JDBC | Kode Java

How do I export MySQL database schema into markdown format?

By Wayan in JDBC Last modified: March 9, 2023 0 Comment

The following code example demonstrate how to export MySQL database schema into markdown table format. We get the table structure information by executing MySQL’s DESCRIBE statement.

The steps we do in the code snippet below:

Connect to the database.
We obtain the list of table name from the database / schema.
Executes DESCRIBE statement for each table name.
Read table structure information such as field, type, null, key, default and extra.
Write the information into markdown table format and save it into table.md.

And here are the complete code snippet.

package org.kodejava.jdbc;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class DescribeMySQLToMarkDown {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    public static void main(String[] args) {
        String tableQuery = """
                select table_name
                from information_schema.tables
                where table_schema = 'kodejava'
                  and table_type = 'BASE TABLE'
                order by table_name;
                """;

        try (Connection connection = DriverManager.getConnection(URL, USERNAME, PASSWORD)) {
            Statement stmt = connection.createStatement();
            ResultSet resultSet = stmt.executeQuery(tableQuery);
            List<String> tables = new ArrayList<>();
            while (resultSet.next()) {
                tables.add(resultSet.getString("table_name"));
            }

            System.out.println(tables.size() + " tables found.");

            try (BufferedWriter writer = new BufferedWriter(new FileWriter("table.md"))) {
                for (String table : tables) {
                    System.out.println("Processing table: " + table);
                    Statement statement = connection.createStatement();
                    ResultSet descResult = statement.executeQuery("DESCRIBE " + table);

                    writer.write(String.format("Table Name: **%s**%n%n", table));
                    writer.write("| Field Name | Data Type | Null | Key | Default | Extra |\n");
                    writer.write("|:---|:---|:---|:---|:---|:---|\n");
                    while (descResult.next()) {
                        String field = descResult.getString("field");
                        String type = descResult.getString("type");
                        String nullInfo = descResult.getString("null");
                        String key = descResult.getString("key");
                        String defaultInfo = descResult.getString("default");
                        String extra = descResult.getString("extra");
                        String line = String.format("| %s | %s | %s | %s | %s | %s |%n",
                                field, type, nullInfo, key, defaultInfo, extra);
                        writer.write(line);
                    }
                    writer.write("\n<br/>\n<br/>\n");
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

This code snippet will produce something like below. I have tidy up the markdown for a better presentation.

Table Name: **books**

| Field Name | Data Type       | Null | Key | Default | Extra          |
|:-----------|:----------------|:-----|:----|:--------|:---------------|
| id         | bigint unsigned | NO   | PRI | null    | auto_increment |
| isbn       | varchar(30)     | NO   |     | null    |                |

<br/>
<br/>

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.32</version>
</dependency>

How do I create MySQL database programmatically in Java?

By Wayan in JDBC Last modified: March 9, 2023 4 Comments

There are times that you might need to create database or tables right after you run your program instead of manually creating it. In this example I will show you how you can do this using JDBC and MySQL database. The first thing we need to do as usual when creating a JDBC program is to define a JDBC URL. One thing that you’ll notice here is that we don’t define the database name in the URL. So the URL will be like jdbc:mysql://localhost.

After defining the URL we need to create a connection to the database. We issued the DriverManager.getConnection() method and pass the URL, username and password as the arguments. The next step is to create a PreparedStatement. When we call the preparedStatement() method we pass an SQL command to create the database, which is CREATE DATABASE IF NOT EXISTS DEMODB. This will create the database when there is database with DEMODB exists in the database. Finally, call the PreparedStatement‘s execute() method.

Now you can try for your self, start typing the following code snippet in your text editor or IDE and execute it to create the database.

package org.kodejava.jdbc;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;

public class CreateMySQLDatabaseExample {
    public static void main(String[] args) {
        // Defines the JDBC URL. As you can see, we are not specifying
        // the database name in the URL.
        String url = "jdbc:mysql://localhost";

        // Defines username and password to connect to database server.
        String username = "root";
        String password = "";

        // SQL command to create a database in MySQL.
        String sql = "CREATE DATABASE IF NOT EXISTS DEMODB";

        try (Connection conn = DriverManager.getConnection(url, username, password);
             PreparedStatement stmt = conn.prepareStatement(sql)) {

            stmt.execute();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

After you are executing the code snippet above you will find a new database named DEMODB created in your MySQL database server.

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.32</version>
</dependency>

How to establish connection to database with Properties?

By Wayan in JDBC Last modified: March 9, 2023 0 Comment

In the following code snippet you’ll see how to pass some connection arguments when connecting to a database. To do this we can use the java.util.Properties class. We can put some key value pairs as a connection arguments to the Properties object before we pass this information into the DriverManager class.

Let’s see the example below:

package org.kodejava.jdbc;

import java.sql.*;
import java.util.Properties;

public class GetConnectionWithProperties {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    public static void main(String[] args) {
        GetConnectionWithProperties demo = new GetConnectionWithProperties();
        try (Connection connection = demo.getConnection()) {
            // do something with the connection.
            Statement stmt = connection.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT * FROM products");
            while (rs.next()) {
                System.out.println("Code = " + rs.getString("code"));
                System.out.println("Name = " + rs.getString("name"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    private Connection getConnection() throws SQLException {
        Properties connectionProps = new Properties();
        connectionProps.put("user", USERNAME);
        connectionProps.put("password", PASSWORD);

        Connection connection = DriverManager.getConnection(URL, connectionProps);
        System.out.println("Connected to database.");
        return connection;
    }
}

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.32</version>
</dependency>

How to automatically close resources in JDBC?

By Wayan in JDBC Last modified: March 9, 2023 0 Comment

One thing that we need to do manually when programming using JDBC is to make sure to close all the resources that we use. All resources including the ResultSet, Statement and Connection must be closed. This will usually produce a lot of boilerplate code in our program.

Starting from JDBC 4.1 which is a part of Java 7 we can use the try-with-resources statement to automatically manage the resources that we use. This try statement closes the resources used when the block finishes its execution either normally or abruptly.

Here is an example that show us how to use the try-with-resources statement.

package org.kodejava.jdbc;

import java.sql.*;

public class TryWithResourceJdbc {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    public static void main(String[] args) {
        try (Connection conn =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD);
             Statement stmt = conn.createStatement();
             ResultSet rs = stmt.executeQuery("SELECT * FROM products")) {

            while (rs.next()) {
                String code = rs.getString("code");
                String name = rs.getString("name");

                System.out.println("Code: " + code + "; Name: " + name);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.32</version>
</dependency>

How do I retrieve available catalogs in database?

By Wayan in JDBC Last modified: May 27, 2023 0 Comment

The examples below show you how to get the available catalog names in MySQL database. The available catalog names can be obtained from the DatabaseMetaData object by calling the getCatalogs() method. This method returns a ResultSet object. We iterate it and get the schema name by calling the getString() method and pass TABLE_CAT as the column name.

package org.kodejava.jdbc;

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

public class MetadataGetCatalog {
    private static final String URL = "jdbc:mysql://localhost";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Gets DatabaseMetaData
            DatabaseMetaData metadata = connection.getMetaData();

            // Retrieves the schema names available in this database
            ResultSet rs = metadata.getCatalogs();

            while (rs.next()) {
                String catalog = rs.getString("TABLE_CAT");
                System.out.println("Catalog: " + catalog);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Here a list of catalog names available in the MySQL database:

Catalog: kodejava
Catalog: musicdb
Catalog: mysql
Catalog: performance_schema
Catalog: sys

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.33</version>
</dependency>

How do I get the maximum number of concurrent connections?

By Wayan in JDBC Last modified: May 27, 2023 0 Comment

This example show you how to get the maximum number of concurrent connections to a database that are possible. To get this information we use the DatabaseMetaData.getMaxConnections() method call. If return value is zero it means that there is no limit or the limit is unknown.

package org.kodejava.jdbc;

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

public class MaxConnections {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Get database meta data.
            DatabaseMetaData metaData = connection.getMetaData();

            // Retrieves the maximum number of concurrent
            // connections to this database that are possible.
            // A result of zero means that there is no limit or
            // the limit is not known.
            int max = metaData.getMaxConnections();
            System.out.println("Max concurrent connections: " + max);
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.33</version>
</dependency>

How do I check whether a driver is JDBC compliant?

By Wayan in JDBC Last modified: May 27, 2023 0 Comment

package org.kodejava.jdbc;

import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.SQLException;

public class JDBCCompliant {
    private static final String URL = "jdbc:mysql://localhost/kodejava";

    public static void main(String[] args) {
        try {
            Driver driver = DriverManager.getDriver(URL);

            // Check if the driver is a genuine JDBC compliant driver.
            if (driver.jdbcCompliant()) {
                System.out.println("A genuine JDBC compliant driver");
            } else {
                System.out.println("Not a genuine JDBC compliant driver");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.33</version>
</dependency>

How do I get JDBC driver property information?

By Wayan in JDBC Last modified: May 27, 2023 0 Comment

The example below show you how to get the information about the possible properties for the corresponding JDBC driver.

package org.kodejava.jdbc;

import java.sql.*;

public class DriverPropertyInfoDemo {
    private static final String URL = "jdbc:mysql://localhost/kodejava";

    public static void main(String[] args) {
        try {
            // Gets information about the possible properties for this
            // driver.
            Driver driver = DriverManager.getDriver(URL);
            DriverPropertyInfo[] props = driver.getPropertyInfo(URL, null);

            for (DriverPropertyInfo info : props) {
                System.out.println("Name       : " + info.name);
                System.out.println("Description: " + info.description);
                System.out.println("Value      : " + info.value);
                System.out.println("-----------------------------------");

                String[] choices = info.choices;
                if (choices != null) {
                    StringBuilder sb = new StringBuilder("Choices    : ");
                    for (String choice : choices) {
                        sb.append(choice).append(",");
                    }

                    System.out.println(sb);
                }
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

The example result of the code snippet above:

Name       : host
Description: Hostname of MySQL Server
Value      : localhost
-----------------------------------
Name       : port
Description: Port number of MySQL Server
Value      : 3306
-----------------------------------
Name       : dbname
Description: Database name;
Value      : kodejava
-----------------------------------
Name       : user
Description: Username to authenticate as
Value      : null
-----------------------------------
Name       : password
Description: Password to use for authentication
Value      : null
-----------------------------------
Name       : clientCertificateKeyStorePassword
Description: Password for the client certificates key store.
Value      : null
-----------------------------------
Name       : serverRSAPublicKeyFile
Description: File path to the server RSA public key file for sha256_password authentication. If not specified, the public key will be retrieved from the server.
Value      : null
-----------------------------------
Name       : cacheDefaultTimeZone
Description: Caches clients default time zone. This results in better performance when dealing with time zone conversions in Date and Time data types, however it wont be aware of time zone changes if they happen at runtime.
Value      : true
-----------------------------------
Choices    : TRUE,FALSE,YES,NO,
...
...
...

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.33</version>
</dependency>

How do I check if the OUT parameter value is null?

By Wayan in JDBC Last modified: May 27, 2023 0 Comment

This example show you how to use the CallableStatement.wasNull() method call to see if the last OUT parameter has a value of SQL NULL.

package org.kodejava.jdbc;

import java.math.BigDecimal;
import java.sql.Connection;
import java.sql.CallableStatement;
import java.sql.DriverManager;
import java.sql.Types;
import java.sql.SQLException;

public class WasNullExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Prepares a call to the sored procedure
            String query = "call Get_Product_By_Price2(?, ?)";
            CallableStatement cb = connection.prepareCall(query);

            // Sets the input parameter
            cb.setBigDecimal(1, new BigDecimal("50"));

            // Registers the OUT parameter
            cb.registerOutParameter(2, Types.VARCHAR);

            // Executes the query
            cb.executeQuery();

            // Gets the OUT parameter value
            cb.getString(2);

            // Checks if the last OUT parameter has value of SQL NULL.
            // This method should be called only after calling a
            // getter method; otherwise, there is no value to use in
            // determining whether it is null or not.
            if (cb.wasNull()) {
                System.out.println("Product has an SQL NULL value");
            } else {
                System.out.println("Product: " + cb.getString(2));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Here is the stored procedure script we called in the example above.

DELIMITER ;;
DROP PROCEDURE IF EXISTS Get_Product_By_Price2;;
CREATE PROCEDURE Get_Product_By_Price2(
    IN product_price DECIMAL(10, 2),
    OUT product_name VARCHAR(50))
BEGIN
    SELECT NAME
    INTO product_name
    FROM products
    WHERE price = product_price;
END;;
DELIMITER ;

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.33</version>
</dependency>

How do I call a stored procedure that return a result set?

By Wayan in JDBC Last modified: May 27, 2023 0 Comment

This example show you how to call a stored procedure that return a result set of the query execution result.

package org.kodejava.jdbc;

import java.math.BigDecimal;
import java.sql.CallableStatement;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;

public class CallableStatementExample {
    private static final String URL = "jdbc:mysql://localhost/kodejava";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "";

    public static void main(String[] args) {
        try (Connection connection =
                     DriverManager.getConnection(URL, USERNAME, PASSWORD)) {

            // Prepares a call to the sored procedure. This SP takes
            // one IN parameter
            String query = "call Get_Product_By_Price(?)";
            CallableStatement cb = connection.prepareCall(query);

            // Sets the input parameter
            cb.setBigDecimal(1, new BigDecimal("50.99"));

            // Execute the query
            ResultSet rs = cb.executeQuery();

            while (rs.next()) {
                System.out.println("Product: " + rs.getString(1));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

Here is the stored procedure script we use in the example above.

DELIMITER ;;
DROP PROCEDURE IF EXISTS Get_Product_By_Price;;
CREATE PROCEDURE Get_Product_By_Price(IN product_price DECIMAL(10, 2))
BEGIN
    SELECT name FROM products WHERE price = product_price;
END;;
DELIMITER ;

Maven dependencies

<dependency>
    <groupId>com.mysql</groupId>
    <artifactId>mysql-connector-j</artifactId>
    <version>8.0.33</version>
</dependency>