How To Use Reflection To Copy Properties From Pojo To Other Java Beans

Copying properties from one object to another using reflection

Copying properties from one object to another using reflection in Java can be achieved by leveraging the java.lang.reflect package. This is particularly useful when you want to copy properties between objects without knowing their types at compile time, as is often the case in frameworks or utility libraries.

Here’s a step-by-step guide on how to implement this:

Step-by-Step Guide

1. Create the Source and Target Classes: Define the classes from which you will copy properties.
2. Use Reflection to Access Fields: Use reflection to access and copy the fields from one object to another.

Example

Here is an example of copying properties from one object to another using reflection:

Source Class

java

public class Source {     private String name;     private int age;         public Source() {}       public Source(String name, int age) {         this.name = name;         this.age = age;     }       // Getters and Setters     public String getName() {         return name;     }       public void setName(String name) {         this.name = name;     }       public int getAge() {         return age;     }       public void setAge(int age) {         this.age = age;     } }

 

Target Class

java

public class Target {     private String name;     private int age;         public Target() {}       // Getters and Setters     public String getName() {         return name;     }       public void setName(String name) {         this.name = name;     }       public int getAge() {         return age;     }       public void setAge(int age) {         this.age = age;     } }

 

Reflection Utility Class

java

import java.lang.reflect.Field;   public class ReflectionUtils {       public static void copyProperties(Object source, Object target) {         if (source == null || target == null) {             throw new IllegalArgumentException("Source and target must not be null");         }           Class<?> sourceClass = source.getClass();         Class<?> targetClass = target.getClass();           Field[] sourceFields = sourceClass.getDeclaredFields();         for (Field sourceField : sourceFields) {             try {                 Field targetField = targetClass.getDeclaredField(sourceField.getName());                 if (targetField.getType().equals(sourceField.getType())) {                     sourceField.setAccessible(true);                     targetField.setAccessible(true);                     targetField.set(target, sourceField.get(source));                 }             } catch (NoSuchFieldException | IllegalAccessException e) {                 // Field not found in target or cannot access field, ignore and continue                 continue;             }         }     }       public static void main(String[] args) {         Source source = new Source("John Doe", 30);         Target target = new Target();           copyProperties(source, target);           System.out.println("Target name: " + target.getName());         System.out.println("Target age: " + target.getAge());     } }

 

Explanation

1. Field Access: The copyProperties method iterates over all fields in the source object.
2. Field Matching: For each field in the source object, it looks for a corresponding field in the target object with the same name and type.
3. Field Copying: If a matching field is found, the method makes the fields accessible (even if they are private) and copies the value from the source field to the target field.

Handling Exceptions

• NoSuchFieldException: This exception is thrown if a field in the source object does not exist in the target object. In this example, we simply continue to the next field.
• IllegalAccessException: This exception is thrown if the field cannot be accessed. The example handles this by setting the field to be accessible.

Considerations

• Performance: Using reflection can be slower compared to direct field access due to the overhead of reflective operations.
• Security: Accessing private fields with reflection can violate encapsulation principles. Ensure this approach aligns with your security policies.
• Inheritance: The current implementation does not handle inherited fields. You might need to recursively inspect superclasses if your objects have inheritance hierarchies.

This example provides a basic implementation of copying properties using reflection in Java. You can further enhance this utility to handle more complex scenarios, such as deep copying nested objects or handling collections.

 

Copying properties from one object to another using third party jar

Apache Commons BeanUtils provides a utility to copy properties from one bean to another using reflection, making it simpler and more robust compared to manually using reflection. The BeanUtils.copyProperties method can be used for this purpose.

Maven Dependency

First, you need to add the Apache Commons BeanUtils dependency to your Maven pom.xml file:

xml

<dependency>     <groupId>commons-beanutils</groupId>     <artifactId>commons-beanutils</artifactId>     <version>1.9.4</version> </dependency>

 

Example

Here’s a step-by-step example demonstrating how to use BeanUtils.copyProperties to copy properties from one object to another.

Source Class

java

public class Source {     private String name;     private int age;         public Source() {}       public Source(String name, int age) {         this.name = name;         this.age = age;     }       // Getters and Setters     public String getName() {         return name;     }       public void setName(String name) {         this.name = name;     }       public int getAge() {         return age;     }       public void setAge(int age) {         this.age = age;     } }

 

Target Class

java

public class Target {     private String name;     private int age;         public Target() {}       // Getters and Setters     public String getName() {         return name;     }       public void setName(String name) {         this.name = name;     }       public int getAge() {         return age;     }       public void setAge(int age) {         this.age = age;     } }

 

Utility Class to Copy Properties

Java

import org.apache.commons.beanutils.BeanUtils;   public class BeanUtilsExample {       public static void copyProperties(Object source, Object target) {         try {             BeanUtils.copyProperties(target, source);         } catch (Exception e) {             e.printStackTrace();             // Handle exceptions appropriately         }     }       public static void main(String[] args) {         Source source = new Source("John Doe", 30);         Target target = new Target();           copyProperties(source, target);           System.out.println("Target name: " + target.getName());         System.out.println("Target age: " + target.getAge());     } }

 

Explanation

1. Dependencies: Ensure you have the Apache Commons BeanUtils dependency added to your project.
2. Source and Target Classes: These classes are simple Java beans with private fields and public getters and setters.
3. Copy Properties: The copyProperties method in the BeanUtilsExample class uses BeanUtils.copyProperties to copy properties from the source object to the target object.
4. Error Handling: The method catches and prints exceptions. In a real-world application, you might want to handle exceptions more gracefully.

Considerations

• Nested Properties: BeanUtils.copyProperties only performs a shallow copy. If your objects contain nested objects, only references will be copied.
• Performance: Using reflection can be slower than direct field access. For large objects or performance-critical applications, consider other