Java Annotation(Java 注解)的实现代码

      2020-03-18 02:05      JAVA编程
本篇文章介绍了,Java Annotation(Java 注解)的实现代码。需要的朋友参考下

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
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();
}
}

}