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We can inject dependencies through the constructor. <bean> <constructor-arg>Sub-elements are used for constructor injection. Here, we need to inject
Original and string-based values Subordinate objects (including objects) Collection values, etc.
Let's take a look at simple examples of injecting original values and string-based values. We have created three files here:
Employee.java applicationContext.xml Test.java
Employee.java
This is a simple class that contains two fields id and name. This class has four constructors and one method.
package com.w;3codebox;
public class Employee {
private int id;
private String name;
public Employee() { System.out.println("def cons"); }
public Employee(int id) { this.id = id; }
public Employee(String name) { this.name = name; }
public Employee(int id, String name) {
this.id = id;
this.name = name;
}
void show() {
System.out.println(id+" "+name);
}
}
applicationContext.xml
We provide information to the Bean through this file. constructor-The arg element calls the constructor. In this case, the parameterized constructor of the int type will be called. Constructor-The value attribute of the arg element assigns the specified value. The type attribute specifies that the int parameter constructor will be called.
<?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-3.0.xsd"> <bean id="e" class="com.w3codebox.Employee"> <constructor-arg value="10" type="int"></constructor-arg> </bean> </beans>
Test.java
This class retrieves Beans from applicationContext.xml file and calls the show method.
package com.w;3codebox;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.xml.XmlBeanFactory;
import org.springframework.core.io.*;
public class Test {
public static void main(String[] args) {
Resource r = new ClassPathResource("applicationContext.xml");
BeanFactory factory = new XmlBeanFactory(r);
Employee s = (Employee)factory.getBean("e");
s.show();
}
}
Output: 10Empty
If you do not specify the type attribute in the constructor arg element, the string type constructor will be called by default.
.... <bean id="e" class="com.w3codebox.Employee"> <constructor-arg value="10></constructor-arg> </bean> ....
If the bean element is changed as described above, the string parameter constructor will be called, and the output will be 0 10.
Output: 0 10
You can also pass string literals as shown below:
.... <bean id="e" class="com.w3codebox.Employee"> <constructor-arg value="Sonoo"></constructor-arg> </bean> ....
Output: 0 Sonoo
You can pass integer literals and string literals in the following ways
.... <bean id="e" class="com.w3codebox.Employee"> <constructor-arg value="10" type="int"></constructor-arg> <constructor-arg value="Sonoo"></constructor-arg> </bean> ....
Output: 10 Sonoo