- Spring DI Tutorial
- Spring DI - Home
- Spring DI - Overview
- Spring DI - Environment Setup
- Spring DI - IOC Containers
- Spring Dependency Injection
- Spring DI - Create Project
- Constructor Based Injection Examples
- Spring DI - Constructor Based
- Spring DI - Inner Beans Constructor
- Spring DI - Collections Constructor
- Spring DI - Collection Ref Constructor
- Spring DI - Map Constructor
- Spring DI - Map Ref Constructor
- Setter Based Injection Examples
- Spring DI - Setter Based
- Spring DI - Inner Beans Setter
- Spring DI - Collections Setter
- Spring DI - Collection Ref Setter
- Spring DI - Map Setter
- Spring DI - Map Ref Setter
- Autowiring Examples
- Spring DI - Autowiring
- Spring DI - Autowiring ByName
- Spring DI - Autowiring ByType
- Spring DI - Autowiring Constructor
- Factory Method
- Spring DI - Static Factory
- Spring DI - Non-Static Factory
- Spring DI Useful Resources
- Spring DI - Quick Guide
- Spring DI - Useful Resources
- Spring DI - Discussion
Spring DI - Constructor-Based
Constructor-Based DI is accomplished when the container invokes a class constructor with a number of arguments, each representing a dependency on the other class.
Example
The following example shows a class TextEditor that can only be dependency-injected with constructor injection.
Let's update the project created in Spring DI - Create Project chapter. We're adding following files −
TextEditor.java − A class containing a SpellChecker as dependency.
SpellChecker.java − A dependency class.
MainApp.java − Main application to run and test.
Here is the content of TextEditor.java file −
package com.tutorialspoint; public class TextEditor { private SpellChecker spellChecker; public TextEditor(SpellChecker spellChecker) { System.out.println("Inside TextEditor constructor." ); this.spellChecker = spellChecker; } public void spellCheck() { spellChecker.checkSpelling(); } }
Following is the content of another dependent class file SpellChecker.java
package com.tutorialspoint; public class SpellChecker { public SpellChecker(){ System.out.println("Inside SpellChecker constructor." ); } public void checkSpelling() { System.out.println("Inside checkSpelling." ); } }
Following is the content of the MainApp.java file.
package com.tutorialspoint; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class MainApp { public static void main(String[] args) { ApplicationContext context = new ClassPathXmlApplicationContext("applicationcontext.xml"); TextEditor te = (TextEditor) context.getBean("textEditor"); te.spellCheck(); } }
Following is the configuration file applicationcontext.xml which has configuration for the constructor-based injection −
<?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-3.0.xsd"> <!-- Definition for textEditor bean --> <bean id = "textEditor" class = "com.tutorialspoint.TextEditor"> <constructor-arg ref = "spellChecker"/> </bean> <!-- Definition for spellChecker bean --> <bean id = "spellChecker" class = "com.tutorialspoint.SpellChecker"></bean> </beans>
Output
Once you are done creating the source and bean configuration files, let us run the application. If everything is fine with your application, it will print the following message −
Inside SpellChecker constructor. Inside TextEditor constructor. Inside checkSpelling.
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