmlApplicationContext("spel-collection.xml")) {

            Book book = (Book) context.getBean("book");
            System.out.println("book.getTitle() = " + book.getTitle());
            System.out.println("book.getAuthor() = " + book.getAuthor());
        }
    }
}

Executing the code above will give you the following result:

book.getTitle() = The Ruby Programming Language
book.getAuthor() = David Flanagan & Yukihiro Matsumoto

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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