Java Annotation(Java 注解)

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：

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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

/**
 * 
 */
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();
        }
    }

}