Java Full Tutorial
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Java is extremely useful for developing server-side applications that need to interact with other software over HTTP. Many websites use it to display web pages and make them accessible using HTTPS. Since the server-side of any website is the same codebase as the front-end, both sides can work well together without any problem. There are several types of APIs available such as Rest APIs, Spring Boot APIs, MuleAPIs, Python Flask API, etc. All these APIs have their own advantages and disadvantages to implement such services.
The goal of our application will be making some database updates. When creating databases, developers require special knowledge like SQL, JDBC driver, Oracle Database Connectivity Suite (ODBC), MySQL, PostgreSQL, MongoDB, Cassandra Driver, and so many others; each of them takes considerable time and resources. We will use jdbc-4-postgresql as a postgresql driver and other drivers for connecting database tables into the data store. To connect to the local machine database tables, we will use PostgreSQL as a relational database. In addition, there are 3 tables per table: user table, posts table, and users table. This tutorial presents how to install Postgres with PostgreSQL driver.
Step 1: Installing Postgres With PostgreSQL
To start using Postgres, follow these steps:
Create a new Postgres account at your home computer
Download the latest version of Postgres from the official site (it’s not too long)
Choose and install the version and installation option of the Postgres installer in your system
Copy the default file system location and select the appropriate alternative
Now run the Postgres config file in your home folder
Run the pgAdmin4 command to check whether Postgres works properly or not
The Postgres server now starts and provides services to connect to the DB server
Step 2: Create Database Tables
To create a Postgres database table, give the below command:
jdbc -D postgres -D name="PostgresDB" -H hostname="localhost" -P port=5432 -U user="root" -P password=postgres -D user="root password"
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The above command creates tables named PostgresDB, PostgresUser, and PostgresPassword on your computer. You can also name these tables anything you want. For example, our main table called User. We will write down all information of every user in the table (user name). So, enter the following command to do the same thing with PostgresUser. The output table will be PostgresUser table on your computer.
jdbc -D postgres -D name="PostgresDB" -H hostname="localhost" -P port=5432 -U user="root" -P password=postgres -D user="root password"
Step 3: Open Your Postgres Database
Now, open PostgresDB on Windows and Linux systems, and you should see this screen:
Your PostgresDB works perfectly! Now let’s begin the final step, which is installing the required libraries on your operating system and running Postgres.
Step 4: Install Postgres Drivers And Database Connections
This part is very important to use correct Postgres driver and database connection. If you are not using Postgres drivers or database connections, please start from the previous section and go through the next sections. There are already written down the same directions to install drivers properly and set up database connections. But please remember it will take some time to finish installing drivers and finally connect to PostgresDB server. So please provide a backup. I recommend MySQL 5.7 because it can easily connect to PostgresDB. I am talking about MySQL Server instead of MySQL 6.4 but the same instructions with MySQL Server works just fine.
Step 5: Get Started After Setting Up A Postgres DB
To start PostgresDB, please follow these steps:
Connect by using the Postgres shell at PostgresDB by running the following command: pymysql
This will show Postgres shell. From there, let’s begin to create another PostgresDB instance and connect to PostgresDB
Create a new PostgresDB instance by running the command pymysql -h hostname="localhost" -D password="password" -D user="root" -P name="PostgresDB" -H hostname="localhost" -P port=5432 #create a db instance by using the given command.
Creating a New PostgresDB Instance
Let's begin adding a new index in PostgresDB by using the pymysql command.
pymysql -h hostname="localhost" -D index="user" pg_index = "user" -D index="posts" pg_index = "posts"
In the above command, we add two indexes, i.e., the key column called "user" and the value column called "user". We select the unique values in the user column from user table and posts column from posts table. Then, it creates two additional indexes at the end of the user and posts columns. These indexes are called id and id_posts.id. Here is the sample output.
CREATE TABLE IF NOT EXISTS (id DRIVER DEFAULT PRIVILEGE), (id VARCHAR(20), user DOUBLE, posts VARCHAR(20), postid VARCHAR(20)) INSERT INTO TABLE IF NOT EXISTS (user VARCHAR(20), posts VARCHAR(20), userid VARCHAR(20)), (posts VARCHAR(20), postid VARCHAR(20)), users VARCHAR(20), userid VARCHAR(20), postid VARCHAR(20))) INSERT INTO TABLE IF NOT EXISTS (users VARCHAR(20), posts VARCHAR(20), userid VARCHAR(20), postid VARCHAR(20), id VARCHAR(20), ad_id VARCHAR(20), id_posts VARCHAR(20) VARCHAR(30) ) INSERT INTO INDEXES primary t_userID, t_posts t_userID, t_userName, t_posts_posts t_first_postId, t_last_postId, t_userPostId, t_userId, t_posts_posts t_userID_posts, t_userId, t_posts_posts t_posts_users, t_userId, t_postId, t_userPostId, t_posts_Posts t_userID_posts, t_userId_posts, i_userID VARCHAR(20), i_userPostId, i_userPostId, i_userId VARCHAR(20), i_postId, i_posts VARCHAR(20), i_userPostId_posts, i_userPostId, i_userId_posts) INSERT INTO USER_TABLE SELECT * FROM user, posts
Note: PostgresDB keeps track of changes made to its rows, this means if somebody changes something on his/her table, PostgresDB needs to find out where he is moving the record, and this process is called scanning. This particular method is called Insert Statement Scanning.
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To avoid unnecessary calls from PostgresDB, PostgresDB’s behaviour varies, such as, if you write to the table without specifying keys and values, PostgresDB does not notify you about it and leaves the entry intact. To change the existing row, you have to change it manually in a query statement. In addition, if you forget to specify the keys and values when inserting you may face errors in the future. Let me repeat my question again in this section — why should I insert? But there are different types of inserts.
Insert Into Table
Insert Statement
INSERT INTO TABLE User
INSERT INTO PostgresDB PostgresUser
INSERT INTO PostgresDB PostgresUser_Posts
INSERT INTO PostgresDB Postgresuser_Posts_Posts
INSERT INTO PostgresDB Postgresuser_Posts_Posts_Posts SELECT ID FROM users
INSERT INTO Topics
INSERT INTO User_Posts
INSERT INTO User_Posts_Posts
INSERT INTO User_Topics
INSERT INTO User
INSERT INTO Topics
INSERT INTO User_Posts
INSERT INTO User_Posts_Posts
INSERT INTO User_Topics
INSERT INTO Topic
INSERT INTO User_Topics
INSERT INTO User, PostgresUser_Posts
INSERT INTO Postgresuser_Posts_Posts
INSERT INTO Postgresuser_Posts_Posts SELECT ID FROM content_user
INSERT INTO Users
INSERT INTO Postgresuser_Posts
INSERT INTO User_Posts_Posts SELECT ID FROM content_user_posts
INSERT INTO Topics
INSERT INTO User_Posts
INSERT INTO User_Posts_Posts SELECT ID FROM content_user_posts_posts
INSERT INTO Topics_Posts
INSERT INTO Topics_Posts
INSERT INTO Topics_Posts_Posts SELECT ID FROM content_user
INSERT INTO Readers
INSERT INTO Readers_Posts
INSERT INTO Readers_Topics
INSERT INTO Readers
INSERT INTO Consumers
INSERT INTO Consumer
INSERT INTO Consumers
INSERT INTO