[Mac / Java / Eclipse / PostgreSQL] Connect Java application and database

What to write in this article

-How to connect Java application and database when creating Java application with Eclipse installed on Mac

Characteristics of the person who wrote this article

・ Experience in creating web applications with Rails ・ No experience in creating web applications from scratch with Java

When creating a Rails app, for example

DB configuration command in Rails

rails model User name:String email:String
rails:db mingrate

You can connect automatically by executing.

In contrast, Java apps require you to configure each one yourself.

This time, I wrote this article to study the setting.

Development environment

• I really wanted to connect to the DB placed in the AWS RDS, but this time I connected to the local DB because it did not work.
• The language of Eclipse is English.

Prerequisites

Prepare "User" table in database "sample" The following data is stored in the "User" table

SQL

SELECT * FROM USER;

SQL execution result on pgAdmin

File placement

Place "Sampleapp6.java" to write database connection process in dynamic WEB project "sample"

Code example

Sampleapp6.java

package jp.co.sample;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;

public class Sampleapp6 {
	
	public static void main(String[] args) throws Exception {
		
        String url = "jdbc:postgresql://localhost:5432/sample";
        String user = "sample database user";
        String password = "samle database password";

		
		//Connect to database
		try(Connection conn = DriverManager.getConnection(url,user,password)) {
			
			//Prepare a SELECT statement
			String sql = "SELECT * FROM CUSTOMER";
			PreparedStatement pStmt = conn.prepareStatement(sql);
			
			ResultSet rs = pStmt.executeQuery();
			
			//View results
			while (rs.next()) {
				String id = rs.getString("ID");
				String name = rs.getString("NAME");
				String email = rs.getString("EMAIL");
				
				System.out.println(id + " " + name + " " + email);
			}
			
		} catch (SQLException e) {
			e.printStackTrace();
		}
	};

point

** Apply JDBC driver **

Download the JDBC driver and save it (this time save it to your desktop) https://jdbc.postgresql.org/download.html

Right-click on the "sample" project → select "Properties"

Select "Java Build Path" → Apply the external build path saved on the desktop to "Module path"

Processing execution result

The image below is the Eclipse console I was able to confirm that I was getting the data from the database.

Impressions

In Rails, connecting a database is just a few lines of command. You have to configure all Java yourself.

I researched the DB connection method on the net, but I didn't know which information was correct and felt that it was difficult for me to study by myself.

What to do in the future

How to implement data save / edit / update / delete process in Java application

References

Daigo Kunimoto "Introduction to Servlet & JSP 2nd Edition", Impress Corporation, 2019/03/21 First Edition