Nirmal Balasooriya's Blog: November 2018

In this post I'm going to demonstrate different ways of Bean Autowire mechanisms. In Spring framework it provided mainly 5 ways.

constructor : Spring container will look in to Constructor based autowire.
byName : Spring container will look in to bean name matching.
byType : Spring container will look in to bean class type matching
No (by reference) : Spring container will look in to bean reference explicitly.
default-autowire : Spring container will look in to default-autowire type define in Beans tag on Spring configuration.

Lets create small demonstration application to get understand about each and every Autowire type.

Lets create simple maven project I'll provide GrouupId as "com.sample.spring" and artifactID as "SpringAutowireSamples". Then click on finish.

Then lets add our spring dependencies in to our pom file by updating pom file as bellow.

<groupId>com.sample.spring</groupId>

<artifactId>SpringAutowireSamples</artifactId>

<version>0.0.1-SNAPSHOT</version>

<properties>

<spring_version>5.1.2.RELEASE</spring_version>

</properties>

<dependencies>

<dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-core</artifactId>

<version>${spring_version}</version>

</dependency>

<dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-context</artifactId>

<version>${spring_version}</version>

</dependency>

</dependencies>

</project>

Then lets create our bean classes as bellow.

Address.java

package com.sample.spring.bean;

public class Address {

private String line1;

private String line2;

public String getLine1() {

return line1;

}

public void setLine1(String line1) {

this.line1 = line1;

}

public String getLine2() {

return line2;

}

public void setLine2(String line2) {

this.line2 = line2;

}

@Override

public String toString() {

return "Address [line1=" + line1 + ", line2=" + line2 + "]";

}

Country.java

package com.sample.spring.bean;

public class Country {

private String cntryName;

private String cntryCode;

public String getCntryName() {

return cntryName;

}

public void setCntryName(String cntryName) {

this.cntryName = cntryName;

}

public String getCntryCode() {

return cntryCode;

}

public void setCntryCode(String cntryCode) {

this.cntryCode = cntryCode;

}

@Override

public String toString() {

return "Country [cntryName=" + cntryName + ", cntryCode=" + cntryCode + "]";

}

Division.java

package com.sample.spring.bean;

public class Division {

private String division;

private String divisionId;

public String getDivision() {

return division;

}

public void setDivision(String division) {

this.division = division;

}

public String getDivisionId() {

return divisionId;

}

public void setDivisionId(String divisionId) {

this.divisionId = divisionId;

}

@Override

public String toString() {

return "Division [division=" + division + ", divisionId=" + divisionId + "]";

}

Name.java

package com.sample.spring.bean;

public class Name {

private String firstName;

private String lastName;

public String getFirstName() {

return firstName;

}

public void setFirstName(String firstName) {

this.firstName = firstName;

}

public String getLastName() {

return lastName;

}

public void setLastName(String lastName) {

this.lastName = lastName;

}

@Override

public String toString() {

return "Name [firstName=" + firstName + ", lastName=" + lastName + "]";

}

Student.java

package com.sample.spring.bean;

import org.springframework.beans.factory.annotation.Autowired;

public class Student {

private String stdid;

private int age;

@Autowired

Name stdName;

@Autowired

Country country;

@Autowired

Address address;

Division division;

public Student(String stdid, int age,Division division) {

super();

this.stdid = stdid;

this.age = age;

this.division = division;

}

public String getStdid() {

return stdid;

}

public void setStdid(String stdid) {

this.stdid = stdid;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

@Override

public String toString() {

return "Student [ \n"

+ "stdid=" + stdid + ", \n"

+ "age=" + age + ", \n"

+ "stdName=" + stdName + ", \n"

+ "Country=" + country + ", \n"

+ "Division=" + division + ", \n"

+ "address=" + address + "\n]";

}

Then lets create our spring configuration file with following content. We have to put this configuration file on resources folder in our project.

spring-config.xml

<?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:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd" default-autowire="byType">

<context:annotation-config/>

</bean>

</bean>

</bean>

</bean>

</bean>

<constructor-arg name="stdid" value="std0001"/>

<constructor-arg name="age" value="12"/>

<constructor-arg name="division" ref="divi"/>

</bean>

</beans>

Then lets create our spring loder and load the student bean from there.

MainClass.java

package com.sample.spring;

import org.springframework.context.support.AbstractApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.sample.spring.bean.Student;

public class MainClass {

public static void main(String[] args) {

AbstractApplicationContext context = new ClassPathXmlApplicationContext("spring-config.xml");

Student student=(Student)context.getBean("student");

System.out.println(student);

context.close();

}

Then if we have to do maven install and run this MainClass.java class then we should get following out put.

Student [

stdid=std0001,

age=12,

stdName=Name [firstName=Nirmal, lastName=Balasooriya],

Country=Country [cntryName=Sri Lanka, cntryCode=LK],

Division=Division [division=Excellent, divisionId=EX],

address=Address [line1=adress 1 line 1, line2=adress 1 line 2]

]

This sample contains all of above mentioned Autowire mechanisms. Lets see each in more detail manner.

Constructor Autowire

In the student bean creation Spring container will invoke following bean definition in spring configuration file.

<constructor-arg name="stdid" value="std0001"/>

<constructor-arg name="age" value="12"/>

<constructor-arg name="division" ref="divi"/>

</bean>

As we can see our student have the stdId as "srd0001" , age as "12" and also Division as "Excellent". Here division loading has been done on different manner it will described on next step.

Student [

stdid=std0001,

age=12,

stdName=Name [firstName=Nirmal, lastName=Balasooriya],

Country=Country [cntryName=Sri Lanka, cntryCode=LK],

Division=Division [division=Excellent, divisionId=EX],

address=Address [line1=adress 1 line 1, line2=adress 1 line 2]

]

No (by reference) Autowire

In the Division object instantiation you can see we did not used the @Autowire annotation in the student class but on the Student bean definition we have pass the constructor argument with ref.

</bean>

<constructor-arg name="stdid" value="std0001"/>

<constructor-arg name="age" value="12"/>

<constructor-arg name="division" ref="divi"/>

</bean>

Thats how Spring used this no autowire to instantiate the division object in to student table.

ByName Autowire

To demonstrate byName autowire I have added following two bean configurations in to our configuration file.

</bean>

</bean>

If you can see the Student class we gave the Name variable name as stdName so when Spring container do the dependency injection it will look in to bean with that spesific bean name. So because of that we have the firstName as "Nirmal" and lastName as "Balasooriya".

Student [

stdid=std0001,

age=12,

stdName=Name [firstName=Nirmal, lastName=Balasooriya],

Country=Country [cntryName=Sri Lanka, cntryCode=LK],

Division=Division [division=Excellent, divisionId=EX],

address=Address [line1=adress 1 line 1, line2=adress 1 line 2]

]

ByType Autowire

To demonstrate byType autowire I have added following two bean configurations in to our configuration file.

</bean>

Based on the autowire="byType" of Address configuration in configuration file spring container injected address with line1 "adress 1 line 1" and line2 "adress 1 line 2".

Student [

stdid=std0001,

age=12,

stdName=Name [firstName=Nirmal, lastName=Balasooriya],

Country=Country [cntryName=Sri Lanka, cntryCode=LK],

Division=Division [division=Excellent, divisionId=EX],

address=Address [line1=adress 1 line 1, line2=adress 1 line 2]

]

default-autowire

If you carefully see the spring configuration I have added default-autowire in beans tag. Then added Country bean without autowire attribute in the bean definition but in our out put Spring container injected the Country using this default-autowire configuration.

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xmlns:context="http://www.springframework.org/schema/context"

xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context.xsd" default-autowire="byType">

</bean>

In the out put default-autowire used to provide Country values cntryName as "Sri Lanka" and cntryCode as "LK".

Student [

stdid=std0001,

age=12,

stdName=Name [firstName=Nirmal, lastName=Balasooriya],

Country=Country [cntryName=Sri Lanka, cntryCode=LK],

Division=Division [division=Excellent, divisionId=EX],

address=Address [line1=adress 1 line 1, line2=adress 1 line 2]

]

In this post I'm going to setup Spring Boot web project and do small code demonstration for understanding the structure of the project as well as deploying in to Tomcat as war.

Prerequisites

You should have install java 1.8 or above.
You should have Eclipse installed in your PC.
Your PC should setup Maven installed and configured.

Lets create the maven project on Eclipse go to File -> New -> Maven Project then tick on Creat a simple project and click next. (As show in bellow figure)

Then provide Group Id and Artifact Id and change the packaging as war as show in bellow figure. Then click on finish.

Then change the project JRE to JDK on Java Build Path on the project.

The main advantage on SpringBoot is its reduces lots of development time and increases productivity. In order to use SpringBoot with Hibernate we have to add required dependencies as show in bellow on pom.xml.

<groupId>com.springboot.sample</groupId>

<artifactId>SpringBootWeb</artifactId>

<version>0.0.1-SNAPSHOT</version>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-parent</artifactId>

<version>2.0.5.RELEASE</version>

</parent>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-web</artifactId>

</dependency>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-starter-data-jpa</artifactId>

</dependency>

<groupId>javax.servlet</groupId>

</dependency>

<groupId>org.apache.tomcat.embed</groupId>

<artifactId>tomcat-embed-jasper</artifactId>

<scope>provided</scope>

</dependency>

<groupId>mysql</groupId>

<artifactId>mysql-connector-java</artifactId>

</dependency>

</dependencies>

<build>

<groupId>org.springframework.boot</groupId>

<artifactId>spring-boot-maven-plugin</artifactId>

</plugin>

<finalName>SpringBootWeb</finalName>

</plugins>

</build>

</project>

Spring Boot allows developers to configure their application using a configuration file named application.properties. This configuration file should put in the src/main/resource folder. For our application we use following configurations on application.properties file.

spring.mvc.view.prefix: /WEB-INF/jsp/

spring.mvc.view.suffix: .jsp

application.message: Hello world

#==== connect to mysql ======#

spring.jpa.hibernate.ddl-auto=update

spring.datasource.url=jdbc:mysql://localhost:3306/sample?useSSL=false

spring.datasource.username=root

spring.datasource.password=

spring.datasource.driver-class-name=com.mysql.jdbc.Driver

spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.MySQL5Dialect

Configuration file content

Then lets create simple table on MySQL using following SQL.

-- Table structure for table `country`

DROP TABLE IF EXISTS `country`;

CREATE TABLE `country` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`name` varchar(250) NOT NULL,

`code` varchar(10) NOT NULL,

PRIMARY KEY (`id`)

)

Then add following countries in to table.

-- Dumping data for table `country`

INSERT INTO `country` (`id`, `name`, `code`) VALUES

(1, 'Sri Lanka', 'SL'),

(2, 'Singapore', 'SG'),

(3, 'India', 'IN');

COMMIT;

Then lets try to load these countries on JSP page using Hibernate with SpringBoot.

First of all lets create model class for country as bellow.

package com.sample.springboot.dao.model;

import javax.persistence.Entity;

import javax.persistence.*;

@Entity

@Table(name = "country")

public class Country {

@Id

@GeneratedValue(strategy = GenerationType.AUTO)

@Column(name="id")

private long id;

private String name;

private String code;

public long getId() {

return id;

}

public void setId(long id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getCode() {

return code;

}

public void setCode(String code) {

this.code = code;

}

Then lets create CountryDao interface for country model by using CrudRepository.

package com.sample.springboot.dao;

import org.springframework.data.repository.CrudRepository;

import org.springframework.stereotype.Repository;

import com.sample.springboot.dao.model.Country;

@Repository

public interface CountryDao extends CrudRepository<Country,Long> {

}

Then lets create Controller class to do the URL mapping for "/" which mean when loading our application this controller will tel what application container should do. Lets implement our controller as bellow.

package com.sample.springboot.controller;

import java.util.Map;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.beans.factory.annotation.Value;

import org.springframework.stereotype.Controller;

import org.springframework.web.bind.annotation.GetMapping;

import com.sample.springboot.dao.CountryDao;

import com.sample.springboot.dao.model.Country;

@Controller

public class MyController {

@Autowired

DataSource dataSource;

@Autowired

CountryDao systemRepository;

@Value("${application.message:Hello World}")

private String message;

@GetMapping("/")

public String welcome(Map<String, Object> model) {

String countries="";

Iterable<Country> systemlist = systemRepository.findAll();

System.out.println("here are system count: " + systemlist.toString());

for(Country country:systemlist){

countries+=country.getName()+" ";

System.out.println("Here is a system: " + country.toString());

}

model.put("message", this.message);

model.put("countries", countries);

return "Hello";

}

Then lets add our Hello JSP page in to the application. Accoutering to our configuration file it should be place in webapp/WEB-INF/jsp. Lets add following content in to that. It will simply print two messages "message" and "countries".

<!DOCTYPE html>

<body>

Welcome to Spring Boot JSP page

<br>

Message: ${message}

<br>

List of countries from DB: ${countries}

</body>

</html>

After that lets create our entry point for the web application. Lets Name it as MyApp.java with following contents.

package com.sample.springboot;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.boot.builder.SpringApplicationBuilder;

import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;

import org.springframework.data.jpa.repository.config.EnableJpaRepositories;

@SpringBootApplication

@EnableJpaRepositories("com.sample.springboot")

public class MyApp extends SpringBootServletInitializer{

@Autowired

DataSource dataSource;

@Override

protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {

return application.sources(MyApp.class);

}

public static void main(String[] args) {

SpringApplication.run(MyApp.class, args);

}

So our final project structure will be similar to bellow figure.

Now our application ready to run. Lets create war file by maven install command. Right click on project and go to Run As -> Maven Install.

Then after successful installation you can see SpringBootWeb.war file inside the target folder. Now lets deploy this war file in to Tomcat server. (Place this war file inside the webapps folder on tocat and then start the tomcat server)

When successfully deployed the application you will be able to see similar out put on tomcat console.

Then you can access newly created web application on following URL

http://localhost:8080/SpringBootWeb/ and you should be able to see similar page as bellow figure.

You can access sample project in following GITHUB location.

Nirmal Balasooriya's Blog

Sunday, November 11, 2018

Different Spring Bean Autowire mechanisms

Constructor Autowire

No (by reference) Autowire

ByName Autowire

ByType Autowire

default-autowire

Monday, November 5, 2018

Spring Boot simple web application with MySQL, JPA, Hibernate on Tomcat

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