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1. Overview

In this quick article, we’ll use the Java 8 Stream API and the Introspector class – to invoke all getters found in a POJO.

We will create a stream of getters, inspect return values and see if a field value is null.

2. Setup

The only setup we need is to create a simple POJO class:

public class Customer {

    private Integer id;
    private String name;
    private String emailId;
    private Long phoneNumber;

    // standard getters and setters
}

3. Invoking Getter Methods

We’ll analyze the Customer class using Introspector; this provides an easy way for discovering properties, events, and methods supported by a target class.

We’ll first collect all the PropertyDescriptor instances of our Customer class. PropertyDescriptor captures all the info of a Java Bean property:

PropertyDescriptor[] propDescArr = Introspector
  .getBeanInfo(Customer.class, Object.class)
  .getPropertyDescriptors();

Let’s now go over all PropertyDescriptor instances, and invoke the read method for every property:

return Arrays.stream(propDescArr)
  .filter(nulls(customer))
  .map(PropertyDescriptor::getName)
  .collect(Collectors.toList());

The nulls predicate we use above checks if the property can be read invokes the getter and filters only null values:

private static Predicate<PropertyDescriptor> nulls(Customer customer) { 
    return = pd -> { 
        Method getterMethod = pd.getReadMethod(); 
        boolean result = false; 
        return (getterMethod != null && getterMethod.invoke(customer) == null); 
    }; 
}

Finally, let’s now create an instance of a Customer, set a few properties to null and test our implementation:

@Test
public void givenCustomer_whenAFieldIsNull_thenFieldNameInResult() {
    Customer customer = new Customer(1, "John", null, null);
	    
    List<String> result = Utils.getNullPropertiesList(customer);
    List<String> expectedFieldNames = Arrays
      .asList("emailId","phoneNumber");
	    
    assertTrue(result.size() == expectedFieldNames.size());
    assertTrue(result.containsAll(expectedFieldNames));      
}

4. Conclusion

In this short tutorial, we made good use of the Java 8 Stream API and an Introspector instance – to invoke all getters and retrieve a list of null properties.

As usual, the code is available over on GitHub.

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