Java Reflection Java 

This tutorial shows different ways to set field values by using Java Reflection.

Examples

Example POJO

public class Person {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                '}';
    }
}

Using java.lang.reflect.Field

package com.logicbig.example;

import java.lang.reflect.Field;

public class JavaFieldExample {
    public static void main(String[] args) throws Exception {
        Person p = new Person();
        System.out.println("before: "+p);
        Field field = Person.class.getDeclaredField("name");
        field.setAccessible(true);
        field.set(p, "Tina");
        field.setAccessible(false);
        System.out.println("after: "+p);
    }
}

before: Person{name='null'}
after: Person{name='Tina'}

Invoking setter via java.lang.reflect.Method

package com.logicbig.example;

import java.lang.reflect.Method;

public class JavaSetterMethodExample {
    public static void main(String[] args) throws Exception {
        Person p = new Person();//must have setter
        System.out.println("before: "+p);
        Method setter = Person.class.getDeclaredMethod("setName", String.class);
        setter.invoke(p, "Tina");
        System.out.println("after: "+p);
    }
}

before: Person{name='null'}
after: Person{name='Tina'}

Using BeanInfo

package com.logicbig.example;

import java.beans.BeanInfo;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.util.Arrays;
import java.util.Optional;

public class JavaBeanInfoExample {
    public static void main(String[] args) throws Exception {
        Person p = new Person();//must have getters and setters
        System.out.println("before: " + p);
        BeanInfo beanInfo = Introspector.getBeanInfo(Person.class);
        Optional<PropertyDescriptor> propertyDescriptor = Arrays.stream(beanInfo.getPropertyDescriptors())
                                                                .filter(pd -> pd.getName().equals("name"))
                                                                .findAny();
        if (propertyDescriptor.isPresent()) {
            propertyDescriptor.get().getWriteMethod().invoke(p, "Tina");
            System.out.println("after: " + p);
        }
    }
}

before: Person{name='null'}
after: Person{name='Tina'}

Using Commons BeanUtils

pom.xml

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

package com.logicbig.example;

import org.apache.commons.beanutils.BeanUtils;

public class ApacheCommonBeanUtilsExample {
    public static void main(String[] args) throws Exception {
        Person p = new Person();//must have getters and setters
        System.out.println("before: " + p);
        BeanUtils.setProperty(p, "name", "Tina");
        System.out.println("after: " + p);
    }
}

before: Person{name='null'}
after: Person{name='Tina'}

Using Spring beans

pom.xml

<dependency>
   <groupId>org.springframework</groupId>
   <artifactId>spring-beans</artifactId>
   <version>5.2.5.RELEASE</version>
</dependency>

Direct field Access

package com.logicbig.example;

import org.springframework.beans.ConfigurablePropertyAccessor;
import org.springframework.beans.PropertyAccessorFactory;

public class SpringFieldAccessorExample {
    public static void main(String[] args) {
        Person p = new Person();
        System.out.println("before: "+p);
        ConfigurablePropertyAccessor propertyAccessor = PropertyAccessorFactory.forDirectFieldAccess(p);
        propertyAccessor.setPropertyValue("name", "Tina");
        System.out.println("after: "+p);
    }
}

before: Person{name='null'}
after: Person{name='Tina'}

Setter access

package com.logicbig.example;

import org.springframework.beans.ConfigurablePropertyAccessor;
import org.springframework.beans.PropertyAccessorFactory;

public class SpringPropertyAccessorExample {
    public static void main(String[] args) {
        Person p = new Person();//must have getters and setters
        System.out.println("before: " + p);
        ConfigurablePropertyAccessor propertyAccessor = PropertyAccessorFactory.forBeanPropertyAccess(p);
        propertyAccessor.setPropertyValue("name", "Tina");
        System.out.println("after: " + p);
    }
}

before: Person{name='null'}
after: Person{name='Tina'}

Example Project

Dependencies and Technologies Used:

• commons-beanutils 1.9.4: Apache Commons BeanUtils provides an easy-to-use but flexible wrapper around reflection and introspection.
• spring-beans 5.2.5.RELEASE: Spring Beans.
• JDK 8
• Maven 3.5.4