Mybatis return large result with xml configuration in spring

Question

I need to dump data from a table in oracle to elasticsearch(100 Million record), My memory limit of JVM is 256M, I use the following code and config to get the data from oracle

Answer 1

There are two options:

1. use ResultHandler
2. since 3.4.1 use Cursor

ResultHandler

That is how you can use custom ResultHandler:

PersonMapper.xml

  
    
    
  
  
     SELECT * FROM person
  

PersonMapper.java

public interface PersonMapper {
     void selectAllPersons(ResultHandler handler);
}

MyService.java

class PersonResultHandler implements ResultHandler {
    @Override
    public void handleResult(ResultContext context) { 
        Person person = (Person)context.getResultObject(); 
        // process person here
    }
};
PersonResultHandler handler = new PersonResultHandler();
PersonMapper personMapper = ...;
personMapper.selectAllPersons(handler);

Cursor

Starting from mybatis 3.4.1 you can return Cursor which is Iterable and can be used like this (under condition that result is ordered, see above Cursor API java doc for details):

PersonMapper.java

public interface PersonMapper {
     Cursor selectAllPersons();
}

MyService.java

PersonMapper personMapper = ...;
try (Cursor persons = personMapper.selectAllPersons()) {
   for (Person person : persons) {
      // process one person
   }
}