Resource Management: Chained Cleanup with Validation

In this problem, you will create DatabaseConnection and FileWriterSim classes implementing AutoCloseable, adding input validation to their constructors and methods. For invalid arguments, throw IllegalArgumentException; for valid arguments, return the result string. The processQuery and processWrite methods in the Main class manage resources using try-with-resources.

Learning Objective: Implement input validation in AutoCloseable resources and understand exception propagation through try-with-resources

Specifications

DatabaseConnection class

• Implements AutoCloseable
• Constructor DatabaseConnection(String host):
  • If host is null or empty, throw IllegalArgumentException("Host cannot be null or empty")
  • Otherwise store the host in a field
• query(String sql) method:
  • If sql is null or empty, throw IllegalArgumentException("SQL cannot be null or empty")
  • Otherwise return "Result of [" + sql + "] on " + host
• close() method: resource cleanup (no output required)

FileWriterSim class

• Implements AutoCloseable
• Constructor FileWriterSim(String filename):
  • If filename is null or empty, throw IllegalArgumentException("Filename cannot be null or empty")
  • Otherwise store the filename in a field
• write(String data) method:
  • If data is null, throw IllegalArgumentException("Data cannot be null")
  • Otherwise return "Written [" + data + "] to " + filename
• close() method: resource cleanup (no output required)

Main class

• processQuery(String host, String sql) static method:
  • Create a DatabaseConnection using try-with-resources
  • Return the result of db.query(sql)
  • Let exceptions propagate to the caller
• processWrite(String filename, String data) static method:
  • Create a FileWriterSim using try-with-resources
  • Return the result of writer.write(data)
  • Let exceptions propagate to the caller
• main(String[] args) method: program entry point

Test Examples

Call	Result
processQuery("localhost", "SELECT * FROM users")	"Result of [SELECT * FROM users] on localhost"
processWrite("output.txt", "query result")	"Written [query result] to output.txt"
processQuery(null, "SELECT * FROM users")	IllegalArgumentException: Host cannot be null or empty
processQuery("localhost", "")	IllegalArgumentException: SQL cannot be null or empty
processWrite(null, "data")	IllegalArgumentException: Filename cannot be null or empty
processWrite("output.txt", null)	IllegalArgumentException: Data cannot be null