Template Method Pattern — Spring's JdbcTemplate
Fast recall
Quick revision
Core answer
Understanding of inversion of control within a class hierarchy and boilerplate elimination
Overusing Template Method by making every step abstract — this creates rigid hierarchies that are hard to extend
Contrast the classic subclassing approach with Spring's callback-based Template Method, and mention RestTemplate and TransactionTemplate as other examples
Interview-ready guide
Interview answer
The Template Method pattern separates the invariant skeleton of an algorithm from the variable steps that change per use case. A base class defines the overall flow and defers specific steps to subclasses or callbacks. The pattern is a form of inversion of control — the framework calls your code, not the other way around.
Spring's JdbcTemplate is the canonical production example. Writing raw JDBC requires acquiring a connection, preparing a statement, binding parameters, executing, iterating the result set, translating exceptions, and closing resources. That's 15 lines of plumbing for 2 lines of business logic. JdbcTemplate encapsulates all of that as the invariant template. You provide only the SQL and a RowMapper lambda that converts each ResultSet row into a domain object.
Spring uses the callback-based variant rather than classical subclassing. RowMapper, ResultSetExtractor, and PreparedStatementSetter are all functional interfaces — lambdas work directly. You don't need a new class for every query, which avoids the rigid hierarchies that classical Template Method can create.
The pattern recurs across Spring. RestTemplate owns the HTTP lifecycle — you provide the URL and response type. TransactionTemplate manages begin/commit/rollback — you provide the business logic as a callback. JmsTemplate handles JMS session management. The common thread: Spring owns the boilerplate, you own the business intent. Understanding this pattern explains why Spring's "Template" classes are named the way they are — they're literal implementations of the GoF Template Method.
Template Method Pattern — Spring's JdbcTemplate
Direct Answer
The Template Method pattern defines the skeleton of an algorithm in a base class and defers specific steps to subclasses or callbacks. JdbcTemplate uses this to handle connection acquisition, statement execution, result mapping, and exception translation — delegating only the SQL and row-mapping logic to the caller via lambda callbacks.
Common Mistakes & Pitfalls
Overusing Template Method by making every step abstract — this creates rigid hierarchies that are hard to extend
Check your understanding
Answer these without looking back at the article.
- How is Template Method different from Strategy? Both defer behavior — what's the key distinction?
- Why does JdbcTemplate translate SQLExceptions to DataAccessExceptions?
- When would you prefer TransactionTemplate over @Transactional?
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