jdbc數據庫連接mysql

import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public class JDBC {
 
 private static JDBC jdbc;
 
 // 雙重檢查
 public static JDBC getInstance() {
  if (jdbc == null) {
   synchronized(JDBC.class) {
    if (jdbc == null) {
     jdbc = new JDBC();
    }
   }
  }
  return jdbc;
 }
 
 // 同步方法實現
 public static synchronized JDBC getInstance2() {
  if (jdbc == null) {
   jdbc = new JDBC();
  }
  return jdbc;
 }
 
 public static Properties props = new Properties();
 
 private static final Log log = LogFactory.getLog(JDBC.class);
 
 static {
  try {
   props.load(JDBC.class.getClassLoader()
     .getResourceAsStream("jdbc_mysql.properties"));
   Class.forName(props.getProperty("driver"));
  } catch (IOException e) {
   e.printStackTrace();
  } catch (ClassNotFoundException e) {
   e.printStackTrace();
  }
  
 }
 
 /**
  *
  * @return 連接
  */
 public static Connection getConnection() {
  
  Connection conn = null;
  String url = props.getProperty("url");
  String user = props.getProperty("user");
  String password = props.getProperty("password");
  try {
   conn = DriverManager.getConnection(url, user, password);
  } catch (SQLException e) {
   log.error("建立連接失敗");
  }
  return conn;
 } 
 
 /**
  * 釋放資源
  *
  * @param rs 結果集
  * @param stmt 執行語句
  * @param conn 連接
  */
 public static void freeResource(ResultSet rs, Statement stmt, Connection conn) {
  if (rs != null) {
   try {
    rs.close();
   } catch (SQLException e) {
    log.error("關閉數據集失敗");
   }
   rs = null;
  }
  
  if (stmt != null) {
   try {
    stmt.close();
   } catch (SQLException e) {
    log.error("關閉執行語句失敗");
   }
   rs = null;
  }
  
  if (conn != null) {
   try {
    conn.close();
   } catch (SQLException e) {
    log.error("關閉連接失敗");
   }
   conn = null;
  }
 }
 
 /**
  * 釋放資源
  *
  * @param stmt 執行語句
  * @param conn 連接
  */
 public static void freeResource(Statement stmt, Connection conn) {
  freeResource(null, stmt, conn);
 }
 
 /**
  * 釋放資源
  *
  * @param conn 連接
  */
 public static void freeResource(Connection conn) {
  freeResource(null, null, conn);
 }
 
 public static void main(String[] args) {
  Connection conn = null;
  Statement stmt = null;
  ResultSet rs = null;
  conn = getConnection();
  try {
   stmt = conn.createStatement();
   rs = stmt.executeQuery("select * from t");
   while (rs.next()) {
    System.out.println(rs.getObject("t") + "/t");
   }
  } catch (SQLException e) {
   e.printStackTrace();
  } finally {
   freeResource(rs, stmt, conn);
  }
 }

}

 

jdbc_mysql.properties

 

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/test
user=root
password=root
characterEncoding=gb2312

 

 

log4j.properties

 

# For JBoss: Avoid to setup Log4J outside $JBOSS_HOME/server/default/deploy/log4j.xml!
# For all other servers: Comment out the Log4J listener in web.xml to activate Log4J.
log4j.rootLogger=INFO, stdout, logfile

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - %m%n

log4j.appender.logfile=org.apache.log4j.RollingFileAppender
log4j.appender.logfile.File=d:/out.log
log4j.appender.logfile.MaxFileSize=512KB
# Keep three backup files.
log4j.appender.logfile.MaxBackupIndex=3
# Pattern to output: date priority [category] - message
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=%d %p [%c] - %m%n