注解分类

一、运行机制划分:

源码注解
编译时注解 (1.内的注解都是)
只在编译器上起作用
运行时注解
运行阶段起作用,影响运行逻辑,例如@Autowired

二、按照来源划分:

1.jdk自带注解

@Override 复写父类,接口方法
@Depreted 标记过时
@SuppressWarning(“deprecation”) 忽略警告

2.java第三方注解

Spring注解
参考文章作者:陈袁

SpringBoot注解
作者 tanwei81 博客园

3.自定义注解

//使用@interface定义注解
// CONSTRUCTOR:构造方法声明  FIELD:字段 LOCAL_VARIABLE:局部变量 
// METHOD:方法 PACKAGE:包  PARAMETER:参数 TYPE:接口.类
@Target({ElementType.CONSTRUCTOR, ElementType.METHOD,ElementType.ANNOTATION_TYPE})
// 存在范围 source:编译时忽略掉
@Retention(RetentionPolicy.RUNTIME)
@Inherited//允许子类(子注解)继承,对接口继承没有作用[extends]
@Documented//生成javadoc会包含注解信息 
public @interface Description{
    //成员变量以无参无异常的方式声明 
    //成员类型受限于8种基本类型和String,Class,Annotation,Enumeration
    String desc();
    String author();
    int age() default 18;
}
//只有一个成员变量时,名称必须为value(),使用时可忽略'='或成员名
public @interface Description{
    String value();
}
//没有成员的注解成为标识注解
public @interface Description{
}

8种基本类型: byte,short,int,long,float,double,char,boolean

元注解: 给注解进行注解

// CONSTRUCTOR:构造方法声明  FIELD:字段 LOCAL_VARIABLE:局部变量 
// METHOD:方法 PACKAGE:包  PARAMETER:参数 TYPE:接口.类
@Target({ElementType.CONSTRUCTOR, ElementType.METHOD,ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited//注解会被子类继承
public @interface Autowired {
    /**
     * Declares whether the annotated dependency is required.
     * <p>Defaults to {@code true}.
     */
    boolean required() default true;
}

java注解 - 图1

解析注释

try{
    //1.找到类上的注解,反射加载类
    Class c = Class.forName("com.zjy.entity.Child");
    //2.找到类上面的注解
    boolean isExist = c.isAnnotationPresent(Description.class);
    if(isExist){
        //3.存在注解实例,取出
        Description d = (Description)c.getAnnotation(Description.class);
        System.out.println(d.value());
    }
    //1.找到方法上的注解
    Method[] ms = c.getMethods();
    for(Method m : ms){
        boolean isExist = m.isAnnotationPresent(Description.class);
        if(isExist){
            //2.存在注解实例,取出
            Description d = (Description)c.getAnnotation(Description.class);
            System.out.println(d.value());
        }
    }
    //1.找到方法所有注解
    for(Method m : ms){
        Annotation[] as = m.getAnnotations();
        for(Annotation a: as){
            if(a instanceod Description){
                Description d = (Description)a;
                System.out.println(d.value());
            }
        } 
    }
}catch(ClassNotFoundException e){
    logger.error("",e);
}

实例

import org.springframework.stereotype.Component;
import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component//作为左键能被spring扫描到
public @interface SQLFileAnnotation {
    String SQLFileName();
}

主方法内扫描注解

    public static void scannerBeans(){
        //扫描SQL文件注解
        String[] sqlFiles = applicationContext.getBeanNamesForAnnotation(SQLFileAnnotation.class);
        List<String> sqlFileNameList = new ArrayList<>();
        for(String string:sqlFiles){
            Object sqlFile = applicationContext.getBean(string);
            String sqlFileName = sqlFile.getClass().getAnnotation(SQLFileAnnotation.class).SQLFileName();
            sqlFileNameList.add(sqlFileName);
        }
        executeSql(sqlFileNameList);
    }
    private static void executeSql(List<String> sqlFileNameList){
        Collections.sort(sqlFileNameList, new Comparator<String>() {
            @Override
            public int compare(String o1, String o2) {
                if(o1.contains("-")){
                    o1 = o1.substring(o1.indexOf("-") + 1,o1.length());
                }
                if(o2.contains("-")){
                    o2 = o2.substring(o2.indexOf("-") + 1,o2.length());
                }
                return o1.compareTo(o2);
            }
        });
        for(String name : sqlFileNameList){
            String importedDBs = getImportedDBs();
            if(importedDBs.contains(name)){
                logger.debug("数据库已导入，不再重复导入！！");
                continue;
            }
            boolean isSuccess = false;
            try {
                String content = "";
                try {
                    content = IOUtils.toString(new FileInputStream(PathUtil.getPath(PathUtil.PathType.CONFIG)+ "sqlitemanagerTool.sql"),"utf-8");
                } catch (IOException e) {
                    e.printStackTrace();
                }
                isSuccess = JdbcUtil.getInstance().insertSqlArray(content.split("#970126#"));
            } catch (Exception e) {
                e.printStackTrace();
            }
            if(isSuccess){
                updateImportedDB(importedDBs + "\r\n" + name);
            }
        }
    }
    private static String getImportedDBs(){
        StringBuilder importedDB=new StringBuilder();
        try {
            File file =new File(PathUtil.getPath(PathUtil.PathType.CONFIG) + "dbImport.txt");
            if(!file.exists()){
                file.createNewFile();
            }
            FileInputStream in=new FileInputStream(file);
            byte[] b=new byte[1024];
            int i;
            while((i=in.read(b))>0){
                importedDB.append(new String(b,0,i));
            }
            in.close();
        }catch (Exception e){
            e.printStackTrace();
        }
        return importedDB.toString();
    }
    private static void updateImportedDB(String string){
        try {
            File file =new File(PathUtil.getPath(PathUtil.PathType.CONFIG) + "dbImport.txt");
            FileOutputStream out =new FileOutputStream(file);
            byte[] newb = string.getBytes();
            out.write(newb);
            out.close();
        }catch (Exception e){
            e.printStackTrace();
        }
    }