Java Annotation(Java 注解)的实现代码

2019-11-26 16:09:27

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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..^_^

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

复制代码代码如下:

/**
  * 
  */
 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

复制代码代码如下:

/**
  * 
  */
 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

复制代码代码如下:

/**
  * 
  */
 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();
         }
     }

 }