反射技术总结
1 反射技术
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<InnerClass> clazz = InnerClass.class;// 拿到Class对象
InnerClass a = clazz.newInstance();// 创建对象
a.print();
}
}
3 Field类
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;
}
@Override
public 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<Car> 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;
}
@Override
public 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<Car> 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;
}
/**
* 自动生成sql语句
* INSERT INTO 表名(car_brand,car_color,car_price) values(?,?,?)
*
* @param obj
* @return
*/
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();
}
}
