反射技术总结

反射技术总结

1 反射技术2 Class对象3 Field类

3.1 例子 4 Method类5 反射的应用 1 反射技术

运行时动态访问对象属性方法的技术

2 Class对象

类的实例化：
之前：Car c = new Car();
现在：clazz.newInstance(); // 创建对象

public class ClassDemo {static class InnerClass{public InnerClass() {System.out.println("我是InnerClass构造方法");}public void print() {System.out.println("我是静态内部类");}}public static void main(String[] args) throws InstantiationException, IllegalAccessException {Class clazz = InnerClass.class;// 拿到Class对象InnerClass a = clazz.newInstance();// 创建对象a.print();}}

3 Field类

描述类中的属性，（数值）域

3.1 例子

public class FiledDemo {static class Car {private String brand;private String color;private double price;public String getBrand() {return brand;}public void setBrand(String brand) {this.brand = brand;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}@Overridepublic String toString() {return "Car [brand=" + brand + ", color=" + color + ", price=" + price + "]";}}public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException {Car c = new Car();c.setBrand("奇瑞QQ");c.setColor("蓝色");c.setPrice(20000.00);System.out.println(c);// 通过反射技术可以拿到private修饰的属性Class clazz = Car.class;// 拿到Car的Class对象Field[] fields = clazz.getDeclaredFields();// 通过Class对象拿到所有属性for (Field field : fields) {field.setAccessible(true);// 设置为可访问System.out.println("属性名称：" + field.getName());// 属性名称System.out.println("属性类型名称：" + field.getType().getName());// 属性类型名称System.out.println("属性类型名称简写：" + field.getType().getSimpleName());if (field.getType().getSimpleName().equals("double")) {// 修改Car的属性field.set(c, 50000.00);}}System.out.println("用反射技术修改后" + c);}}

4 Method类

public class MethodDemo {static class Car {private String brand;private String color;private double price;public void run() {System.out.println("汽车发动");}public String getBrand() {return brand;}public void setBrand(String brand) {this.brand = brand;}public String getColor() {return color;}public void setColor(String color) {this.color = color;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}@Overridepublic String toString() {return "Car [brand=" + brand + ", color=" + color + ", price=" + price + "]";}}public static void main(String[] args) throws Exception {Car c = new Car();c.setBrand("奇瑞QQ");c.setColor("蓝色");c.setPrice(20000.00);System.out.println(c);// c.run();// 大部分情况下，是创建对象后调用run()方法// 用反射的方法调用run()方法Class clazz = Car.class;// 拿到反射对象// Method[] declaredMethods = clazz.getDeclaredMethods();// 拿到所有的方法Method method = clazz.getDeclaredMethod("run");// 根据方法名和参数类型拿到对应的方法method.invoke(c);// 传入对象和参数值Method setmethod = clazz.getDeclaredMethod("setColor", String.class);// 拿到set方法,参数类型是String的class对象setmethod.invoke(c, "黑色");System.out.println(c);Method getMethod = clazz.getDeclaredMethod("getPrice");// 拿到get方法Object val = getMethod.invoke(c);System.out.println(val);}}

5 反射的应用

用反射技术自动生成sql语句

public class SQLHelper {private static volatile SQLHelper instance;private final StringBuilder sb = new StringBuilder();private SQLHelper() {}public static SQLHelper getInstance() {if (instance == null) {synchronized (SQLHelper.class) {if (instance == null) {instance = new SQLHelper();}}}return instance;}public String createInsertSQL(Object obj) {Class<?> clazz = obj.getClass();Field[] fields = clazz.getDeclaredFields();sb.append("INSERT INTO ");String tableName = clazz.getSimpleName().toLowerCase();sb.append(tableName);sb.append("(");int count = 0;try {for (Field field : fields) {field.setAccessible(true);Object retval = field.get(obj);if (retval != null) {// 有值，准备放入数据库sb.append(tableName + "_" + field.getName());sb.append(",");count++;}}sb.deleteCharAt(sb.length() - 1);sb.append(") VALUES(");for(int i = 0 ; i < count ; i ++) {sb.append("?,");}sb.deleteCharAt(sb.length() - 1);sb.append(")");} catch (Exception e) {e.printStackTrace();}return sb.toString();}}