Question

Method getResult Table of TipTestservlet creates a two-dimensional Stringarray Resultset representation. However, because these dimensions are pre-defined (seven rows by five columns), the string array cannot store additional rows if we append another tip to the database. Modify TipTestservlet so that it can handle any number of tips from the database. Use techniques shown in Chapter \(8,\) Java Database Connectivity \((\mathrm{JDBC}),\) to create a scrollable Resultset so that you can determine the number of rows in the Resultset and size the string array accordingly.

Short answer

Modify your servlet to use JDBC's scrollable ResultSet to dynamically determine the number of rows and create a string array accordingly.

Step-by-step solution

Import Required Libraries

Before modifying the servlet, ensure that all necessary JDBC libraries and classes such as `java.sql.Connection`, `java.sql.Statement`, `java.sql.ResultSet`, `java.sql.ResultSetMetaData`, and `java.sql.DriverManager` are imported at the top of your Java file. This provides access to the necessary classes for handling the database connection and result sets.

Establish Database Connection

Inside your servlet class, create a method to establish a connection to your database using JDBC. Typically, this involves calling `DriverManager.getConnection()` with the database URL, username, and password. Assign the connection to a `Connection` object.

Create a Scrollable ResultSet

Once the connection is established, create a `Statement` object from the `Connection`. Using this statement object, execute a SQL query to retrieve tips from the database. Create a scrollable `ResultSet` by using the method `createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY)`. This allows you to navigate the ResultSet freely and determine the number of rows.

Determine Number of Rows in ResultSet

Move the cursor to the last row of the `ResultSet` with `rs.last()`. Use `rs.getRow()` to get the total number of rows and store it. This number will be used to dynamically define the size of your two-dimensional string array.

Create and Populate String Array

With the number of rows determined, declare a two-dimensional string array. Use `ResultSetMetaData` to get the column count and set this as the second dimension of the array. Then, iterate over the `ResultSet` starting from the first row and store each row's data in the string array, using loops for row and column indices.

Update getResult Method

Modify the `getResult` method of your `TipTestServlet` to return the dynamically sized two-dimensional string array. Ensure that the `Connection`, `Statement`, and `ResultSet` are closed using `try-catch-finally` blocks to free resources.

Key concepts

ResultSet

In Java Database Connectivity (JDBC), a `ResultSet` is an interface that represents the result of a database query. It acts similarly to a table of data, resulting from executing a query using `Statement` or `PreparedStatement` objects. Each row of a `ResultSet` can hold data about a single item retrieved by the query.

Here are some key points to consider when working with `ResultSet`:

• Data Extraction: You can extract data from a `ResultSet` using accessor methods like `getString()`, `getInt()`, and others depending on the type of data stored in each column.
• Cursor Navigation: The cursor (essentially a pointer) allows you to move through the rows of the result set in a forward-only direction, unless the `ResultSet` is scrollable.
• Resource Management: A `ResultSet` is a resource-intensive object. It's important to close it after its use to free up database connections and associated resources.

Understanding `ResultSet` is crucial as it forms the backbone of retrieving and manipulating query results in JDBC.

JDBC Libraries

JDBC stands for Java Database Connectivity and is a Java-based API. It allows Java applications to interact with databases using a standard set of methods and protocols. Several libraries and packages come with JDBC, enabling developers to create a connection, send SQL queries, and handle result sets efficiently.

Some essential components of JDBC libraries are:

• Core Packages: Includes `java.sql` and `javax.sql`, which provide fundamental interfaces and classes for JDBC operations like `Connection`, `Statement`, `ResultSet`, and `SQLException`.
• Driver Libraries: JDBC divers are vendor-specific and handle the actual communication between Java applications and the database.
• Utility Classes: Aid in tasks such as loading drivers, setting up connections, and executing SQL commands.

Utilizing JDBC libraries effectively is key to establishing efficient communication between your Java application and the database.

Scrollable ResultSet

A scrollable `ResultSet` is an enhanced version of the typical `ResultSet` in JDBC. It allows much more flexible navigation through the data retrieved from a database query.

Here's what distinguishes a scrollable `ResultSet`:

• Free Navigation: Unlike the default `ResultSet`, which only lets you move forward, a scrollable `ResultSet` allows you to move backward, forwards, or even to a specific row in the result set.
• Types of Scrollable ResultSet: Two types are typically used: `TYPE_SCROLL_INSENSITIVE`, which is not affected by changes in the database, and `TYPE_SCROLL_SENSITIVE`, which reflects changes.
• Concurrency Control: Options such as `CONCUR_READ_ONLY`, for reading data without changing it, and `CONCUR_UPDATABLE`, for modifying data, can be set based on the application's need.

Using a scrollable `ResultSet` is beneficial when working with data sets where dynamic navigation is required, improving the flexibility and responsiveness of applications.

Connection Management

Connection management in JDBC is the process of establishing, managing, and terminating connections between a Java application and a database. It's a critical aspect of using JDBC effectively. Connections are the gateways through which all interactions with the database occur.

Key elements of connection management include:

• Establishing Connections: Typically achieved using `DriverManager.getConnection()` with appropriate URL, username, and password parameters.
• Connection Pooling: A technique that improves performance and resource utilization by reusing a collection of connections rather than opening new ones repeatedly.
• Closing Connections: Important for freeing resources. Connections, Statements, and ResultSets should be closed in reverse order of their creation.
• Handling Exception: Connection management involves handling exceptions gracefully using try-catch-finally constructs to ensure that resources are released properly.

Proper connection management is vital for building scalable, efficient, and reliable database-driven applications.