反射获取泛型，操作注解

通过反射获取泛型

import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.List;
import java.util.Map;

public class ObtainGeneric {
    public void test01(Map<String,User> map, List<User> list){
        System.out.println("test01");
    }
    public Map<String,User> test02(){
        System.out.println("test02");
        return null;
    }
    public static void main(String[] args) throws NoSuchMethodException {
        Method method = ObtainGeneric.class.getMethod("test01",Map.class,List.class);
        Type[] genericParameterTypes = method.getGenericParameterTypes();
        for(Type genericParameterType:genericParameterTypes){
            System.out.println("#"+genericParameterType);
//获取参数类型
            Type[] actualTypeArguments = ((ParameterizedType)genericParameterType).getActualTypeArguments();
            for(Type actualTypeArgument:actualTypeArguments){
                System.out.println(actualTypeArgument);
            }
        }
    }

}

反射操作注解

import java.lang.annotation.*;
import java.lang.reflect.Field;

public class Test12 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class c1 = Class.forName("reflection.Student2");
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations){
            System.out.println(annotation);
        }
        TableCheng tableCheng = (TableCheng)c1.getAnnotation(TableCheng.class);
        String value = tableCheng.value();
        System.out.println(value);

        //获得指定类的注解
        Field f = c1.getDeclaredField("name");
        FieldCheng annotation = f.getAnnotation(FieldCheng.class);
        System.out.println(annotation.columnName());
        System.out.println(annotation.type());
        System.out.println(annotation.type());



    }
}
@TableCheng("db_student")
class Student2 {
    @FieldCheng(columnName = "db_id",type = "int", length = 10)
    private int id;
    @FieldCheng(columnName = "db_age",type = "int", length = 10)
    private int age;
    @FieldCheng(columnName = "db_name",type = "varchar", length = 30)
    private String name;

    public Student2() {
    }

    public Student2(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface TableCheng{
    String value();
}

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface FieldCheng{
    String columnName();
    String type();
    int length();
}
result:

E:\JAVA\JDK\bin\java.exe "-javaagent:E:\IDEA\IntelliJ IDEA 2019.3.3\lib\idea_rt.jar=55359:E:\IDEA\IntelliJ IDEA 2019.3.3\bin" -Dfile.encoding=UTF-8 -classpath E:\IDEA\Annotation\out\production\Annotation reflection.Test12
@reflection.TableCheng("db_student")
db_student
db_name
varchar
varchar

Process finished with exit code 0