The JdbcTemplate class provides various methods to execute queries and manipulate the query results. Depending on the query and the expected result type, we can choose from the following three types of objects that can be returned from a JdbcTemplate query:

A . Generic Maps

This is true because the JdbcTemplate.queryForList method returns a List of Map objects, where each Map represents a row of the query result. The Map keys are the column names and the Map values are the column values1. For example:

List<Map<String, Object>> results = jdbcTemplate.queryForList(''SELECT * FROM EMPLOYEE''); for (Map<String, Object> row : results) { System.out.println(row.get(''NAME'') + ' ' + row.get(''SALARY'')); }

B . Simple types (int, long, String, etc)

This is true because the JdbcTemplate.queryForObject method can return a single value of a simple type, such as int, long, String, etc. This method is useful for running queries that return a single row and a single column2. For example:

int count = jdbcTemplate.queryForObject(''SELECT COUNT(*) FROM EMPLOYEE'', Integer.class); System.out.println('Number of employees: ' + count);

D . User defined types

This is true because the JdbcTemplate.query method can return a List of user defined types, such as custom classes or beans. This method takes a RowMapper as an argument, which is an interface that maps each row of the query result to an instance of the user defined type3. For example:

public class Employee { private String name; private int salary; // getters and setters }

public class EmployeeRowMapper implements RowMapper<Employee> { @Override public Employee mapRow(ResultSet rs, int rowNum) throws SQLException { Employee employee = new Employee(); employee.setName(rs.getString(''NAME'')); employee.setSalary(rs.getInt(''SALARY'')); return employee; } }

List<Employee> employees = jdbcTemplate.query(''SELECT * FROM EMPLOYEE'', new EmployeeRowMapper()); for (Employee employee : employees) { System.out.println(employee.getName() + ' ' + employee.getSalary()); }

Spring Security is a framework that provides comprehensive security services for Java applications, such as authentication, authorization, encryption, session management, and more. One of its features is method security, which allows applying access control rules at the method level using annotations or XML configuration. Another feature is authentication, which is the process of verifying the identity of a user or a system. Spring Security supports various authentication mechanisms, such as username and password, tokens, certificates, etc., and can access authentication data from different sources, such as databases, LDAP directories, in-memory stores, etc.

The @Value annotation can be used to inject values from external sources into fields, constructor parameters, or method parameters. To inject a system property, the annotation can use either the ${...} placeholder syntax or the #{...} SpEL expression syntax. The former is simpler and more concise, while the latter is more powerful and flexible. Both syntaxes can access the systemProperties map, which contains all the system properties as key-value pairs.

The @Component annotation indicates that a class is a candidate for auto-detection by Spring and can be registered as a bean in the application context. However, to enable this feature, the Java configuration class must also have the @ComponentScan annotation, which tells Spring where to look for annotated components.

This is true because the id/name of a bean declared by the @Bean annotation is derived from the name of the method that returns the bean. In this case, the method name is clientService, so the bean name will be clientService as well. By default, Spring uses a lower-case first letter for bean names, unless explicitly specified otherwise by using the name attribute of the @Bean annotation. For example, we can use @Bean(name = ''ClientService'') to change the bean name to ClientService (starting with uppercase ''C'').