Using Java to find version and start PostgreSQL

You can also find the version of the server using DatabaseMetaData. It has helper methods for getting information about the server. getDatabaseProductVersion(), getDatabaseMajorVersion(), getDatabaseMinorVersion() will give you the database server version.

If PG_VERSION is edited the server won't start. Don't do that. In general, the PostgreSQL data-dir is off limits for direct editing.

At run-time you can use SELECT version() to get the version of the running server.

The server can be started and stopped with pg_ctl. You can check the version of the server binaries whether or not the server is running postgres --version or pg_ctl --version.

The location of the binaries and datadir is something you can control in terms of how you install the server.

Running the query : select version()
would give you the exact version of the posgresql

You can also use DatabaseMetaData interface. It's much more general, not only for postgreSQL and gives you much more than just the database version. Here's an example on how to use it:

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.DatabaseMetaData;
import java.sql.SQLException;

/**
 * @author Binyamin Regev on on 30/11/2016.
 * @version 1.0
 * @since 1.8
 */

public class DatabaseMetaDataHelper {

    static Connection connection = null;
    static DatabaseMetaData metadata = null;


    public DatabaseMetaDataHelper() throws SQLException{

        boolean success = initJDBCDriver();
        if (!success) { throw new SQLException("INIT JDBC DRIVER FAILED!"); }

        success = connectToDatabase();
        if (!success) { throw new SQLException("Connect to database FAILED"); }

        connection = databaseConnection.getConnection();

        try {
            metadata = databaseConnection.getConnection().getMetaData();
        } catch (SQLException e) {
            System.err.println("There was an error getting the metadata: " + e.getMessage());
            e.printStackTrace();
        }
    }

    public boolean initJDBCDriver() {
        try {
            Class.forName("org.postgresql.Driver");
        } catch (ClassNotFoundException e) {
            System.out.println("Where is your PostgreSQL JDBC Driver? Include in your library path!");
            e.printStackTrace();
            return false;
        }

        System.out.println("PostgreSQL JDBC Driver Registered!");
        return true;
    }

    public boolean connectToDatabase() {
        try {
            connection = DriverManager.getConnection(
                    "jdbc:postgresql://127.0.0.1:5432/postgres",
                    "postgres",
                    "admin");

        } catch (SQLException e) {
            System.out.println("Connection Failed! Check output console");
            e.printStackTrace();
            return false;
        }

        if (connection == null) {
            System.out.println("Failed to make connection!");
            return false;
        }

        System.out.println("You made it, take control your database now!");
        return true;
    }

    public static Connection getConnection() {
        return connection;
    }

    public static String getDatabaseProductName() {
        try {
            return metadata.getDatabaseProductName();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    public static String getDriverName() {
        try {
            return metadata.getDriverName();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    public static String getUserName() {
        try {
            return metadata.getUserName();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    public static String getDatabaseProductVersion() {
        try {
            return metadata.getUserName();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    public static String getDriverVersion() {
        try {
            return metadata.getDriverVersion();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    public static String getURL() {
        try {
            return metadata.getURL();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    public static int getDriverMinorVersion() {
        return metadata.getDriverMinorVersion();
    }

    public static int getDriverMajorVersion() {
        return metadata.getDriverMajorVersion();
    }

    public static int getDatabaseMinorVersion() {
        try {
            return metadata.getDatabaseMinorVersion();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return -1;
    }

    public static int getDatabaseMajorVersion() {
        try {
            return metadata.getDatabaseMajorVersion();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return -1;
    }

    public static int getJDBCMajorVersion() {
        try {
            return metadata.getJDBCMajorVersion();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return -1;
    }

    public static int getJDBCMinorVersion() {
        try {
            return metadata.getJDBCMinorVersion();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return -1;
    }

    public static void main(String[] args) {
        try {
            DatabaseMetaDataHelper helper = new DatabaseMetaDataHelper();
            int result = helper.connectToDatabase();

            System.out.println("Database product name = " + getDatabaseProductName());
            System.out.println("Database product version = " + getDatabaseProductVersion());
            System.out.println("Database User name = " + getUserName());
            System.out.println("Driver name = " + getDriverName());
            System.out.println("Driver version = " + getDriverVersion());
            System.out.println("URL = " + getURL());
            System.out.println("Driver major version = " + getDriverMajorVersion());
            System.out.println("Driver minor version = " + getDriverMinorVersion());
            System.out.println("Databse major version = " + getDatabaseMajorVersion());
            System.out.println("Databse minor version = " + getDatabaseMinorVersion());
            System.out.println("JDBC major version = " + getJDBCMajorVersion());
            System.out.println("JDBC minor version = " + getJDBCMinorVersion());

            /*
             * Print all the tables of the database scheme,
             * with their names and structure
             */
            getColumnsMetadata(getTablesMetadata());
        } catch (SQLException e) {
            System.out.println(e.getMessage());
            System.err.println("There was an error retrieving the metadata properties: "+ e.getMessage());
        }
    }
}