BAEL-869 - Java 8 example of listing null properties

core-java/src/main/java/com/baeldung/reflection/BaeldungReflectionUtils.java

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+package com.baeldung.reflection;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.beans.Introspector;
+import java.beans.PropertyDescriptor;
+import java.lang.reflect.Method;
+import java.util.Arrays;
+import java.util.List;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class BaeldungReflectionUtils {
+
+    private static final Logger LOG = LoggerFactory.getLogger(BaeldungReflectionUtils.class);
+
+
+    public static List<String> getNullPropertiesList(Customer customer) throws Exception {
+        PropertyDescriptor[] propDescArr = Introspector.getBeanInfo(Customer.class, Object.class).getPropertyDescriptors();
+        List<PropertyDescriptor> propDescList = Arrays.asList(propDescArr);
+
+        List<String> nullProps = propDescList.stream()
+                .filter(nulls(customer))
+                .map(PropertyDescriptor::getName)
+                .collect(Collectors.toList());
+        return nullProps;
+    }
+
+    private static Predicate<PropertyDescriptor> nulls(Customer customer) {
+        Predicate<PropertyDescriptor> isNull = pd -> {
+            Method getterMethod = pd.getReadMethod();
+            boolean result = false;
+            try {
+                result = (getterMethod != null && getterMethod.invoke(customer) == null);
+            } catch (Exception e) {
+                LOG.error("error invoking getter method");
+            }
+            return result;
+        };
+        return isNull;
+    }
+}

core-java/src/main/java/com/baeldung/reflection/Customer.java

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+package com.baeldung.reflection;
+
+public class Customer {
+
+    private Integer id;
+    private String name;
+    private String emailId;
+    private Long phoneNumber;
+
+    public Integer getId() {
+        return id;
+    }
+
+    public void setId(Integer id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getEmailId() {
+        return emailId;
+    }
+
+    public void setEmailId(String emailId) {
+        this.emailId = emailId;
+    }
+
+    @Override
+    public String toString() {
+        StringBuilder builder = new StringBuilder();
+        builder.append("Customer [id=").append(id).append(", name=").append(name).append(", emailId=").append(emailId).append(", phoneNumber=")
+                .append(phoneNumber).append("]");
+        return builder.toString();
+    }
+
+    public Customer(Integer id, String name, String emailId, Long phoneNumber) {
+        super();
+        this.id = id;
+        this.name = name;
+        this.emailId = emailId;
+        this.phoneNumber = phoneNumber;
+    }
+
+    public Long getPhoneNumber() {
+        return phoneNumber;
+    }
+
+    public void setPhoneNumber(Long phoneNumber) {
+        this.phoneNumber = phoneNumber;
+    }
+
+}

core-java/src/test/java/com/baeldung/reflection/BaeldungReflectionUtilsTest.java

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+package com.baeldung.reflection;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+public class BaeldungReflectionUtilsTest {
+
+    @Test
+    public void givenCustomer_whenAFieldIsNull_thenFieldNameInResult() throws Exception {
+        Customer customer = new Customer(1, "Himanshu", null, null);
+
+        List<String> result = BaeldungReflectionUtils.getNullPropertiesList(customer);
+        List<String> expectedFieldNames = Arrays.asList("emailId", "phoneNumber");
+
+        Assert.assertTrue(result.size() == expectedFieldNames.size());
+        Assert.assertTrue(result.containsAll(expectedFieldNames));
+
+    }
+
+}