How to correctly use @ResultType annotation in MyBatis?
Apr 19, 2025 pm 05:39 PM
Correct use of @ResultType annotation in MyBatis
This article discusses the usage of @ResultType annotation in MyBatis and clarifies its relationship with ResultHandler . Source code analysis shows that the @ResultType annotation only takes effect when the method return type is void .
Misconceptions and clarifications:
Many developers mistakenly believe that @ResultType directly specifies the return value type. In fact, when the method returns void , @ResultType tells MyBatis how to map the query result to the specified type ( Student.class ), which is usually used with ResultHandler . If the method returns a non- void type, @ResultType will be ignored and MyBatis will map according to the method return type.
Correct usage method:
The following example shows the correct combination of @ResultType and ResultHandler :
@Select("select * from student")
@ResultType(Student.class)
void queryStudent(StudentResultHandler resultHandler);
public class StudentResultHandler implements ResultHandler<student> {
private final List<student> students = new ArrayList();
@Override
public void handleResult(ResultContext extends Student> context) {
Student student = context.getResultObject();
students.add(student);
}
public List<student> getStudents() {
return students;
}
}</student></student></student>
In this example:
-
queryStudentmethod returnsvoid. -
@ResultType(Student.class)Tell MyBatis to map the query results toStudentobjects. -
StudentResultHandlerimplements theResultHandlerinterface, processes query results row by row, and adds eachStudentobject to thestudentslist. - The caller needs to get the result list through
resultHandler.getStudents().
Other situations:
@ResultMapannotation: If the XML mapping file is used<resultmap></resultmap>Defining the result map, you should use the@ResultMapannotation instead of@ResultType.Non-
voidreturn type: if method returnsList<student></student>orStudent, without@ResultType, MyBatis will automatically map according to the return type.
Summarize:
@ResultType annotation is mainly used for void return type methods, and it implements custom result processing logic in conjunction with ResultHandler . For non- void return types, MyBatis will automatically map based on the return type without @ResultType . Selecting @ResultType or @ResultMap depends on whether XML result mapping is used. Only by understanding these differences can you use MyBatis annotations correctly and effectively.
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