public class AnnotationDemo {
  //@Test注解修饰方法A
  @Test
  public static void A(){
    System.out.println("Test.....");
  }

  //一个方法上可以拥有多个不同的注解
  @Deprecated
  @SuppressWarnings("uncheck")
  public static void B(){

  }
}

//声明Test注解
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Test {

} 

public enum ElementType {
  /**标明该注解可以用于类、接口（包括注解类型）或enum声明*/
  TYPE,

  /** 标明该注解可以用于字段(域)声明，包括enum实例 */
  FIELD,

  /** 标明该注解可以用于方法声明 */
  METHOD,

  /** 标明该注解可以用于参数声明 */
  PARAMETER,

  /** 标明注解可以用于构造函数声明 */
  CONSTRUCTOR,

  /** 标明注解可以用于局部变量声明 */
  LOCAL_VARIABLE,

  /** 标明注解可以用于注解声明(应用于另一个注解上)*/
  ANNOTATION_TYPE,

  /** 标明注解可以用于包声明 */
  PACKAGE,

  /**
   * 标明注解可以用于类型参数声明（1.8新加入）
   * @since 1.8
   */
  TYPE_PARAMETER,

  /**
   * 类型使用声明（1.8新加入)
   * @since 1.8
   */
  TYPE_USE
}

@Inherited
@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface DocumentA {
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface DocumentB {
}

@DocumentA
class A{ }

class B extends A{ }

@DocumentB
class C{ }

class D extends C{ }

//测试
public class DocumentDemo {

  public static void main(String... args){
    A instanceA=new B();
    System.out.println("已使用的@Inherited注解:"+Arrays.toString(instanceA.getClass().getAnnotations()));

    C instanceC = new D();

    System.out.println("没有使用的@Inherited注解:"+Arrays.toString(instanceC.getClass().getAnnotations()));
  }

  /**
   * 运行结果:
   已使用的@Inherited注解:[@com.zejian.annotationdemo.DocumentA()]
   没有使用的@Inherited注解:[]
   */
}

package com.zejian.annotationdemo;

import java.lang.annotation.Annotation;
import java.util.Arrays;

/**
 * Created by zejian on 2017/5/20.

 */
@DocumentA
class A{ }

//继承了A类
@DocumentB
public class DocumentDemo extends A{

  public static void main(String... args){

    Class<?> clazz = DocumentDemo.class;
    //根据指定注解类型获取该注解
    DocumentA documentA=clazz.getAnnotation(DocumentA.class);
    System.out.println("A:"+documentA);

    //获取该元素上的所有注解，包含从父类继承
    Annotation[] an= clazz.getAnnotations();
    System.out.println("an:"+ Arrays.toString(an));
    //获取该元素上的所有注解，但不包含继承！
    Annotation[] an2=clazz.getDeclaredAnnotations();
    System.out.println("an2:"+ Arrays.toString(an2));

    //判断注解DocumentA是否在该元素上
    boolean b=clazz.isAnnotationPresent(DocumentA.class);
    System.out.println("b:"+b);

    /**
     * 执行结果:
     A:@com.zejian.annotationdemo.DocumentA()
     an:[@com.zejian.annotationdemo.DocumentA(), @com.zejian.annotationdemo.DocumentB()]
     an2:@com.zejian.annotationdemo.DocumentB()
     b:true
     */
  }
}

/**
 * Created by wuzejian on 2017/5/18.
 * 表注解
 */
@Target(ElementType.TYPE)//只能应用于类上
@Retention(RetentionPolicy.RUNTIME)//保存到运行时
public @interface DBTable {
  String name() default "";
}


/**
 * Created by wuzejian on 2017/5/18.
 * 注解Integer类型的字段
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface SQLInteger {
  //该字段对应数据库表列名
  String name() default "";
  //嵌套注解
  Constraints constraint() default @Constraints;
}


/**
 * Created by wuzejian on 2017/5/18.
 * 注解String类型的字段
 */
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface SQLString {

  //对应数据库表的列名
  String name() default "";

  //列类型分配的长度，如varchar(30)的30
  int value() default 0;

  Constraints constraint() default @Constraints;
}


/**
 * Created by wuzejian on 2017/5/18.
 * 约束注解
 */

@Target(ElementType.FIELD)//只能应用在字段上
@Retention(RetentionPolicy.RUNTIME)
public @interface Constraints {
  //判断是否作为主键约束
  boolean primaryKey() default false;
  //判断是否允许为null
  boolean allowNull() default false;
  //判断是否唯一
  boolean unique() default false;
}

/**
 * Created by wuzejian on 2017/5/18.
 * 数据库表Member对应实例类bean
 */
@DBTable(name = "MEMBER")
public class Member {
  //主键ID
  @SQLString(name = "ID",value = 50, constraint = @Constraints(primaryKey = true))
  private String id;

  @SQLString(name = "NAME" , value = 30)
  private String name;

  @SQLInteger(name = "AGE")
  private int age;

  @SQLString(name = "DESCRIPTION" ,value = 150 , constraint = @Constraints(allowNull = true))
  private String description;//个人描述

  //省略set get.....
}

package com.zejian.annotationdemo;
import java.lang.annotation.Annotation;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

/**
 * Created by zejian on 2017/5/13.
 * 运行时注解处理器，构造表创建语句
 */
public class TableCreator {

 public static String createTableSql(String className) throws ClassNotFoundException {
  Class<?> cl = Class.forName(className);
  DBTable dbTable = cl.getAnnotation(DBTable.class);
  //如果没有表注解，直接返回
  if(dbTable == null) {
   System.out.println(
       "No DBTable annotations in class " + className);
   return null;
  }
  String tableName = dbTable.name();
  // If the name is empty, use the Class name:
  if(tableName.length() < 1)
   tableName = cl.getName().toUpperCase();
  List<String> columnDefs = new ArrayList<String>();
  //通过Class类API获取到所有成员字段
  for(Field field : cl.getDeclaredFields()) {
   String columnName = null;
   //获取字段上的注解
   Annotation[] anns = field.getDeclaredAnnotations();
   if(anns.length < 1)
    continue; // Not a db table column

   //判断注解类型
   if(anns[0] instanceof SQLInteger) {
    SQLInteger sInt = (SQLInteger) anns[0];
    //获取字段对应列名称，如果没有就是使用字段名称替代
    if(sInt.name().length() < 1)
     columnName = field.getName().toUpperCase();
    else
     columnName = sInt.name();
    //构建语句
    columnDefs.add(columnName + " INT" +
        getConstraints(sInt.constraint()));
   }
   //判断String类型
   if(anns[0] instanceof SQLString) {
    SQLString sString = (SQLString) anns[0];
    // Use field name if name not specified.
    if(sString.name().length() < 1)
     columnName = field.getName().toUpperCase();
    else
     columnName = sString.name();
    columnDefs.add(columnName + " VARCHAR(" +
        sString.value() + ")" +
        getConstraints(sString.constraint()));
   }


  }
  //数据库表构建语句
  StringBuilder createCommand = new StringBuilder(
      "CREATE TABLE " + tableName + "(");
  for(String columnDef : columnDefs)
   createCommand.append("\n  " + columnDef + ",");

  // Remove trailing comma
  String tableCreate = createCommand.substring(
      0, createCommand.length() - 1) + ");";
  return tableCreate;
 }


  /**
   * 判断该字段是否有其他约束
   * @param con
   * @return
   */
 private static String getConstraints(Constraints con) {
  String constraints = "";
  if(!con.allowNull())
   constraints += " NOT NULL";
  if(con.primaryKey())
   constraints += " PRIMARY KEY";
  if(con.unique())
   constraints += " UNIQUE";
  return constraints;
 }

 public static void main(String[] args) throws Exception {
  String[] arg={"com.zejian.annotationdemo.Member"};
  for(String className : arg) {
   System.out.println("Table Creation SQL for " +
       className + " is :\n" + createTableSql(className));
  }

  /**
   * 输出结果：
   Table Creation SQL for com.zejian.annotationdemo.Member is :
   CREATE TABLE MEMBER(
   ID VARCHAR(50) NOT NULL PRIMARY KEY,
   NAME VARCHAR(30) NOT NULL,
   AGE INT NOT NULL,
   DESCRIPTION VARCHAR(150)
   );
   */
 }
}

//Java8前无法这样使用
@FilterPath("/web/update")
@FilterPath("/web/add")
public class A {}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface FilterPath {
  String [] value();
}

//使用
@FilterPath({"/update","/add"})
public class A { }

package com.zejian.annotationdemo;

import java.lang.annotation.*;

/**
 * Created by zejian on 2017/5/20.
 */
//使用Java8新增@Repeatable原注解
@Target({ElementType.TYPE,ElementType.FIELD,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Repeatable(FilterPaths.class)//参数指明接收的注解class
public @interface FilterPath {
  String value();
}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface FilterPaths {
  FilterPath[] value();
}

//使用案例
@FilterPath("/web/update")
@FilterPath("/web/add")
@FilterPath("/web/delete")
class AA{ }

/**
 * Created by zejian on 2017/5/20.
 */
//使用Java8新增@Repeatable原注解
@Target({ElementType.TYPE,ElementType.FIELD,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Repeatable(FilterPaths.class)
public @interface FilterPath {
  String value();
}


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface FilterPaths {
  FilterPath[] value();
}

@FilterPath("/web/list")
class CC { }

//使用案例
@FilterPath("/web/update")
@FilterPath("/web/add")
@FilterPath("/web/delete")
class AA extends CC{
  public static void main(String[] args) {

    Class<?> clazz = AA.class;
    //通过getAnnotationsByType方法获取所有重复注解
    FilterPath[] annotationsByType = clazz.getAnnotationsByType(FilterPath.class);
    FilterPath[] annotationsByType2 = clazz.getDeclaredAnnotationsByType(FilterPath.class);
    if (annotationsByType != null) {
      for (FilterPath filter : annotationsByType) {
        System.out.println("1:"+filter.value());
      }
    }

    System.out.println("-----------------");

    if (annotationsByType2 != null) {
      for (FilterPath filter : annotationsByType2) {
        System.out.println("2:"+filter.value());
      }
    }


    System.out.println("使用getAnnotation的结果:"+clazz.getAnnotation(FilterPath.class));


    /**
     * 执行结果(当前类拥有该注解FilterPath,则不会从CC父类寻找)
     1:/web/update
     1:/web/add
     1:/web/delete
     -----------------
     2:/web/update
     2:/web/add
     2:/web/delete
     使用getAnnotation的结果:null
     */
  }
}

/**
 * Created by zejian on 2017/5/20.
 */
//使用Java8新增@Repeatable原注解
@Target({ElementType.TYPE,ElementType.FIELD,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited //添加可继承元注解
@Repeatable(FilterPaths.class)
public @interface FilterPath {
  String value();
}


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Inherited //添加可继承元注解
@interface FilterPaths {
  FilterPath[] value();
}

@FilterPath("/web/list")
@FilterPath("/web/getList")
class CC { }

//AA上不使用@FilterPath注解,getAnnotationsByType将会从父类查询
class AA extends CC{
  public static void main(String[] args) {

    Class<?> clazz = AA.class;
    //通过getAnnotationsByType方法获取所有重复注解
    FilterPath[] annotationsByType = clazz.getAnnotationsByType(FilterPath.class);
    FilterPath[] annotationsByType2 = clazz.getDeclaredAnnotationsByType(FilterPath.class);
    if (annotationsByType != null) {
      for (FilterPath filter : annotationsByType) {
        System.out.println("1:"+filter.value());
      }
    }

    System.out.println("-----------------");

    if (annotationsByType2 != null) {
      for (FilterPath filter : annotationsByType2) {
        System.out.println("2:"+filter.value());
      }
    }


    System.out.println("使用getAnnotation的结果:"+clazz.getAnnotation(FilterPath.class));


    /**
     * 执行结果(当前类没有@FilterPath,getAnnotationsByType方法从CC父类寻找)
     1:/web/list
     1:/web/getList
     -----------------
     使用getAnnotation的结果:null
     */
  }
}

//接口默认实现方法
default <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass) {
//先调用getDeclaredAnnotationsByType方法
T[] result = getDeclaredAnnotationsByType(annotationClass);

//判断当前类获取到的注解数组是否为0
if (result.length == 0 && this instanceof Class && 
//判断定义注解上是否使用了@Inherited元注解 
 AnnotationType.getInstance(annotationClass).isInherited()) { // Inheritable
    //从父类获取
    Class<?> superClass = ((Class<?>) this).getSuperclass();
  if (superClass != null) {
   result = superClass.getAnnotationsByType(annotationClass);
    }
  }

  return result;
}

//TYPE_PARAMETER 标注在类型参数上
class D<@Parameter T> { }

//TYPE_USE则可以用于标注任意类型(不包括class)
//用于父类或者接口
class Image implements @Rectangular Shape { }

//用于构造函数
new @Path String("/usr/bin")

//用于强制转换和instanceof检查,注意这些注解中用于外部工具，它们不会对类型转换或者instanceof的检查行为带来任何影响。
String path=(@Path String)input;
if(input instanceof @Path String)

//用于指定异常
public Person read() throws @Localized IOException.

//用于通配符绑定
List<@ReadOnly ? extends Person>
List<? extends @ReadOnly Person>

@NotNull String.class //非法，不能标注class
import java.lang.@NotNull String //非法，不能标注import