【Java】反射
简介
通过反射的方式可以获取class对象中的属性、方法、构造函数等。
A program that can analyze the capabilities of classes is called reflective
示例代码
Person类
/**
* 测试类
* @author dj4817
* @version $Id: Person.java, v 0.1 2017/12/1 13:06 dj4817 Exp $$
*/
public class Person implements Serializable, TestInterface {
private String name;
public String address;
/**
* 私有构造器
* @param name
*/
private Person(String name) {
this.name = name;
}
/**
* 无参构造器
*/
public Person() {
}
/**
* 全参构造器
* @param name
* @param address
*/
public Person(String name, String address) {
this.name = name;
this.address = address;
}
/**
* 私有方法
*/
private void testPrivate() {
System.out.println("this is a private method");
}
@Override
public String toString() {
return "Person{" +
"name='" + name + '\'' +
", address='" + address + '\'' +
'}';
}
/**
* 接口方法
* @param s
* @return
*/
@Override
public String say(String s) {
return s;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}
Person类实现的接口
/**
* 测试接口
* @author dj4817
* @version $Id: TestInterface.java, v 0.1 2017/12/1 13:12 dj4817 Exp $$
*/
public interface TestInterface {
/**
* 接口方法
* @param s
* @return
*/
String say(String s);
}
反射测试类
/**
* Reflection tester
* @author daijiong
* @version $Id: ReflectionTest.java, v 0.1 18-9-26 下午3:12 daijiong Exp $$
*/
@RunWith(JUnit4.class)
public class ReflectionTest {
private Class personClass;
@Before
public void setUp() throws Exception {
String className = "org.djflying.bigdata.corejava.reflection.Person";
personClass = Class.forName(className);
}
@After
public void tearDown() throws Exception {
}
/**
* 获取当前加载这个类的那个类加载器对象
* @throws Exception
*/
@Test
public void testGetClassloader() throws Exception {
ClassLoader classLoader = personClass.getClassLoader();
System.out.println(classLoader.toString());
}
/**
* 打印这个类
* @throws Exception
*/
@Test
public void testPrintClass() throws Exception {
System.out.println(personClass);
System.out.println(Person.class);
}
/**
* 通过这个类创建一个实例对象，并打印实例的toString方法。
* @throws Exception
*/
@Test
public void testNewInstance() throws Exception {
Object person = personClass.newInstance();
System.out.println(person);
}
/**
* 获取这个类的非私有的构造函数
* @throws Exception
*/
@Test
public void testGetConstructor() throws Exception {
Constructor constructor = personClass.getConstructor(String.class, String.class);
System.out.println(constructor.toString());
}
/**
* 获取这个类的私有的构造函数
* @throws Exception
*/
@Test
public void testGetDeclaredConstructor() throws Exception {
Constructor declaredConstructor = personClass.getDeclaredConstructor(String.class);
System.out.println(declaredConstructor.toString());
}
/**
* 根据这个构造函数创建实例，并打印实例的toString方法。
* @throws Exception
*/
@Test
public void testConstructor() throws Exception {
Constructor constructor = personClass.getConstructor(String.class, String.class);
Object person = constructor.newInstance("david", "suzhou");
System.out.println(person);
Constructor declaredConstructor = personClass.getDeclaredConstructor(String.class);
// 强制取消Java的权限检测，不然会报错
declaredConstructor.setAccessible(true);
Object person2 = declaredConstructor.newInstance("david");
System.out.println(person2);
}
/**
* 访问非私有的成员变量
* @throws Exception
*/
@Test
public void testGetField() throws Exception {
Field field = personClass.getField("address");
Object person = personClass.getConstructor().newInstance();
field.set(person, "suzhou");
System.out.println(field.get(person));
}
/**
* 访问私有的成员变量
* @throws Exception
*/
@Test
public void testGetDeclaredField() throws Exception {
Field declaredField = personClass.getDeclaredField("name");
// 强制取消Java的权限检测，不然会报错
declaredField.setAccessible(true);
Object person = personClass.getConstructor().newInstance();
declaredField.set(person, "david");
System.out.println(declaredField.get(person));
}
/**
* 获取非私有的成员函数
* @throws Exception
*/
@Test
public void testGetMethod() throws Exception {
Method method = personClass.getMethod("toString");
Object person = personClass.getConstructor().newInstance();
Object invoke = method.invoke(person);
System.out.println(invoke);
}
/**
* 获取私有的成员函数
* @throws Exception
*/
@Test
public void testGetDeclaredMethod() throws Exception {
Method declaredMethod = personClass.getDeclaredMethod("testPrivate");
// 强制取消Java的权限检测，不然会报错
declaredMethod.setAccessible(true);
Object person = personClass.getConstructor().newInstance();
Object invoke = declaredMethod.invoke(person);
System.out.println(invoke);
}
/**
* 获取某个类实现的所有接口
* @throws Exception
*/
@Test
public void testGetInterface() throws Exception {
Class[] interfaces = personClass.getInterfaces();
for (Class intf : interfaces) {
System.out.println(intf);
}
}
/**
* 反射当前这个类的直接父类
* @throws Exception
*/
@Test
public void testGetGenericSuperclass() throws Exception {
Type genericSuperclass = personClass.getGenericSuperclass();
System.out.println(genericSuperclass);
}
/**
* 判断当前的Class对象表示是否是数组
* @throws Exception
*/
@Test
public void testIsArray() throws Exception {
boolean isArray = personClass.isArray();
System.out.println(isArray);
}
/**
* 判断当前的Class对象表示是否是枚举类
* @throws Exception
*/
@Test
public void testIsEnum() throws Exception {
boolean isEnum = personClass.isEnum();
System.out.println(isEnum);
}
/**
* 判断当前的Class对象表示是否是接口
* @throws Exception
*/
@Test
public void testIsInterface() throws Exception {
boolean isInterface = personClass.isInterface();
System.out.println(isInterface);
}
/**
* 使用getResourceAsStream加载资源文件
* @throws Exception
*/
@Test
public void testGetResourceAsStream() throws Exception {
InputStream resourceAsStream = personClass.getResourceAsStream("log4j.properties");
}
}
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