I try to copy an object by reflection. I haven't difficulties with copy primitive types, but i dont understand how copy reference types.
import java.lang.reflect.Field;
import java.util.HashSet;
import java.util.Set;
public class ReflMethod {
private static final Set<Class<?>> WRAPPER_TYPES = getWrapperTypes();
public Object CopyObject(Object object) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
Class clazz = object.getClass();
Field[] fields = clazz.getDeclaredFields();
Object instance = object.getClass().newInstance();
for(Field field : fields) {
field.setAccessible(true);
Class newClass = Class.forName(field.get(object).getClass().getName());
if(isWrapperType(newClass)) {
field.set(instance, field.get(object));
}
else if(!isWrapperType(newClass)) {
//WEIRDNESS HERE
field.set(instance, CopyObject(field.get(object).getClass().getName()));
//WEIRDNESS HERE
}
}
return instance;
}
public static boolean isWrapperType(Class<?> clazz)
{
return WRAPPER_TYPES.contains(clazz);
}
public static Set<Class<?>> getWrapperTypes()
{
Set<Class<?>> ret = new HashSet<Class<?>>();
ret.add(Boolean.class);
ret.add(Character.class);
ret.add(Byte.class);
ret.add(Short.class);
ret.add(Integer.class);
ret.add(Long.class);
ret.add(Float.class);
ret.add(Double.class);
ret.add(Void.class);
return ret;
}
}
I want using recursion for copying reference types...Where do I think wrong?
public class Cat {
private Phone phone;
private int age;
public Cat() {
}
public Cat(int age, Phone phone) {
this.age = age;
this.phone = phone;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public Phone getPhone() {
return phone;
}
public void setPhone(Phone phone) {
this.phone = phone;
}
}
public class Phone {
private String name;
public Phone() {
}
public Phone(String name) {
this.name = name;
}
public void SetName(String name) {
this.name = name;
}
public String GetName() {
return name;
}
}
And main class:
public class MainClass {
public static void main(String[] args) throws InstantiationException, IllegalAccessException, ClassNotFoundException, NoSuchMethodException {
ReflMethod reflMethod = new ReflMethod();
Phone phone1 = new Phone("IPhone");
Cat cat1 = new Cat(20, phone1);
Cat cat2 = (Cat)reflMethod.CopyObject(cat1);
System.out.println("cat1 : " + cat1.getAge() + " " + cat1.getPhone().GetName());
System.out.println("cat2 : " + cat2.getAge() + " " + cat2.getPhone().GetName());
cat1.setAge(100);
Phone phone = new Phone("Af");
cat1.setPhone(phone);
System.out.println("cat1 : " + cat1.getAge() + " " + cat1.getPhone().GetName());
System.out.println("cat2 : " + cat2.getAge() + " " + cat2.getPhone().GetName());
}
}
The code doesn't work because of the code marked as WEIRDNESS HERE.
The answer was found in the depths of Stackoverflow :D
But it doesn't work with collections :(
ReflMethod:
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
public class ReflMethod {
public static Object CopyObject(Object object)
{
try
{
Object clone = object.getClass().newInstance();
for(Field field : object.getClass().getDeclaredFields()) {
field.setAccessible(true);
if(field.get(object) == null || Modifier.isFinal(field.getModifiers()))
{
continue;
}
if(field.getType().isPrimitive()
|| field.getType().equals(String.class)
|| field.getType().getSuperclass().equals(Number.class)
|| field.getType().equals(Boolean.class))
{
field.set(clone, field.get(object));
}
else {
Object childObj = field.get(object);
if(childObj == object) {
field.set(clone,clone);
}
else {
field.set(clone,CopyObject(field.get(object)));
}
}
}
return clone;
}
catch (Exception e) {
return null;
}
}
}
Related
I have a base class
public class Box<T> {
private T entity;
public T getEntity() {
return entity;
}
void setEntity(T entity) {
this.entity = entity;
}
}
It has 2 implementations.
// Class Person
public class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
}
// Class Machine
public class Machine {
private String macAddress;
private String type;
public Machine(String macAddress, String type) {
this.macAddress = macAddress;
this.type = type;
}
}
If I want to serialise either of classA or class B objects, I will do it like this
Type typeTokenPerson = new TypeToken< Box <Person>>() {}.getType();
String userJson = gson.toJson(boxWithPersonObject, typeTokenPerson);
But the problem here is I need to know the type at compile time. I have a use case where I don't know this at compile-time, in other words, I have a json which I want to deserialize into either Person or Animal and I want to do this at runtime based on some condition.
Is there a way to do this usig Gson ?
Example:
Lets say we have a json like this
{
"entity": {
"name": "ABC",
"age": 10
}
}
This is of type Person. I want to deserialise this into an object of type Box<Person>
Gson can do it like this.
package com.example.demo;
import com.google.common.reflect.TypeToken;
import com.google.gson.Gson;
import org.junit.jupiter.api.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.lang.reflect.Type;
import java.time.Duration;
import java.time.LocalDateTime;
public class GsonDemo {
private Logger logger = LoggerFactory.getLogger(this.getClass());
private <T> Box<T> parseResponse(String responseData) {
Gson gson = new Gson();
Type jsonType = new TypeToken<Box<T>>() {
}.getType();
Box<T> result = gson.fromJson(responseData, jsonType);
return result;
}
#Test
public void test() {
LocalDateTime start = LocalDateTime.now();
try {
String json = "{ \"entity\": { \"name\": \"ABC\", \"age\": 10 }}";
Box<Person> objectBox = parseResponse(json);
System.out.println(objectBox);
String json2 = "{\n \"entity\": { \"macAddress\": \"DEF\", \"type\": \"def\" }}";
Box<Machine> objectBox2 = parseResponse(json2);
System.out.println(objectBox2);
} catch (Exception e) {
logger.error("Error", e);
}
LocalDateTime end = LocalDateTime.now();
logger.info("Cost time {}", Duration.between(start, end).toMillis() + "ms");
}
public class Box<T> {
private T entity;
public T getEntity() {
return entity;
}
void setEntity(T entity) {
this.entity = entity;
}
#Override
public String toString() {
return "Box{" + "entity=" + entity + '}';
}
}
public class Person {
private String name;
private Integer age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
#Override
public String toString() {
return "Person{" + "name='" + name + '\'' + ", age=" + age + '}';
}
}
public class Machine {
private String macAddress;
private String type;
public Machine(String macAddress, String type) {
this.macAddress = macAddress;
this.type = type;
}
public String getMacAddress() {
return macAddress;
}
public void setMacAddress(String macAddress) {
this.macAddress = macAddress;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
#Override
public String toString() {
return "Machine{" + "macAddress='" + macAddress + '\'' + ", type='" + type + '\'' + '}';
}
}
}
This elementary program is driving me up the wall.
There must be something very simple I don't see here.
WHY is the exception triggered?
There are 2 classes:
1)
public class Person
{
private String name;
private int age;
private static int numberOfPeople = 0;
public Person()
{
this("John Doe", 0);
numberOfPeople++;
}
public Person(String name, int age)
{
this.setAge(age);
this.setName(name);
numberOfPeople++;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public void setName(String name) {
this.name = name;
}
public void setAge(int age) {
this.age = age;
}
public int getNumberOfPersons()
{
return numberOfPeople;
}
public String toString()
{
return this.name + " " + this.age;
}
}
2)
import java.util.Random;
public class Adult extends Person
{
private String number;
public static final int MIN_AGE = 18;
public Adult(String name, int age, String number)
{
super(name, 0);
this.setAge(age);
this.number = number;
}
public Adult(Adult adult)
{
this(adult.getName(), adult.getAge(), adult.getNumber());
}
public Adult()
{
this.number = "";
this.setAge(MIN_AGE);
Random rand = new Random();
int result = rand.nextInt(2);
if (result == 0)
{
this.setName("John Doe");
}
else
{
this.setName("Jane Doe");
}
}
public void setAge(int age)
{
if (age < MIN_AGE)
{
throw new IllegalArgumentException("The person must be 18 or older!");
}
else
{
super.setAge(MIN_AGE);
}
}
public String getNumber()
{
return this.number;
}
private void setNumber(String number)
{
this.number = number;
}
public String toString()
{
return this.getName() + " " + this.getNumber() + " " + this.getAge();
}
public boolean equals(Object obj)
{
boolean result = false;
if (obj != null && this.getClass() == obj.getClass())
{
Adult other = (Adult) obj;
if (this.getName().equals(other.getName()) &&
this.getNumber().equals(other.getNumber()) &&
this.getAge() == other.getAge())
{
result = true;
}
}
return result;
}
public static void main(String[] args)
{
Adult ad = new Adult();
System.out.println(ad);
}
}
This gives my the following error:
Exception in thread "main" java.lang.IllegalArgumentException: The person must be 18 or older!
at people.Adult.setAge(Adult.java:39)
at people.Person.<init>(Person.java:16)
at people.Adult.<init>(Adult.java:12)
at people.Adult.main(Adult.java:75)
Your Person() constructor creates another person. Since Adult extends Person, there is an implicit super() call which is likely the cause of your error.
I want to serialize a object hierarchy including a list of objects which derive from the base class 'Thing'. This works fine, including deserialization - but XML-Simple insists in writing an attribute which specifies the actual used Java-class
when I create a xml file with the java code below, the content is like this:
<example1>
<things>
<fruit class="com.mumpitz.simplexmltest.Apple" id="17">
<sugar>212</sugar>
</fruit>
<fruit class="com.mumpitz.simplexmltest.Orange" id="25" weight="11.2"/>
</things>
</example1>
but this is not what I want.
I'd like to have
<example1>
<things>
<apple id="17">
<sugar>212</sugar>
</apple>
<orange id="25" weight="11.2"/>
</things>
</example1>
'apple' and 'orange' elements without a class attribute, not 'fruit' with such an attribute. Is this possible?
(The second xml complies to a existing schema; adding extra attributes is not an option)
Here's the code:
package com.mumpitz.simplexmltest;
import java.io.File;
import java.util.ArrayList;
import org.simpleframework.xml.Attribute;
import org.simpleframework.xml.Element;
import org.simpleframework.xml.ElementList;
import org.simpleframework.xml.Root;
import org.simpleframework.xml.Serializer;
import org.simpleframework.xml.core.Persister;
class Fruit {
#Attribute(name = "id")
protected final int id;
Fruit(
#Attribute(name = "id")
int id) {
this.id = id;
}
int getObjectId() {
return id;
}
}
#Root
class Apple extends Fruit {
private final int sugar;
#Element(type = Fruit.class)
public Apple(
#Attribute(name = "id")
int id,
#Element(name = "sugar")
int sugar) {
super(id);
this.sugar = sugar;
}
#Element(name = "sugar")
public int getSugar() {
return this.sugar;
}
#Override
public String toString() {
return "id: " + id + ", sugar: " + sugar;
}
}
#Root
class Orange extends Fruit {
#Attribute
public double weight;
public Orange(
#Attribute(name = "id")
int id) {
super(id);
}
#Override
public String toString() {
return "id: " + id + ", weight: " + weight;
}
}
#Root
public class Example1 {
#ElementList
public ArrayList<Fruit> things = new ArrayList<Fruit>();
#Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("things:\n");
for (int i=0; i<things.size(); i++) {
sb.append(" " + things.get(i).toString() + "\n");
}
return sb.toString();
}
//////////////////////////////////
static Example1 createDummy() {
Example1 d = new Example1();
d.things.add(new Apple(17, 212));
Orange or = new Orange(25);
or.weight = 11.2;
d.things.add(or);
return d;
}
static String msg;
static Example1 res;
static public String getMessage() {
String m = msg;
msg = null;
return m;
}
static public boolean write(String path) {
Serializer serializer = new Persister();
Example1 example = Example1.createDummy();
File result = new File(path);
try {
serializer.write(example, result);
} catch (Exception e) {
e.printStackTrace();
msg = e.getMessage();
return false;
}
return true;
}
static public boolean read(String path) {
Serializer serializer = new Persister();
File source = new File(path);
try {
res = serializer.read(Example1.class, source);
} catch (Exception e) {
e.printStackTrace();
msg = e.getMessage();
return false;
}
return true;
}
public static Object getResult() {
return res;
}
}
some hours later I found the solution. You simply have to
Read the manual
Use the #ElementListUnion annotation
package com.mumpitz.simplexmltest;
import java.io.File;
import java.util.ArrayList;
import java.util.List;
import org.simpleframework.xml.Attribute;
import org.simpleframework.xml.Element;
import org.simpleframework.xml.ElementList;
import org.simpleframework.xml.ElementListUnion;
import org.simpleframework.xml.Root;
import org.simpleframework.xml.Serializer;
import org.simpleframework.xml.core.Persister;
// the base class
#Element
class Thing {
static int count=0;
Thing() {
this.id = ++count;
}
#Attribute
protected int id;
public int getId() {
return id;
}
}
// first derived class
#Element
class Car extends Thing {
#Attribute
private String name;
Car(#Attribute(name="name") String name) {
this.name = name;
}
public String getName() {
return name;
}
#Override
public String toString() {
return "ID: " + id + " Car: " + name;
}
}
// second derived class
#Element
class House extends Thing {
#Attribute
private int price;
House(#Attribute(name="price") int price) {
this.price = price;
}
public int getPrice() {
return this.price;
}
#Override
public String toString() {
return "ID: " + id + " House: " + price;
}
}
// a class with a list of base class instances
#Root(name="ListOfThings")
public class Example4 {
// specify the derived classes used in the list
#ElementListUnion({
#ElementList(entry="house", inline=true, type=House.class),
#ElementList(entry="car", inline=true, type=Car.class)
})
private ArrayList<Thing> list = new ArrayList<Thing>();
public void add(Thing t) {
list.add(t);
}
public List<Thing> getProperties() {
return list;
}
#Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("Example4 contains " + list.size() + " elements:\n");
for (Thing t : list) {
sb.append(" " + t.toString() + "\n");
}
return sb.toString();
}
//////////////////////////////////
// test code
//////////////////////////////////
static String msg;
static Example4 res;
static public String getMessage() {
String m = msg;
msg = null;
return m;
}
static private Example4 createDummy() {
Example4 d = new Example4();
d.add(new Car("Mercedes"));
d.add(new House(34000000));
d.add(new Car("VW"));
d.add(new House(230000));
return d;
}
//////////////////////////////////
// serialize / deserialize
//////////////////////////////////
static public boolean write(String path) {
Serializer serializer = new Persister();
File result = new File(path);
Example4 example = Example4.createDummy();
try {
serializer.write(example, result);
} catch (Exception e) {
e.printStackTrace();
msg = e.getMessage();
return false;
}
return true;
}
static public boolean read(String path) {
Serializer serializer = new Persister();
File source = new File(path);
try {
res = serializer.read(Example4.class, source);
} catch (Exception e) {
e.printStackTrace();
msg = e.getMessage();
return false;
}
return true;
}
public static Object getResult() {
return res;
}
}
I getting class by name and i need to update them with respective data and my question is how to do it with java
I want to add the method some dummy data .
I don't know the class type I just getting the class name and use reflection to get his data
I use this code to get the class instance and
Class<?> classHandle = Class.forName(className);
Object myObject = classHandle.newInstance();
// iterate through all the methods declared by the class
for (Method method : classHandle.getMethods()) {
// find all the set methods
if (method.getName().matches("set[A-Z].*")
And know that I find the list of the set method I want to update it with data
how can I do that .
assume that In class name I got person and the class have setSalary and setFirstName etc
how can I set them with reflection ?
public class Person {
public void setSalery(double salery) {
this.salery = salery;
}
public void setFirstName(String FirstName) {
this.FirstName = FirstName;
}
}
Instead of trying to call a setter, you could also just directly set the value to the property using reflection. For example:
public static boolean set(Object object, String fieldName, Object fieldValue) {
Class<?> clazz = object.getClass();
while (clazz != null) {
try {
Field field = clazz.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, fieldValue);
return true;
} catch (NoSuchFieldException e) {
clazz = clazz.getSuperclass();
} catch (Exception e) {
throw new IllegalStateException(e);
}
}
return false;
}
Call:
Class<?> clazz = Class.forName(className);
Object instance = clazz.newInstance();
set(instance, "salary", 15);
set(instance, "firstname", "John");
FYI, here is the equivalent generic getter:
#SuppressWarnings("unchecked")
public static <V> V get(Object object, String fieldName) {
Class<?> clazz = object.getClass();
while (clazz != null) {
try {
Field field = clazz.getDeclaredField(fieldName);
field.setAccessible(true);
return (V) field.get(object);
} catch (NoSuchFieldException e) {
clazz = clazz.getSuperclass();
} catch (Exception e) {
throw new IllegalStateException(e);
}
}
return null;
}
Call:
Class<?> clazz = Class.forName(className);
Object instance = clazz.newInstance();
int salary = get(instance, "salary");
String firstname = get(instance, "firstname");
To update the first name
First find the field you want to update
Then find the mutator (which accepts an argument of the field's type)
Finally execute the mutator on the object with the new value:
Field field=classHandle.getDeclaredField("firstName");
Method setter=classHandle.getMethod("setFirstName", field.getType());
setter.invoke(myObject, "new value for first name");
if (method.getName().matches("set[A-Z].*") {
method.invoke(person,salary)
// and so on
}
to know the parameters you can issue method.getPagetParameterTypes()
based on the result construct your parameters and supply.
package apple;
import java.lang.reflect.Field;
import java.lang.reflect.Type;
import java.util.Map.Entry;
import java.util.Set;
import com.google.gson.Gson;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonSyntaxException;
/*
* Employe Details class
*/
class Employee {
private long id;
private String name;
private String userName;
private Address address;
private Contact contact;
private double salary;
public long getId() {
return id;
}
public void setId(long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
public Contact getContact() {
return contact;
}
public void setContact(Contact contact) {
this.contact = contact;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
}
/*
* Address class for employee
*/
class Address {
private String city;
private String state;
private String country;
private int pincode;
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
public int getPincode() {
return pincode;
}
public void setPincode(int pincode) {
this.pincode = pincode;
}
}
/*
* Contact class for Employee
*/
class Contact {
private String email;
private String contactNo;
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getContactNo() {
return contactNo;
}
public void setContactNo(String contactNo) {
this.contactNo = contactNo;
}
}
public class Server {
public static void main(String args[]) throws JsonSyntaxException, Exception{
Gson gson = new Gson();
/*
* Old Employee Data
*/
Address address = new Address();
Contact contact = new Contact();
Employee employee = new Employee();
address.setCity("shohna-road");
address.setCountry("INDIA");
address.setPincode(12201);
address.setState("Hariyana");
contact.setContactNo("+918010327919");
contact.setEmail("shivritesh9984#gmail.com");
employee.setAddress(address);
employee.setContact(contact);
employee.setId(4389573);
employee.setName("RITESH SINGH");
employee.setSalary(43578349.345);
employee.setUserName("ritesh9984");
System.out.println("Employee : "+gson.toJson(employee));
/* New employee data */
Employee emp = employee;
address.setCity("OMAX");
emp.setAddress(address);
emp.setName("RAVAN");
/* Update employee with new employee Object*/
update(employee, gson.fromJson(gson.toJson(emp), JsonObject.class) );
System.out.println("Employee-Update : "+gson.toJson(employee));
}
/*
* This method update the #target with new given value of new object in json object form
*/
public static void update(Object target, JsonObject json) throws Exception {
Gson gson=new Gson();
Class<? > class1 = target.getClass();
Set<Entry<String, JsonElement>> entrySet = json.entrySet();
for (Entry<String, JsonElement> entry : entrySet) {
String key = entry.getKey();
Field field = class1.getDeclaredField(key);
field.setAccessible(true);
Type genType = field.getGenericType();
field.set(target,
gson.fromJson(entry.getValue(),genType));
}
}
}
I'm a new java developer, and I want to develop my code with reflection.
I have a class call User:
I want to pass dynamic value to those 3 methods, so in java reflection I got some code but I don't understand why?
import .....
public class user
{
private int id;
private String name;
private Date dob;
public setID(int id)
{
this.id = id;
}
public setName(String name)
{
this.name = name;
}
public setDOB(Date dob)
{
this.dob = dob;
}
}
Class cls = Class.forName("user");
Method[] methods = cls.getDeclearedMethod();
for(Method m : methods)
{
Object[] args = new Object[1];
args[0] = .....
m.invoke(cls, args[0]);
}
I don't dare to ask why you wanna do this... this way but i hope this example helps you get the feeling of some of the capabilities of reflection provided by Java.
import java.lang.reflect.Method;
import java.util.Date;
public class Ref {
public static void main(String[] args) throws ClassNotFoundException,
InstantiationException, IllegalAccessException {
Class cls = Class.forName("User");
Object o = cls.newInstance();
Object[] fieldValues = { new Integer(1), "", new Date() };
Method[] methods = cls.getDeclaredMethods();
for (Method m : methods) {
Class[] paramTypes = m.getParameterTypes();
Object[] paramValues = new Object[1];
if (paramTypes.length == 0) {
continue;
}
if (paramTypes[0].equals(Date.class)) {
paramValues[0] = new Date();
} else if (paramTypes[0].equals(String.class)) {
paramValues[0] = "nice";
} else if (paramTypes[0].equals(Integer.TYPE)) {
paramValues[0] = 2;
}
if (paramValues[0] != null) {
try {
m.invoke(o, paramValues[0]);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} // end for
} // end for
System.out.println("o = " + o);
} // end method main
} // end class Ref
class User {
private int id;
private String name;
private Date dob;
public void setID(int id) {
this.id = id;
}
public void setName(String name) {
this.name = name;
}
public void setDOB(Date dob) {
this.dob = dob;
}
public String toString() {
return "[id = " + id + ", name = " + name + ", date = " + dob + "]";
}
}