[JAVA] Until the use of Spring Data and JPA Part 1

The difficulty of setting is quite high.

I think it's a unique way of writing Spring Framework, but I do and wear Java such as property files and xml files. I think it's quite a beginner killing, so I summarized the use of JPA.

Divide goals

1. 1. What you need just to connect with SQL -Hibernate EntityManager library ・ Spring JDBC library ・ Database driver PostgreSQL or H2 ·Property file -Bean configuration file (xml) JavaConfig is not used this time. Maybe it's going to get confusing

2. In addition, what is required for JPA ・ Spring Data JPA library ・ Entity class -Persistence.xml file (Java EJB function) -Bean configuration file (xml) -Execution class with main method

Check the console to see if the query arrived in the database. Use on the web later.

Connection with DB

Library and driver settings

pom settings.

Add to pom and add dependencies. I'm using Spring IO pratform, so I won't describe the version!

pom.xml

		<!-- Hibernate -->
		<dependency>
			<groupId>org.hibernate</groupId>
			<artifactId>hibernate-entitymanager</artifactId>
		</dependency>

		<!-- jdbc -->
		<dependency>
			<groupId>org.springframework</groupId>
			<artifactId>spring-jdbc</artifactId>
		</dependency>
		
		<!-- postgresql database -->
		<dependency>
   			 <groupId>org.postgresql</groupId>
    		<artifactId>postgresql</artifactId>
		</dependency>

After drawing, right click ** Maven → updateProject **

Creating a property file

I will give Spring information about the PostgreSQL driver. Create a property file of ** database.properties ** in src / main / resource.

database.properties

jdbc.driverClassName=org.postgresql.Driver
jdbc.url=jdbc:postgresql://localhost:5432/sample
jdbc.username=postgres
jdbc.password=password

If it's PostgreSQL, it looks like this, according to the DB you use.

Creating a bean configuration file

Register the DataSource and JdbcTemplate in the DI container. Create ** bean.xml ** in src / main / resource

You read the value from the property file and register it in the bean.

• Do not handwrite this kind of thing. Right-click and select ** New → Other ** and select ** Spring → Spring Bean Configuration File ** to select the XML namespace in Wizard format. This time I chose beans context jdbc tx (transaction)

bean.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"
	xmlns:jdbc="http://www.springframework.org/schema/jdbc"
	xmlns:tx="http://www.springframework.org/schema/tx"
	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
		http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc.xsd
		http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd">


	<!--Settings for embedded database>
	<jdbc:embedded-database id="dataSource" type="H2">
		<jdbc:script location="classpath:script.sql"/>
	</jdbc:embedded-database-->

	<!--Setting database properties-->
	<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
	  	<property name="location" value="database.properties" />
	</bean>

	<!--Settings for DB connection-->
	<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource" >
		<property name="driverClassName" value="${jdbc.driverClassName}" />
		<property name="url" value="${jdbc.url}" />
		<property name="username" value="${jdbc.username}" />
		<property name="password" value="${jdbc.password}" />
	</bean>

	<!--Creating a JDBC template bean-->
	<bean class="org.springframework.jdbc.core.JdbcTemplate">
		<constructor-arg ref="dataSource" />
	</bean>

Try to actually connect

Let's take this out of DI and run it Access the database with ** execute ** and ** queryForList ** of JdbcTemplate!

App.java

@Component
@ComponentScan
public class App {
	//private static JdbcTemplate jdbcTemplate;
	private static ApplicationContext context;
	private static JdbcTemplate jdbcTemplate;
	
	public static void main(String args[]) {
		
		//Creating a template using annotations
		//context = new AnnotationConfigApplicationContext(DataSourceConfig.class);
		//JdbcTemplate jdbcTemplate = (JdbcTemplate)context.getBean(JdbcTemplate.class);
		//Get context
		context = new ClassPathXmlApplicationContext("bean.xml");
		jdbcTemplate = context.getBean(JdbcTemplate.class);
	
		List<Map<String, Object>> list = jdbcTemplate
				.queryForList("SELECT * FROM mytable");
		
		for(Map<String, Object> obj : list) {
			System.out.println(obj);
		}
	
	}

}

Do this and watch

At the bottom you can see that the columns have been retrieved from the database.

Continued to Part 2