Hibernate / MyBatis Interview questions
1. What is MyBatis?
MyBatis is an open-source Java persistence framework that maps SQL statements to Java methods, letting developers write and control their own SQL directly while MyBatis handles the mechanical work of parameter binding, executing the statement, and mapping the result set back into Java objects. It...
2. What is the purpose of MyBatis?
MyBatis exists to eliminate the repetitive boilerplate of manually working with JDBC — opening connections, preparing statements, binding parameters one by one, iterating a ResultSet, and mapping columns into object fields by hand — while still giving developers full, direct control o...
3. What are the key features of MyBatis?
MyBatis combines a focused set of capabilities aimed specifically at making hand-written SQL easier to work with from Java, without taking over SQL generation the way a full ORM does. Feature What it Provides SQL mapping Maps hand-written SQL statements directly to Java interface methods Dynamic ...
4. What is the difference between MyBatis and Hibernate?
Both are Java persistence frameworks, but they represent fundamentally different philosophies: MyBatis is a SQL mapper that keeps hand-written SQL front and center, while Hibernate is a full object-relational mapping (ORM) framework that generates SQL automatically from an object model. MyBatis H...
5. What is a SqlSessionFactory in MyBatis?
A SqlSessionFactory is the central factory object responsible for creating SqlSession instances, built once from MyBatis's configuration (data source settings, mapper registrations, type handlers) and then reused for the lifetime of the application, rather than being recreated for every database ...
6. What is a SqlSession in MyBatis?
A SqlSession is the primary interface for executing SQL commands, retrieving mappers, and managing transactions in MyBatis, created from a SqlSessionFactory and representing a single, typically short-lived unit of work against the database. try (SqlSession session = sqlSessionFactory.openSession(...
7. What is a Mapper interface in MyBatis?
A Mapper interface is a plain Java interface whose methods correspond to SQL statements defined either in a matching XML mapper file or directly via annotations, and MyBatis automatically generates a working implementation of that interface at runtime — no hand-written implementation class ...
8. What is the mybatis-config.xml file used for?
The mybatis-config.xml file is MyBatis's top-level, global configuration file, holding settings that apply across the entire application — environment/data source configuration, type aliases, plugin registrations, and the list of mapper files or interfaces to load — distinct from the ...
9. What is a Mapper XML file?
A Mapper XML file defines the actual SQL statements for a given mapper namespace, associating each statement with an id that corresponds to a method on the matching Mapper interface, along with the parameter and result type information MyBatis needs to bind inputs and map outputs correctly.
10. How do you write a basic SELECT statement in MyBatis?
A basic SELECT statement in MyBatis is defined inside a
11. What is parameter binding in MyBatis?
Parameter binding is the process of substituting Java method arguments into placeholders within a SQL statement, using the #{} syntax to reference a parameter by name (or by property, for object parameters), which MyBatis translates into a safely parameterized JDBC PreparedStatement.
12. What is result mapping?
Result mapping is the process of translating columns in a SQL query's result set into fields or properties of a Java object, which MyBatis can do automatically for simple cases (matching column names to bean property names) or explicitly via a
13. What are the supported statement types in MyBatis?
MyBatis provides four core XML elements (and their annotation equivalents) corresponding to the standard SQL data manipulation operations, each with slightly different default behaviors around what they return. Element / Annotation SQL Operation Typical Return
14. What is the difference between #{} and ${} in MyBatis?
Both syntaxes substitute a value into a SQL statement, but they work through fundamentally different mechanisms with very different safety implications — a distinction that's one of the most commonly tested MyBatis interview topics for good reason. #{} ${} Compiled as a JDBC PreparedStateme...
15. What is a resultMap?
A resultMap is an explicit, named mapping definition in a Mapper XML file that describes how the columns of a query's result set correspond to the properties of a Java object, used whenever the automatic, name-matching mapping behind a simple resultType isn't sufficient.
16. How do you configure a data source in MyBatis?
In a plain, non-Spring MyBatis application, a data source is configured inside the
17. What is MyBatis-Spring?
MyBatis-Spring is the integration library that lets MyBatis participate cleanly in a Spring application — wiring MyBatis's SqlSessionFactory and mapper beans into the Spring container, and critically, letting MyBatis operations participate in Spring's own transaction management rather than ...
18. How do you integrate MyBatis with Spring Boot?
Integrating MyBatis with Spring Boot typically means adding the mybatis-spring-boot-starter dependency, which brings in MyBatis, MyBatis-Spring, and Spring Boot auto-configuration that wires up a SqlSessionFactory and mapper scanning automatically based on sensible defaults and application proper...
19. What is dynamic SQL in MyBatis?
Dynamic SQL refers to a set of XML elements MyBatis provides for conditionally building a SQL statement's structure at execution time based on which parameters are actually present or what values they hold, rather than needing to write out every possible combination of conditions as separate, har...
20. List the dynamic SQL elements available in MyBatis?
MyBatis provides a specific set of XML tags for building dynamic SQL, each addressing a different conditional or structural need common in real-world queries. Element Purpose
21. What is the difference between MyBatis and JPA/Hibernate in terms of philosophy?
The core philosophical divide is where control over SQL generation sits: JPA/Hibernate treats the object model as the primary artifact and derives SQL from it automatically, while MyBatis treats SQL itself as the primary artifact and maps it explicitly to Java objects. MyBatis JPA/Hibernate "SQL-...
22. Why is #{} preferred over ${} for parameter binding?
#{} is preferred as the default because it compiles down to a JDBC PreparedStatement placeholder, meaning the actual value is sent to the database separately from the SQL statement's structure, which is what fundamentally prevents SQL injection — the database driver treats the bound value p...
23. How does MyBatis prevent SQL injection?
MyBatis itself doesn't actively scan for or block malicious input — its protection comes from encouraging (and defaulting most examples and generated code toward) the #{} parameter binding syntax, which relies on JDBC's own PreparedStatement mechanism to keep SQL structure and data values f...
24. What is the difference between resultType and resultMap?
Both attributes tell MyBatis how to map a query's result set to Java objects, but they differ in how that mapping is expressed: resultType is a shorthand for simple, automatic mapping, while resultMap references an explicit, reusable mapping definition. resultType resultMap Inline attribute namin...
25. What is the @Param annotation used for in MyBatis?
The @Param annotation assigns an explicit name to a Mapper interface method parameter, which is needed whenever a statement takes more than one simple parameter, since #{} placeholders in the SQL need to reference each parameter by a name that Java doesn't otherwise preserve at runtime by default...
26. Explain how MyBatis handles one-to-many mappings?
A one-to-many relationship — like one order having many line items — is expressed in a resultMap using the
27. Explain how MyBatis handles many-to-one mappings?
A many-to-one relationship — like many orders each belonging to one customer — is expressed using the
28. What is the difference between association and collection in resultMap?
Both elements map a nested, related object within a parent resultMap, but they differ in cardinality — exactly matching the distinction between a many-to-one/one-to-one relationship and a one-to-many relationship. association collection Maps a single nested object. Maps a list (or other col...
29. What is lazy loading in MyBatis, and how do you configure it?
Lazy loading defers fetching an associated object or collection until the moment it's actually accessed in application code, rather than fetching it eagerly as part of the initial query, which can avoid unnecessary work when a related object isn't always needed.
30. Explain the lifecycle of a SqlSession?
A SqlSession moves through a defined, short-lived lifecycle: created from a SqlSessionFactory, used to execute one or more statements (typically within a single logical unit of work), and then explicitly closed, with the details of commit/rollback timing depending on whether it's being managed ma...
31. What is the difference between SqlSessionFactory and SqlSessionFactoryBuilder?
These are two distinct objects in MyBatis's bootstrap process, each with a narrow, single-purpose role: the builder constructs a factory from configuration, and the factory then produces sessions on an ongoing basis. SqlSessionFactoryBuilder SqlSessionFactory A one-time-use builder that reads con...
32. How does MyBatis's first-level cache work?
The first-level cache is a session-scoped cache, enabled by default and not independently configurable off, that stores the results of queries executed within a single SqlSession — if the exact same query with the exact same parameters is executed again on that same session, MyBatis returns...
33. How does MyBatis's second-level cache work?
The second-level cache is an optional, mapper-scoped (namespace-scoped) cache that persists across sessions, storing query results so that different SqlSession instances executing the same query against the same mapper can share cached results rather than each hitting the database independently. ...
34. What is the difference between first-level and second-level cache?
Both caches avoid redundant database queries, but they differ substantially in scope, default status, and the kind of staleness risk they carry. First-Level Cache Second-Level Cache Scoped to a single SqlSession. Scoped to a mapper namespace, shared across sessions. Enabled by default, cannot be ...
35. Explain how to implement a custom TypeHandler in MyBatis?
A TypeHandler controls how MyBatis converts between a Java type and a JDBC type during parameter binding and result mapping; a custom TypeHandler is needed when a Java type doesn't have built-in support, or when the default conversion behavior isn't what a specific column requires — a commo...
36. What is the purpose of the if, choose, when, otherwise dynamic SQL elements?
These elements provide conditional branching logic within a SQL statement, mirroring familiar programming constructs —
37. Explain the internal working of the foreach element for batch operations?
The
38. How do you handle batch inserts/updates in MyBatis?
MyBatis supports batch operations two main ways: using the
39. What is the Mapper proxy pattern, and how does MyBatis use it internally?
MyBatis generates a working implementation of a Mapper interface at runtime using Java's dynamic proxy mechanism, rather than requiring a hand-written implementation class — when application code calls session.getMapper(UserMapper.class) , what's actually returned is a proxy object implemen...
40. Explain the execution flow of a MyBatis query from mapper call to result?
A single mapper method call moves through several internal MyBatis layers before returning a mapped Java result, each responsible for a distinct part of translating a typed Java call into an executed SQL statement and back. flowchart TD A[Application calls mapper.selectUserById 1] --> B[MapperPro...
41. What is the difference between MyBatis annotations and XML mapping?
Both approaches define the same underlying concept — SQL statements tied to Mapper interface methods — but they differ in where that definition lives and how well each scales to more complex mapping needs. Annotations XML Mapping SQL written directly on the interface method, e.g. @Sel...
42. How do you use MyBatis with multiple data sources?
Supporting multiple databases in a single MyBatis application generally means configuring a separate SqlSessionFactory (and corresponding DataSource) per database, with mappers explicitly associated with the correct factory rather than assuming a single, application-wide default. @Configuration @...
43. Explain the role of the Executor in MyBatis's internal architecture, including the SIMPLE, REUSE, and BATCH executor types?
The Executor is the core internal component responsible for actually carrying out a statement's execution against the database, sitting between the SqlSession's public API and the lower-level StatementHandler/ParameterHandler/ResultSetHandler pipeline, and MyBatis supports three distinct Executor...
44. How does MyBatis handle transactions, and how does it integrate with Spring's transaction management?
In plain, non-Spring MyBatis usage, transaction boundaries are managed directly through the SqlSession — an explicit commit() persists changes, an explicit rollback() discards them, and by default a session is not in auto-commit mode, meaning a developer is responsible for calling one or th...
45. What is a plugin/interceptor in MyBatis, and how do you write one?
A MyBatis plugin is a custom interceptor that hooks into one of four specific internal interfaces — Executor, ParameterHandler, ResultSetHandler, or StatementHandler — letting a developer intercept and modify behavior at a specific stage of the query execution pipeline, such as loggin...
46. Explain how pagination is typically implemented in MyBatis?
MyBatis offers a built-in but limited mechanism, RowBounds , alongside more commonly used approaches that push pagination logic directly into the SQL itself or rely on a plugin to automate it, and understanding the trade-offs between them matters for building efficient, large-scale queries. Appro...
47. What is the N+1 select problem, and how does it relate to MyBatis?
The N+1 select problem occurs when fetching a list of N parent records triggers one additional query per parent to fetch each one's related data, resulting in 1 (for the parent list) plus N (one per parent's related data) separate queries, instead of a single, more efficient query that retrieves ...
48. How do you troubleshoot a MyBatis mapping exception?
MyBatis mapping errors generally fall into a handful of recurring categories, and working through them in a consistent order — from configuration issues to type mismatches — is usually faster than guessing at the root cause from the exception message alone. Check the exception's root ...
49. Explain the internal working of MyBatis's dynamic SQL parsing?
When MyBatis loads a Mapper XML file containing dynamic SQL elements, it doesn't treat the statement as a plain string; instead, it parses the XML structure into a tree of SqlNode objects — one node type per dynamic SQL element — that gets evaluated fresh for every statement execution...
50. Explain the execution flow of MyBatis-Spring-Boot-Starter's auto-configuration?
When mybatis-spring-boot-starter is on the classpath of a Spring Boot application, its auto-configuration class activates automatically (conditioned on a DataSource bean being present) and wires up the SqlSessionFactory, mapper scanning, and related beans without requiring explicit XML or Java co...
