Reflect
Java反射機制時在運行狀態(tài)中张肾，對于任意一個類管宵，都能知道這個類所有的屬性和方法截珍；對于任意一個對象，都能調(diào)用它的任意一個方法和屬性箩朴；這種動態(tài)獲取信息以及動態(tài)調(diào)用對象的方法的功能稱為Java語言的反射機制岗喉。（就是通過class文件對象，使用該文件中的成員變量炸庞、構(gòu)造方法钱床、成員方法）
獲取class文件對象（Class）
- Object類中的getClass()方法
- 數(shù)據(jù)類型的靜態(tài)屬性class
- Class.forName("類路徑")
public class Student {
private String name;
Integer age;
public String addr;
public Student() {
}
public Student(String name, Integer age, String addr) {
this.name = name;
this.age = age;
this.addr = addr;
}
private Student(String addr) {
this.addr = addr;
}
public String method(String s) {
return String.format("method_%s", s);
}
void show() {
System.out.println("student show");
}
private void test() {
System.out.println("student test ");
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
", addr='" + addr + '\'' +
'}';
}
}
public class ReflectDemo {
public static void main(String[] args) throws ClassNotFoundException {
// Object類中的getClass()方法
Student student = new Student();
Class<? extends Student> aClass = student.getClass();
// 數(shù)據(jù)類型的靜態(tài)屬性class
Class<Student> bClass = Student.class;
// Class.forName("類路徑")
Class<?> cClass = Class.forName("com.net.reflect.Student");
// 三種方式獲取的是同一個class文件對象
// true
System.out.println(aClass == bClass);
// true
System.out.println(bClass == cClass);
}
}
獲取構(gòu)造方法并使用
public class ReflectDemo2 {
public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
// 獲取字節(jié)碼文件對象
Class<Student> studentClass = Student.class;
// 獲取所有公共構(gòu)造方法
Constructor<?>[] constructors = studentClass.getConstructors();
for (Constructor<?> constructor : constructors) {
System.out.println(constructor);
}
// 獲取所有構(gòu)造方法
Constructor<?>[] declaredConstructors = studentClass.getDeclaredConstructors();
for (Constructor<?> declaredConstructor : declaredConstructors) {
System.out.println(declaredConstructor);
}
// 獲取指定構(gòu)造方法并使用
Constructor<Student> declaredConstructor = studentClass.getDeclaredConstructor(String.class, Integer.class, String.class);
System.out.println(declaredConstructor);
// 創(chuàng)建實例
Student student = declaredConstructor.newInstance("zhansan", 11, "aaa");
System.out.println(student);
// 獲取私有方法并使用
Constructor<Student> con = studentClass.getDeclaredConstructor(String.class);
// 設置訪問權(quán)限
con.setAccessible(true);
// 創(chuàng)建實例
Student student1 = con.newInstance("bbb");
System.out.println(student1);
}
}
獲取成員變量并使用
public class ReflectField {
public static void main(String[] args) throws NoSuchFieldException, NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
// 獲取字節(jié)碼文件對象
Class<Student> studentClass = Student.class;
// 獲取所有公開的成員變量
// public java.lang.String com.net.mybatisplus.reflect.Student.addr
Field[] fields = studentClass.getFields();
for (Field field : fields) {
System.out.println(field);
}
// 獲取所有成員變量
// private java.lang.String com.net.mybatisplus.reflect.Student.name
// java.lang.Integer com.net.mybatisplus.reflect.Student.age
// public java.lang.String com.net.mybatisplus.reflect.Student.addr
Field[] declaredFields = studentClass.getDeclaredFields();
for (Field declaredField : declaredFields) {
System.out.println(declaredField);
}
// 獲取單個公開成員變量并對其賦值
Constructor<Student> constructor = studentClass.getConstructor();
Student student = constructor.newInstance();
Field addr = studentClass.getField("addr");
addr.set(student, "ccc");
// Student{name='null', age=null, addr='ccc'}
System.out.println(student);
// 獲取單個私有成員變量并對其賦值
Field name = studentClass.getDeclaredField("name");
name.setAccessible(true);
name.set(student, "zhangsan");
// Student{name='zhangsan', age=null, addr='ccc'}
System.out.println(student);
}
}
獲取成員方法并使用
public class ReflectMethod {
public static void main(String[] args) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
// 獲取字節(jié)碼文件對象
Class<Student> studentClass = Student.class;
// 獲取所有公開方法（包括父類）
Method[] methods = studentClass.getMethods();
for (Method method : methods) {
System.out.println(method);
}
System.out.println("-----------------");
// 獲取所有方法（不包括父類）
Method[] declaredMethods = studentClass.getDeclaredMethods();
for (Method declaredMethod : declaredMethods) {
System.out.println(declaredMethod);
}
System.out.println("-----------------");
// 獲取單個公開方法并使用
Constructor<Student> constructor = studentClass.getConstructor();
Student student = constructor.newInstance();
Method method = studentClass.getMethod("method", String.class);
Object stuMethod = method.invoke(student, "stuMethod");
System.out.println(stuMethod);
System.out.println("-----------------");
// 獲取單個私有方法并使用
Method test = studentClass.getDeclaredMethod("test");
test.setAccessible(true);
test.invoke(student);
}
}
工具類
public class ReflectTool {
// 賦值對象的任意屬性
public static void setProperty(Object obj, String propertyName, Object value)
throws NoSuchFieldException, IllegalAccessException {
// 獲取字節(jié)碼文件對象
Class<?> aClass = obj.getClass();
// 獲取成員變量
Field declaredField = aClass.getDeclaredField(propertyName);
// 取消訪問檢查
declaredField.setAccessible(true);
// 賦值
declaredField.set(obj, value);
}
}
反射越過泛型檢查
public class ListReflect {
public static void main(String[] args) throws NoSuchMethodException, InvocationTargetException, IllegalAccessException {
List<Integer> list = Lists.newArrayList();
Class<? extends List> aClass = list.getClass();
Method add = aClass.getDeclaredMethod("add", Object.class);
add.setAccessible(true);
add.invoke(list, "list1");
add.invoke(list, 11);
add.invoke(list, true);
System.out.println(list);
}
}
