Java Annotation(Java 注解)的实现代码

如果你想知道java annotation是什么？你可以先看看：“http://www.infoq.com/articles/annotation-hammer”

下面是我做的一个demo：

项目结构：

运行效果：

====================================================

代码部分：

注：很多人会考虑这个问题，“这样做的目的是什么？我们可以做一个配置文件（xml，properties等），不是比这个跟方便...或者说

直接把我们的配置信息写入程序...这样也不会去解析我们写的注释..”

但是annotation和xml，properties等配置文件的优缺点是什么呢..

个人观点：写注释的时候，比较方便...可以提高开发的效率.有用到注释的框架，如：hibernate，struts，spring等

回到原话题，“这样做的目的是什么？“---这里只是做一个demo，让大家知道annotation是怎么一回事儿....在很多我们开发的

过程中，很少用到我们自己定义的注释(annotation),如果真的用到了，那么这篇blog也许就有帮助了..^_^

====================================================

/java_annotation/src/com/b510/hongten/annotation/jdbcannotation.java

/**
  *
  */
 package com.b510.hongten.annotation;

 import java.lang.annotation.documented;
 import java.lang.annotation.elementtype;
 import java.lang.annotation.retention;
 import java.lang.annotation.retentionpolicy;
 import java.lang.annotation.target;

 /**
  * jdbc annotation
  *
  * @author hongten
  * @date 2013-4-10
  */
 @documented
 @retention(retentionpolicy.runtime)
 @target(elementtype.type)
 public @interface jdbcannotation {

     string driver() default "com.mysql.jdbc.driver";

     string dbname() default "";

     string encoding() default "utf-8";

     string port() default "3306";

     string host() default "localhost";

     string username() default "root";

     string password() default "";

 }

/java_annotation/src/com/b510/hongten/jdbc/jdbcutil.java

/**
  *
  */
 package com.b510.hongten.jdbc;

 import com.b510.hongten.annotation.jdbcannotation;

 /**
  * @author hongten
  * @date 2013-4-12
  */
 @jdbcannotation(dbname = "db_lucene", port = "3306", host = "192.168.0.119", username = "root", password = "root")
 public class jdbcutil {

     private static string driver;
     private static string dbname;
     private static string encoding;
     private static string port;
     private static string host;
     private static string passwrod;
     private static string username;
     private static string url;

     public void checkinterceptor(class<?> cl) throws exception {
         boolean flag = cl.isannotationpresent(jdbcannotation.class);
         if (flag) {
             jdbcannotation jdbcannotation = cl.getannotation(jdbcannotation.class);
             driver = jdbcannotation.driver();
             dbname = jdbcannotation.dbname();
             encoding = jdbcannotation.encoding();
             port = jdbcannotation.port();
             host = jdbcannotation.host();
             username = jdbcannotation.username();
             passwrod = jdbcannotation.password();
             url = "jdbc:mysql://" + host + ":" + port + "/" + dbname + "?characterencoding=" + encoding;
             system.out.println("jdbcutil加载注释完成...");
         }
     }

     public jdbcutil() {
         try {
             checkinterceptor(jdbcutil.class);
         } catch (exception e) {
             e.printstacktrace();
         }
     }

     public static string getdriver() {
         return driver;
     }

     public static void setdriver(string driver) {
         jdbcutil.driver = driver;
     }

     public static string getdbname() {
         return dbname;
     }

     public static void setdbname(string dbname) {
         jdbcutil.dbname = dbname;
     }

     public static string getencoding() {
         return encoding;
     }

     public static void setencoding(string encoding) {
         jdbcutil.encoding = encoding;
     }

     public static string getport() {
         return port;
     }

     public static void setport(string port) {
         jdbcutil.port = port;
     }

     public static string gethost() {
         return host;
     }

     public static void sethost(string host) {
         jdbcutil.host = host;
     }

     public static string getpasswrod() {
         return passwrod;
     }

     public static void setpasswrod(string passwrod) {
         jdbcutil.passwrod = passwrod;
     }

     public static string getusername() {
         return username;
     }

     public static void setusername(string username) {
         jdbcutil.username = username;
     }

     public static string geturl() {
         return url;
     }

     public static void seturl(string url) {
         jdbcutil.url = url;
     }

    
 }

/java_annotation/src/com/b510/hongten/jdbc/jdbctest.java

/**
  *
  */
 package com.b510.hongten.jdbc;

 import java.sql.connection;
 import java.sql.drivermanager;
 import java.sql.preparedstatement;
 import java.sql.resultset;
 import java.sql.sqlexception;

 /**
  *
  * @author hongten</br>
  * @date 2012-7-16
  *
  */
 public class jdbctest {
     @suppresswarnings("static-access")
     public static void main(string[] args) {
         jdbcutil jdbcutil = new jdbcutil();
         string sql = "select * from mymails";
         try {
             class.forname(jdbcutil.getdriver());
             connection conn = drivermanager.getconnection(jdbcutil.geturl(), jdbcutil.getusername(), jdbcutil.getpasswrod());
             preparedstatement ps = conn.preparestatement(sql);
             resultset rs = ps.executequery();
             while (rs.next()) {
                 system.out.println("id : " + rs.getint(1) + " name : " + rs.getstring(2) + " mail : " + rs.getstring(3));
             }
             // 关闭记录集
             if (rs != null) {
                 try {
                     rs.close();
                 } catch (sqlexception e) {
                     e.printstacktrace();
                 }
             }

             // 关闭声明
             if (ps != null) {
                 try {
                     ps.close();
                 } catch (sqlexception e) {
                     e.printstacktrace();
                 }
             }

             // 关闭链接对象
             if (conn != null) {
                 try {
                     conn.close();
                 } catch (sqlexception e) {
                     e.printstacktrace();
                 }
             }
         } catch (exception e) {
             e.printstacktrace();
         }
     }

 }