How to Replace Any Bean Method in Spring 6 Using MethodReplacer

Environment: Spring 6.1.2

1. Introduction

Method replacement allows you to replace any method of a managed bean with your own implementation. Instead of modifying source code, Spring provides a mechanism to intercept the original method and execute custom logic.

2. Practical Example

2.1 Prepare Code

@Component
public class PersonService {
  public String savePerson(Person person) {
    return "save person";
  }
}

The savePerson method will be replaced.

2.2 Replacement Implementation

public class ReplacementSavePerson implements MethodReplacer {
  @Override
  public Object reimplement(Object obj, Method method, Object[] args) throws Throwable {
    System.out.println(Arrays.toString(args));
    System.out.println(obj);
    return "replace save person";
  }
}

This class implements org.springframework.beans.factory.support.MethodReplacer and provides the new method body.

2.3 Register Beans and Define Override

public static void main(String[] args) {
  try (GenericApplicationContext context = new GenericApplicationContext()) {
    context.registerBean("replacementSavePerson", ReplacementSavePerson.class);
    context.registerBean(PersonService.class, bd -> {
      if (bd instanceof RootBeanDefinition root) {
        // specify method to replace
        ReplaceOverride replace = new ReplaceOverride("savePerson", "replacementSavePerson");
        root.getMethodOverrides().addOverride(replace);
      }
    });
    context.refresh();
    PersonService ps = context.getBean(PersonService.class);
    System.out.println(ps.savePerson(new Person()));
  }
}

Running the program prints the bean information and the string replace save person, showing that the original method has been replaced by ReplacementSavePerson.reimplement.

2.4 Overloaded Methods

If the target class contains overloaded methods, you can add type identifiers to the ReplaceOverride to select the correct method, e.g.:

ReplaceOverride replace = new ReplaceOverride("savePerson", "replacementSavePerson");
replace.addTypeIdentifier("com.pack.Person"); // or "Person", "P", "er"

2.5 XML Configuration

<bean id="personService" class="com.pack.PersonService">
  <replaced-method name="savePerson" replacer="replacementComputeValue">
    <arg-type>Person</arg-type>
  </replaced-method>
</bean>

<bean id="replacementSavePerson" class="com.pack.ReplacementSavePerson"/>

XML configuration is straightforward, while annotation‑based replacement requires manual ReplaceOverride registration.

End of article.