Java动态处理类常用方法

一、简介

工作中经常会遇到动态处理类及属性的场景，在此处记录下常用方法。

1、依赖的jar

部分样例方法依赖的jar有：

• Apache Commons BeanUtils

下载

或使用Maven：

<dependency>
    <groupId>commons-beanutils</groupId>
    <artifactId>commons-beanutils</artifactId>
    <version>1.9.3</version>
</dependency>

• Apache Commons Logging

下载

2、模型类

样例使用到的模型相关类有：

Animal:

public class Animal {

	private String id;
	private String name;
	private List<Animal> children = new ArrayList<>();
	
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public List<Animal> getChildren() {
		return children;
	}
	public void setChildren(List<Animal> children) {
		this.children = children;
	}
	
}

Mammal:

public class Mammal extends Animal{

	private Nest nest;
	private boolean male;
	
	public Nest getNest() {
		return nest;
	}
	public void setNest(Nest nest) {
		this.nest = nest;
	}
	public boolean isMale() {
		return male;
	}
	public void setMale(boolean male) {
		this.male = male;
	}
	
}

Nest:

public class Nest {

	private int size;
	private String color;
	
	public int getSize() {
		return size;
	}
	public void setSize(int size) {
		this.size = size;
	}
	public String getColor() {
		return color;
	}
	public void setColor(String color) {
		this.color = color;
	}
	
}

Dog:

public class Dog extends Mammal{

	private Map<String, Animal> friends = new HashMap<>();

	public Map<String, Animal> getFriends() {
		return friends;
	}

	public void setFriends(Map<String, Animal> friends) {
		this.friends = friends;
	}
	
}

二、常用方法

1、判断对象是否可读写某个属性

• 方法定义：

PropertyUtils.isReadable(Object bean, String name)

PropertyUtils.isWriteable(Object bean, String name)

• 样例：

public static void main(String[] args) {
	Dog dog = new Dog();
	System.out.println(PropertyUtils.isReadable(dog, "id"));
	System.out.println(PropertyUtils.isWriteable(dog, "name"));
}

• 输出:

true
true

2、对象普通属性的赋值与取值

• 方法定义：

设置指定bean的某个属性的值：

PropertyUtils.setProperty(Object bean, String name, Object value)

设置指定bean的某个(可能是嵌套的)属性的值：

PropertyUtils.setNestedProperty(Object bean, String name, Object value)

返回指定bean的某个属性的值：

PropertyUtils.getProperty(Object bean, String name)

返回指定bean的某个(可能是嵌套的)属性的值：

PropertyUtils.getNestedProperty(Object bean, String name)

• 样例：

public static void main(String[] args) {
	try {
		Dog dog = new Dog();
		Nest nest = new Nest();
		dog.setNest(nest);
		
		PropertyUtils.setProperty(dog, "id", "007");
		PropertyUtils.setNestedProperty(dog, "nest.color", "pink");
		PropertyUtils.setProperty(dog, "name", "super dog");
		
		System.out.println(PropertyUtils.getProperty(dog, "id"));
		System.out.println(PropertyUtils.getNestedProperty(dog, "nest.color"));
		System.out.println(PropertyUtils.getNestedProperty(dog, "name"));
	} catch (Exception e) {
		e.printStackTrace();
	}
}

• 输出：

007
pink
super dog

3、对象集合属性的赋值与取值

• 方法定义：

获取指定bean的Map属性某个key的值：

PropertyUtils.getMappedProperty(Object bean, String name, String key)

设置指定bean的Map属性某个key的值：

PropertyUtils.setMappedProperty(Object bean, String name, String key, Object value)

获取指定bean的List属性指定索引位置元素的值：

PropertyUtils.getIndexedProperty(Object bean, String name, int index)

设置指定bean的List属性指定索引位置元素的值：

PropertyUtils.setIndexedProperty(Object bean, String name, int index, Object value)

• Map样例

public static void main(String[] args) {
	try{
		String field = "friends";
		Dog dog = new Dog();
		dog.setName("Tom");
		
		Dog abel = new Dog();
		abel.setName("Abel");
		dog.getFriends().put(abel.getName(), abel);
		
		Dog ben = new Dog();
		ben.setName("Ben");
		PropertyUtils.setMappedProperty(dog, field, "AAA", ben);
		
		Dog friend = (Dog) PropertyUtils.getMappedProperty(dog, field, "Abel");
		System.out.println(friend.getName());
		
		friend = (Dog) PropertyUtils.getMappedProperty(dog, field, "AAA");
		System.out.println(friend.getName());
	}catch(Exception e){
		e.printStackTrace();
	}
}

输出：

Abel
Ben

• List样例

public static void main(String[] args) {
	try{
		String field = "children";
		Dog dog = new Dog();
		dog.setName("Tom");
		dog.getChildren().add(null);
		dog.getChildren().add(null);
	
		Dog one = new Dog();
		one.setName("a child");
		
		Dog another = new Dog();
		another.setName("another child");
		
		PropertyUtils.setIndexedProperty(dog, field, 0, one);
		PropertyUtils.setIndexedProperty(dog, field, 1, another);
		
		Dog child = (Dog) PropertyUtils.getIndexedProperty(dog, field, 0);
		System.out.println(child.getName());
		child = (Dog) PropertyUtils.getIndexedProperty(dog, field, 1);
		System.out.println(child.getName());
	}catch(Exception e){
		e.printStackTrace();
	}
}

输出：

a child
another child

4、获取某个类或对象的属性描述符

• 方法定义：

PropertyUtils.getPropertyDescriptors(Class<?> beanClass)

PropertyUtils.getPropertyDescriptors(Object bean)

• 样例：

public static void main(String[] args) {
	PropertyDescriptor[] descriptors = PropertyUtils.getPropertyDescriptors(Dog.class);
	for(PropertyDescriptor descriptor : descriptors){
		System.out.println(String.format("%s\t%s", descriptor.getName(), descriptor.getPropertyType()));
	}
}

• 输出：

children	interface java.util.List
name	class java.lang.String
id	class java.lang.String
nest	class com.bean.model.Nest
class	class java.lang.Class
friends	interface java.util.Map
male	boolean

5、获取某个类的所有字段

与上面类似，下面的方法也支持获取继承的属性：

public static List<Field> getFields(Class<?> clazz){
	List<Field> fields = new ArrayList<>();
	while(clazz != null){
		Field[] declaredFields = clazz.getDeclaredFields();
		for(Field field : declaredFields){
			//过滤掉static属性
			if(Modifier.isStatic(field.getModifiers())){
				continue;
			}
			fields.add(field);
		}
		clazz = clazz.getSuperclass();
	}
	return fields;
}

• 测试方法：

public static void main(String[] args) {
	List<Field> fields = getFields(Dog.class);
	for(Field field : fields){
		System.out.println(String.format("%s\t%s", field.getName(), field.getType()));
	}
}

• 输出：

friends	interface java.util.Map
nest	class com.bean.model.Nest
male	boolean
id	class java.lang.String
name	class java.lang.String
children	interface java.util.List

6、获取集合元素的类型

public static Class<?> getListItemClass(Class<?> clazz, String property) {
	try {
		Field field = clazz.getDeclaredField(property);
		Type genericType = field.getGenericType();
		if(genericType instanceof ParameterizedType){
			ParameterizedType itemType = (ParameterizedType) genericType;
			Class<?> itemClass = (Class<?>) itemType.getActualTypeArguments()[0];
			return itemClass;
		}
	}catch (Exception e) {
		e.printStackTrace();
	}
	return null;
}

• 测试方法：

private static void test03() {
	Class<?> itemClass = getListItemClass(Animal.class, "children");
	System.out.println(itemClass);
}

• 输出：

class com.bean.model.Animal

7、动态创建集合及元素

• 样例

public static void main(String[] args) {
	 try {
		//动态创建对象
		Animal animal = Animal.class.newInstance();
		PropertyUtils.setProperty(animal, "id", "001");
		PropertyUtils.setProperty(animal, "name", "Tom");
		//动态创建集合
		List<Object> children = ArrayList.class.newInstance();
		PropertyUtils.setProperty(animal, "children", children);
		Class<?> itemType = getListItemClass(Animal.class, "children");
		//创建集合元素
		Object child = itemType.newInstance();
		PropertyUtils.setProperty(child, "name", "Tom's baby");
		children.add(child);
		
		System.out.println(String.format("ID: %s, Name: %s", animal.getId(), animal.getName()));
		for(Animal item : animal.getChildren()){
			System.out.println("Child Name: " + item.getName());
		}
	} catch (Exception e) {
		e.printStackTrace();
	}
}

• 输出：

ID: 001, Name: Tom
Child Name: Tom's baby

参考资料：

• Apache Commons BeanUtils

• org.apache.commons.beanutils

• PropertyUtils

• 使用PropertyUtils访问Bean属性