In the post reflection in java – method it is already explained how you can invoke a method of the class at runtime. In this post we’ll use that knowledge to invoke getters and setters of the class using Java reflection API. In Java you can do it using two ways.
In this post we'll see example of both of these ways to invoke getters and setters of the class.
Using PropertyDescriptor class
A PropertyDescriptor describes one property that a Java Bean exports via a pair of accessor methods. Then using the getReadMethod() and getWriteMethod() you can call the setter and getter for the property.
Invoking getters and setters using PropertyDescriptor example
Here in the example we have a class TestClass which has getter and setter for three fields which are of type int, String and boolean. Then in the GetterAndSetter class there are methods to invoke the getters and setters of the given class.
TestClass.java
package org.prgm;
public class TestClass {
private int value;
private String name;
private boolean flag;
public int getValue() {
return value;
}
public void setValue(int value) {
this.value = value;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public boolean isFlag() {
return flag;
}
public void setFlag(boolean flag) {
this.flag = flag;
}
}
GetterAndSetter.java
import java.beans.IntrospectionException;
import java.beans.PropertyDescriptor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
public class GetterAndSetter {
public static void main(String[] args) {
GetterAndSetter gs = new GetterAndSetter();
TestClass tc = new TestClass();
gs.callSetter(tc, "name", "John");
gs.callSetter(tc, "value", 12);
gs.callSetter(tc, "flag", true);
// Getting fields of the class
Field[] fields = tc.getClass().getDeclaredFields();
for(Field f : fields){
String fieldName = f.getName();
System.out.println("Field Name -- " + fieldName);
}
gs.callGetter(tc, "name");
gs.callGetter(tc, "value");
gs.callGetter(tc, "flag");
}
private void callSetter(Object obj, String fieldName, Object value){
PropertyDescriptor pd;
try {
pd = new PropertyDescriptor(fieldName, obj.getClass());
pd.getWriteMethod().invoke(obj, value);
} catch (IntrospectionException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private void callGetter(Object obj, String fieldName){
PropertyDescriptor pd;
try {
pd = new PropertyDescriptor(fieldName, obj.getClass());
System.out.println("" + pd.getReadMethod().invoke(obj));
} catch (IntrospectionException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
Output
Field Name -- value Field Name -- name Field Name -- flag John 12 true
Scanning methods of the class and look for set and get methods
Another way to invoke the getters and setters using Java reflection is to scan all the methods of the class through reflection and then find out which are the getters and setters method.
It is particularly useful to use this way to call get methods if you have lots of fields in a class. Calling set method that way won’t be of much help as you will have to still invoke individual method with the value that has to be set.
Logic to identify get method
get method starts with get or is (in case of boolean), it should not have any parameters and it should return a value.
Logic to identify set method
set method starts with set and it should have a parameter and it shouldn't return any value which means it should return void.
In the example same Java bean class as above TestClass is used.
In the GetterAndSetter class there are methods to identify the getters and setters of the given class. If it is a get method that is invoked to get the value. For set method invocation is done to set the property values.
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class GetterAndSetter {
public static void main(String[] args) {
TestClass tc = new TestClass();
// get all the methods of the class
Method[] methods = tc.getClass().getDeclaredMethods();
// Initially calling all the set methods to set values
for(Method method : methods){
if(isSetter(method)){
System.out.println("Setter -- " + method.getName());
try {
if(method.getName().contains("Name")) {
method.invoke(tc, "John");
}
if(method.getName().contains("Value")) {
method.invoke(tc, 12);
}
if(method.getName().contains("Flag")) {
method.invoke(tc, true);
}
} catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
// calling getters
for(Method method : methods){
if(isGetter(method)){
try {
Object obj = method.invoke(tc);
System.out.println("Invoking "+ method.getName() + " Returned Value - " + obj);
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IllegalArgumentException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (InvocationTargetException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
private static boolean isGetter(Method method){
// identify get methods
if((method.getName().startsWith("get") || method.getName().startsWith("is"))
&& method.getParameterCount() == 0 && !method.getReturnType().equals(void.class)){
return true;
}
return false;
}
private static boolean isSetter(Method method){
// identify set methods
if(method.getName().startsWith("set") && method.getParameterCount() == 1
&& method.getReturnType().equals(void.class)){
return true;
}
return false;
}
}
Output
Setter -- setName Setter -- setValue Setter -- setFlag Invoking getName Returned Value - John Invoking getValue Returned Value - 12 Invoking isFlag Returned Value - true
That's all for this topic Invoking Getters And Setters Using Reflection in Java. If you have any doubt or any suggestions to make please drop a comment. Thanks!
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