c namespace

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1 (p namespace) | 2 (c namespace)

c namespace was introduced in Spring 3.1. Like p namespace is a shortcut notation for <property> tags, c namespace is a shortcut notation for <constructor-arg> tags.

Consider following example:

Student.java

package di.cnamespace;

public class Student {
    private String name;
    private int age;
    private Course course;
  
    //constructor
    Student(String name, int age, Course c){
        this.name = name;
        this.age = age;
        this.course = c;
    }
  
// setters and getters...  

    public void displayInfo(){
        System.out.println("Student Name : "+name);
        System.out.println("Student Age : "+ age);
        System.out.println("Course name : "+course.getCourseName());
    }
}

Course.java

package di.cnamespace;

public class Course {

    String courseName;
  
    Course(String course){
        this.courseName = course;
    }
  
    public void setCourseName(String name){
        this.courseName = name;
      
    }
    public String getCourseName(){
        return courseName;
      
    }
  
}

MainApp.java

package di.cnamespace;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp{
public static void main(String args[]){
  
    ApplicationContext appContext = new ClassPathXmlApplicationContext("resources/ApplicationContext.xml");
    Student stud = (Student)appContext.getBean("student");
    stud.displayInfo();
 }
}

ApplicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="https://www.springframework.org/schema/beans"
xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd">
<bean id="student" class="di.cnamespace.Student">
<constructor-arg value="abc"/>
<constructor-arg value="30"/>
<constructor-arg ref="course1"/>
</bean>

<bean id="course1" class="di.cnamespace.Course">
<constructor-arg value="Computers"/>
</bean>
</beans>

In the above program arguments of Student and Course class constructors have been injected using <constructor-arg> tags.

Now the same program using c namespace is (you only need to change ApplicationContext.xml, other classes remain same):

ApplicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="https://www.springframework.org/schema/beans"
xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
xmlns:c="https://www.springframework.org/schema/c"
xsi:schemaLocation="https://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd">

<bean id="student" class="di.cnamespace.Student" c:name="abc" c:age="30" c:c-ref="course1"/>

<bean id="course1" class="di.cnamespace.Course" c:course="computers"/>
</beans>

In the above program we are using c namespace to inject the argument values of Student and Course class constructors. For example,

c:age="30"  is substitute of:
<constructor-arg value="30"/>

Note how we are injecting reference to other bean as a value for the 'c' argument of Student class constructor, using c namespace:

c:c-ref="course1"
is a substitute of
<constructor-arg ref="course1"/>

Note the -ref at the end of c:c-ref="course1". -ref means this property would accept a reference to other bean as its value.

Unlike <constructor-arg> tags, c namespace are not separate tags but they are the part of <bean> tag

Note that name, age and c in c:name, c:age, c:c-ref respectively are the name of arguments of Student class constructor. They are not the names of Student class member fields/properties which are name, age and course.

For c namespace to work you have to add its schema URI https://www.springframework.org/schema/c in above xml file.

In case when we do not know the names of constructor arguments we can use following syntax in ApplicationContext.xml:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="https://www.springframework.org/schema/beans"
xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
xmlns:c="https://www.springframework.org/schema/c"
xsi:schemaLocation="https://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd">

<bean id="student" class="di.cnamespace.Student" c:_0="abc" c:_1="30" c:_2-ref="course1"/>

<bean id="course1" class="di.cnamespace.Course" c:_0="computers"/>
</beans>

Here c:_0 means first argument of constructor, c:_1 means second argument and c:_2-ref means third argument which is accepting a reference to other bean as its value.

1 (p namespace) | 2 (c namespace)

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