一文搞懂Spring中的注解与反射

public class CustomAnnotation {

    
    @MyAnnotation(value = "解释")
    public void test(){
    }
}

//自定义注解必须的元注解target，指明注解的作用域（此处指明的是在类和方法上起作用）
@Target({ElementType.TYPE,ElementType.METHOD})
//元注解retention声明该注解在何时起作用（此处指明的是在运行时起作用）
@Retention(RetentionPolicy.RUNTIME)
@interface MyAnnotation{

    //注解中需声明参数，格式为：参数类型 + 参数名();
    String value() default "";

}

function f(){
    var x = "var a = 3; var b = 5; alert(a+b)";
    eval(x)
}

Class c = Class.forName("java.lang.String")

public class ReflectionTest extends Object{
    public static void main(String[] args) throws ClassNotFoundException {
        //通过反射获取类的Class对象
        Class c = Class.forName("com.dcone.zhuzqc.demo.User");
        //一个类在内存中只有唯一个Class对象
        System.out.println(c.hashCode());

    }
}


@Data
class User{
    private String userName;
    private Long userId;
    private Date loginTime;
}

@HotSpotIntrinsicCandidate
public final native Class<?> getClass();

//类的class属性
Class classOne = User.class;

   //已有类对象的getClass方法
   Class collatz = user.getClass();

Class c = Class.forName("com.dcone.zhuzqc.demo.User");

//内置对象才有的TYPE属性，较大的局限性
Class<Integer> type = Integer.TYPE;

//类可以反射
    Class c1 = Person.class;

//接口可以反射
     Class c2 = Comparable.class;

//数组可以反射
     Class c3 = String[].class;
     Class c4 = int[][].class;

//枚举可以反射
     Class c6 = ElementType.class;

//注解可以反射
     Class c5 = Data.class;

//基本数据类型(包装类)可以反射
     Class c7 = int.class;
     Class c8 = Integer.class;

//void可以反射
     Class c9 = void.class;

public class Test03 {
    public static void main(String[] args) {
        //获取系统类的加载器
        ClassLoader sysLoader = ClassLoader.getSystemClassLoader();
        System.out.println(sysLoader);

        //获取系统类的父类加载器
        ClassLoader parent = sysLoader.getParent();
        System.out.println(parent);
    }
}

public class Test04 {
    public static void main(String[] args) throws ClassNotFoundException {
        Class c1 = Class.forName("com.dcone.zhuzqc.demo.User");
        //获取所有属性
        Field field[];
        field = c1.getDeclaredFields();
        for (Field f:field){
            System.out.println(f);
        }
        //获得类的方法
        Method method[];
        method = c1.getDeclaredMethods();
        for (Method m:method){
            System.out.println(m);
        }
    }
}

public class Demo {
    public static void main(String[] args) throws NoSuchMethodException, NoSuchFieldException {
 
        // 获取成员方法参数的泛型类型信息
        getMethodParametricGeneric();
    }

 
    public static void getMethodParametricGeneric() throws NoSuchMethodException {
        // 获取MyTestClass类中名为"setList"的方法
        Method setListMethod = MyClass.class.getMethod("setList", List.class);
        // 获取该方法的参数类型信息（带有泛型）
        Type[] genericParameterTypes = setListMethod.getGenericParameterTypes();
        // 但我们实际上需要获取返回值类型中的泛型信息，所以要进一步判断，即判断获取的返回值类型是否是参数化类型ParameterizedType
        for (Type genericParameterType : genericParameterTypes) {
            ParameterizedType parameterizedType = (ParameterizedType) genericParameterType;
            // 获取成员方法参数的泛型类型信息
            Type[] actualTypeArguments = parameterizedType.getActualTypeArguments();
            for (Type actualTypeArgument : actualTypeArguments) {
                Class realType = (Class) actualTypeArgument;
                System.out.println("成员方法参数的泛型信息：" + realType);
            }
        }
    }

@Data
class User{
    @ApiModelProperty(value = "姓名")
    private String userName;

    @ApiModelProperty(value = "用户id")
    private Long userId;

    @ApiModelProperty(value = "登录时间")
    private Date loginTime;
}

//如果指定类型的注释存在于此元素上,  方法返回true 
java.lang.Package.isAnnotationPresent(Class<? extends Annotation> annotationClass) 
//如果是该类型的注释, 方法返回该元素的该类型的注释
java.lang.Package.getAnnotation(Class< A > annotationClass) 

    public static void main(String[] args) throws ClassNotFoundException {
        Class c1 = Class.forName("com.dcone.zhuzqc.demo.User");

        if(User.class.isAnnotationPresent(ApiModel.class)){
            System.out.println(User.class.getAnnotation(ApiModel.class).value());
        }
        // 获取类变量注解
        Field[] fields = User.class.getDeclaredFields();
        for (Field f : fields) {
            if(f.isAnnotationPresent(ApiModelProperty.class)){
                System.out.print(f.getAnnotation(ApiModelProperty.class).name() + ",");
            }
        }
    }

    @Bean("sqlSessionFactory")
    public String test(@RequestBody User user) throws ClassNotFoundException {
        Class c2 = Class.forName("com.dcone.zhuzqc.demo.User");
        // 获取方法注解：
        Method[] methods = User.class.getDeclaredMethods();
        for(Method m : methods){
            if (m.isAnnotationPresent((Class<? extends Annotation>) User.class)) {
                System.out.println(m.getAnnotation(ApiModelProperty.class).annotationType());
            }
        }
        return "test";
    }

    @Bean("sqlSessionFactory")
    public String test(@RequestBody User user) throws ClassNotFoundException {
        Class c2 = Class.forName("com.dcone.zhuzqc.demo.User");
        // 获取方法参数注解
        Method[] methods2 = User.class.getDeclaredMethods();
        for (Method m : methods2) {
            // 获取方法的所有参数
            Parameter[] parameters = m.getParameters();
            for (Parameter p : parameters) {
                // 判断是否存在注解
                if (p.isAnnotationPresent(ApiModelProperty.class)) {
                    System.out.println(p.getAnnotation(ApiModelProperty.class).name());
                }
            }
        }
        return "test";
    }