一、反射

1.1、反射的概述

什么是反射?

反射允许对成员变量，成员方法和构造方法的信息进行编程访问

1.2、获取class对象的三种方式

1. Class.forName(“全类名”);
   • 全类名：包名+类名
2. 类名.class
3. 对象.getclass()
   

package reflect.Dome1;public class Dome {public static void main(String[] args) throws ClassNotFoundException {//方式一Class aClass = Class.forName("reflect.Dome1.student");System.out.println(aClass);//方式二Class aClass1 = student.class;System.out.println(aClass1);//与方式一的结果相同student s = new student();Class aClass2 = s.getClass();System.out.println(aClass2);//三个方式结果相同}
}
package reflect.Dome1;public class student {private String name;private int age;public student() {}public student(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String toString() {return "student{name = " + name + ", age = " + age + "}";}
}

1.3、反射获取构造方法

Class类中用于获取构造方法的方法

方法名称	说明
Constructor<?>[ ] getConstructors()	返回所有公共构造方法对象的数组
Constructor<?>[ ] getDeclaredConstructors()	返回所有构造方法对象的数组
Constructor<T> getConstructor(Class<?>… parameterTypes)	返回单个公共构造方法对象
Constructor<T> getDeclaredConstructor(Class<?>… parameterTypes)	返回单个构造方法对象

Constructor类中用于创建对象的方法

方法名称	说明
T newlnstance(Object… initargs)	根据指定的构造方法创建对象
setAccessible(boolean flag)	设置为true,表示取消访问权限

package reflect.Dome2;import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;public class dome {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {Class class1 = Class.forName("reflect.Dome2.student");Constructor[] constructors = class1.getConstructors();for (Constructor constructor : constructors) {System.out.println(constructor);}Constructor con = class1.getDeclaredConstructor(String.class,int.class);System.out.println(con);Constructor[] declaredConstructors = class1.getDeclaredConstructors();for (Constructor declaredConstructor : declaredConstructors) {System.out.println(declaredConstructor);}//如果是私有构造方法，则不能直接使用，只能看到//通过添加setAccessible方法，暴力取消临时权限校验。就可以使用con.setAccessible(true);student stu = (student) con.newInstance("张三", 21);System.out.println(stu);}
}
package reflect.Dome2;public class student {private String name;private int age;public student() {}private student(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String toString() {return "student{name = " + name + ", age = " + age + "}";}
}

1.4、反射获取成员变量

Class类中用于获取成员变量的方法

方法名称	说明
Field[] getFields()	返回所有公共成员变量对象的数组
Field[] getDeclaredFields()	返回所有成员变量对象的数组
Field getField(String name)	返回单个公共成员变量对象
Field getDeclaredField(String name)	返回单个成员变量对象

Field类中用于创建对象的方法

方法名称	说明
void set(Object obj, Object value)	赋值
Object get(Object obj)	获取值

package reflect.Dome3;import java.lang.reflect.Field;public class dome {public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException, IllegalAccessException {Class clazz = Class.forName("reflect.Dome3.Student");//获取到公共成员变量Field[] fields = clazz.getFields();for (Field field : fields) {System.out.println(field);}//查找该成员变量Field gender = clazz.getField("gender");System.out.println(gender);//获取所有的成员变量Field[] declaredField = clazz.getDeclaredFields();for (Field field : declaredField) {System.out.println(field);}//获取私有变量Field name = clazz.getDeclaredField("name");System.out.println(name);//获取权限修饰符int modifiers = name.getModifiers();System.out.println(modifiers);//获取成员变量的名称String name1 = name.getName();System.out.println(name1);//获取成员变量的类型Class<?> type = name.getType();System.out.println(type);//创建一个对象Student s = new Student("张三",23,"男");name.setAccessible(true);Object o = name.get(s);System.out.println(o);//修改s里面name的值name.set(s,"小王");System.out.println(s);}
}
package reflect.Dome3;public class Student {private String name;private int age;public String gender;public Student() {}public Student(String name, int age, String gender) {this.name = name;this.age = age;this.gender = gender;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getGender() {return gender;}public void setGender(String gender) {this.gender = gender;}public String toString() {return "Student{name = " + name + ", age = " + age + ", gender = " + gender + "}";}
}

1.5、反射获取成员方法

Class类中用于获取成员方法的方法

方法名称	说明
Method[] getMethods()	返回所有公共成员方法对象的数组，包括继承的
Method[] getDeclaredMethods()	返回所有成员方法对象的数组，不包括继承的
Method getMethod(String name, Class<?>… parameterTypes)	返回单个公共成员方法对象
Method getDeclaredMethod(String name, Class<?>… parameterTypes)	返回单个成员方法对象

Method类中用于创建对象的方法

方法名称	说明
Object invoke(Object obj, Object… args)	运行方法

参数一：用obj对象调用该方法
参数二：调用方法的传递的参数（如果没有就不写)
返回值：方法的返回值（如果没有就不写)

package reflect.Dome4;import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;public class dome {public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {Class aClass = Class.forName("reflect.Dome4.student");//包括父类的方法Method[] methods = aClass.getMethods();for (Method method : methods) {System.out.println(method);}System.out.println("===================================");//不包括父类的方法Method[] declaredMethods = aClass.getDeclaredMethods();for (Method declaredMethod : declaredMethods) {System.out.println(declaredMethod);}System.out.println("===================================");//返回单个公共成员方法变量Method getAge = aClass.getMethod("setAge", int.class);System.out.println(getAge);System.out.println("===================================");//返回单个成员方法对象Method eat = aClass.getDeclaredMethod("eat", String.class);System.out.println(eat);//返回方法的名称System.out.println("===================================");String name = eat.getName();System.out.println(name);System.out.println("===================================");Class<?> declaringClass = eat.getDeclaringClass();System.out.println(declaringClass);System.out.println("===================================");//返回方法里面的参数Parameter[] parameters = eat.getParameters();for (Parameter parameter : parameters) {System.out.println(parameter);}System.out.println("===================================");//返回方法抛出的异常Class<?>[] exceptionTypes = eat.getExceptionTypes();for (Class<?> exceptionType : exceptionTypes) {System.out.println(exceptionType);}//利用反射运行方法student s = new student("xiaowang",23,'男');eat.setAccessible(true);//没有返回值就不需要写//eat.invoke(s, "烧烤");//果如有返回值就需要写String o = (String) eat.invoke(s, "烧烤");System.out.println(o);}
}
package reflect.Dome4;import java.io.IOException;public class student {private String name;private int age;public char gender;public student() {}public student(String name, int age, char gender) {this.name = name;this.age = age;this.gender = gender;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public char getGender() {return gender;}public void setGender(char gender) {this.gender = gender;}private String eat(String str) throws IOException,RuntimeException,ArithmeticException {System.out.println(getName()+"正在吃"+str);return "奥利给";}public String toString() {return "student{name = " + name + ", age = " + age + ", gender = " + gender + "}";}
}

1.6、综合练习

反射的作用：

1. 获取一个类里面所有的信息，获取到了之后，再执行其他的业务逻辑
2. 结合配置文件，动态的创建对象并调用方法

1.6.1、保存信息

package reflect.Dome5;import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.lang.reflect.Field;public class dome {public static void main(String[] args) throws IllegalAccessException, IOException {student s = new student("小明",18,181.0,"玩");teacher t = new teacher("王老师",30);printClass(t);}public static void printClass(Object obj) throws IllegalAccessException, IOException {Class aClass = obj.getClass();//创建IO流BufferedWriter bw = new BufferedWriter(new FileWriter("D:\\Java\\IDEA\\代码文件\\Three\\a.txt"));Field[] declaredFields = aClass.getDeclaredFields();for (Field declaredField : declaredFields) {//进行修饰符忽略declaredField.setAccessible(true);//获取到该变量的名字String name = declaredField.getName();//获取到该变量的值Object value = declaredField.get(obj);//写出数据bw.write(name+"="+value);bw.newLine();System.out.println(name+"="+value);}bw.flush();bw.close();}
}
package reflect.Dome5;public class student {private String name;private int age;private double height;private String hobby;public student() {}public student(String name, int age, double height, String hobby) {this.name = name;this.age = age;this.height = height;this.hobby = hobby;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}urn height*/public double getHeight() {return height;}public void setHeight(double height) {this.height = height;}public String getHobby() {return hobby;}public void setHobby(String hobby) {this.hobby = hobby;}public String toString() {return "student{name = " + name + ", age = " + age + ", height = " + height + ", hobby = " + hobby + "}";}
}
package reflect.Dome5;public class teacher {private String name;private int age;public teacher() {}public teacher(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String toString() {return "teacher{name = " + name + ", age = " + age + "}";}
}

1.6.2、跟配置文件结合动态创建

package reflect.Dome6;import java.io.FileInputStream;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Properties;public class dome {public static void main(String[] args) throws IOException, ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {//读取配置文件中的信息Properties prop = new Properties();FileInputStream fis = new FileInputStream("prop.properies");//读取的文件prop.load(fis);fis.close();System.out.println(prop);//获取全类名和方法名Object classname = prop.get("classname");Object method = prop.get("method");System.out.println(classname);System.out.println(method);//利用反射创建对象并运行方法Class<?> aClass = Class.forName((String) classname);//获取构造方法Constructor con = aClass.getDeclaredConstructor();Object o = con.newInstance();System.out.println(o);//获取成员方法并运行Method declaredMethod = aClass.getDeclaredMethod((String) method);declaredMethod.setAccessible(true);declaredMethod.invoke(o);}
}
package reflect.Dome6;public class student {private String name;private int age;private char gender;public student() {}public student(String name, int age, char gender) {this.name = name;this.age = age;this.gender = gender;}public void study(){System.out.println("正在学习");}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public char getGender() {return gender;}public void setGender(char gender) {this.gender = gender;}public String toString() {return "student{name = " + name + ", age = " + age + ", gender = " + gender + "}";}
}
classname=reflect.Dome6.student
method=study