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Chapter 16: Problem 17

Assume that the following declarations exist: final String DB_URL = "jdbc:derby:CoffeeDB"; String sql = "SELECT = FROM Coffee"; Write code that uses these string objects to get a database connection and execute the SQL statement. Be sure to close the connection when done.

Short Answer

Expert verified
** Answer: The key steps to connect to a database, execute an SQL query, and close the connection using JDBC in Java are: 1. Import the necessary Java packages for working with JDBC. 2. Load the JDBC driver specific to the database being used. 3. Establish a connection to the database using the DriverManager's `getConnection` method and the provided database URL. 4. Create a Statement object from the connection and execute the given SQL query using the statement. 5. Process the data from the ResultSet according to the requirements. 6. Close the statement, ResultSet, and connection resources to ensure proper resource management.

Step by step solution

01

Import necessary packages

First, import the necessary Java packages for working with JDBC. ```java import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; ```
02

Load the JDBC driver

Next, load the JDBC driver for the specific database being used (Derby in this case). Use try-catch block to handle the possible ClassNotFoundException: ```java try { Class.forName("org.apache.derby.jdbc.ClientDriver"); } catch (ClassNotFoundException e) { e.printStackTrace(); } ```
03

Establish the database connection

Using the DriverManager's `getConnection` method, establish a connection to the database using the given DB_URL. Use a try-catch block to handle the possible SQLException: ```java Connection connection = null; try { connection = DriverManager.getConnection(DB_URL); } catch (SQLException e) { e.printStackTrace(); } ```
04

Create a statement and execute the SQL query

Create a Statement object from the connection and then use it to execute the given SQL query. It returns a ResultSet which we can retrieve data from. ```java Statement statement = null; ResultSet resultSet = null; try { statement = connection.createStatement(); resultSet = statement.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); } ```
05

Handle the ResultSet

Loop through the ResultSet and process the data according to your needs. In this example, we will print the data as an illustration. ```java try { while (resultSet.next()) { // Process the data from the ResultSet (e.g., print the data) System.out.println(resultSet.getString("COFFEENAME")); } } catch (SQLException e) { e.printStackTrace(); } ```
06

Close the resources

Finally, close the statement and connection resources in a finally block to ensure they are closed regardless of whether an exception occurred or not. ```java try { if (resultSet != null) { resultSet.close(); } if (statement != null) { statement.close(); } if (connection != null) { connection.close(); } } catch (SQLException e) { e.printStackTrace(); } ``` After following these steps, you will have successfully connected to the database, executed the SQL statement, and closed the connection.

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