常用公共类代码一之数据库的连接

在项目中，我们经常会写到一些公共的代码，来让开发人员调用，减少代码重复，下面，我就将一些常用到的公共类贴出来和大家分享！！

一、数据库的连接，常用的方式有直接将那些要连接的参数放到java类中、将连接参数放到Properties文件中或者放到XML文件中，下面一一为大家描述

1、直接连接：

        普通的配置方式
	public static Connection getConnection(){
		Connection conn=null;
		try {
			Class.forName("com.mysql.jdbc.Driver");
			String url="jdbc:mysql://127.0.0.1:3306/xinyuandb";
			String username="root";
			String password="123456";
			conn=DriverManager.getConnection(url, username, password);
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return conn;
	}

2、通过Properties文件创建连接，好处，很灵活，不用在代码里面进行更改

创建jdbc.properties文件

driver=com.mysql.jdbc.Driver
url=jdbc\:mysql\://127.0.0.1\:3306/xinyuandb
username=root
password=123456

        从properties文件中读取
	public static Connection getConnection(){
		Connection conn=null;
		Properties p=new Properties();
		try {
			//从当前线程加载
			p.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("jdbc.properties"));
			Class.forName(p.getProperty("driver"));
			conn=DriverManager.getConnection(p.getProperty("url"), p.getProperty("username"), p.getProperty("password"));
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		return conn;
	}

3、通过XML文件读取
  创建jdbc.xml文件
<?xml version="1.0" encoding="UTF-8"?>
<config>
 <jdbc-config>
  <driver>com.mysql.jdbc.Driver</driver>
  <url>jdbc:mysql://127.0.0.1:3306/xinyuandb</url>
  <username>root</username>
  <password>123456</password>
 </jdbc-config>
</config>
创建javaBean类
package com.common.db;

public class JdbcBean {
 private String driver;
 private String url;
 private String username;
 private String password;
 public String getDriver() {
  return driver;
 }
 public void setDriver(String driver) {
  this.driver = driver;
 }
 public String getUrl() {
  return url;
 }
 public void setUrl(String url) {
  this.url = url;
 }
 public String getUsername() {
  return username;
 }
 public void setUsername(String username) {
  this.username = username;
 }
 public String getPassword() {
  return password;
 }
 public void setPassword(String password) {
  this.password = password;
 }
}

创建XML解析类
package com.common.db;

import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;

public class XmlConfigReader {
	private static XmlConfigReader instance;
	private JdbcBean bean=null;
	//调用构造函数进行XML文件解析
	private XmlConfigReader(){
		SAXReader reader=new SAXReader();
		try {
			Document doc=reader.read(Thread.currentThread().getContextClassLoader().getResourceAsStream("jdbc.xml"));
			Element root=doc.getRootElement();
			Element first=root.element("jdbc-config");
			String driver=first.element("driver").getText();
			String url=first.element("url").getText();
			String username=first.element("username").getText();
			String password=first.element("password").getText();
			bean=new JdbcBean();
			bean.setDriver(driver);
			bean.setUrl(url);
			bean.setUsername(username);
			bean.setPassword(password);
		} catch (DocumentException e) {
			e.printStackTrace();
		}
	}
	
	public synchronized static XmlConfigReader getInstance(){
		if(instance==null){
			instance=new XmlConfigReader();
		}
		return instance;
	}
	
	public JdbcBean getJdbeanBean(){
		return bean;
	}

}


// 从XML文件中读取配置取得同一Connection

// static Connection conn=null;

// static{

//  JdbcBean jdbc=XmlConfigReader.getInstance().getJdbeanBean();

//  try {

//   Class.forName(jdbc.getDriver());

//   conn=DriverManager.getConnection(jdbc.getUrl(), jdbc.getUsername(),jdbc.getPassword());

//  } catch (ClassNotFoundException e) {

//   e.printStackTrace();

//  } catch (SQLException e) {

//   e.printStackTrace();

//  }

// }


 //从XML文件中读取配置

 public static Connection getConnection(){

  Connection conn=null;

  JdbcBean jdbc=XmlConfigReader.getInstance().getJdbeanBean();

  try {

   Class.forName(jdbc.getDriver());

   conn=DriverManager.getConnection(jdbc.getUrl(), jdbc.getUsername(),jdbc.getPassword());

  } catch (ClassNotFoundException e) {

   e.printStackTrace();

  } catch (SQLException e) {

   e.printStackTrace();

  }

  return conn;

 }


有时候我们想取得Connection的单实例，又不会影响到其安全性，我们可以通过线程ThreadLocal来对Connection进行管理：

package com.common.db;

import java.sql.Connection;

/**
 * 线程管理
 * @author Administrator
 *
 */
public class ConnectionManager {
	//使用线程变量对Connection进行管理
	private static ThreadLocal<Connection> local=new ThreadLocal<Connection>();
	
	public static Connection getConnection(){
		Connection conn=local.get();
		if(conn==null){
			conn=DbUtil.getConnection();
			local.set(conn);
		}
		return conn;
	}
	public static void main(String[] args) {
		Connection conn1=ConnectionManager.getConnection();
		Connection conn2=ConnectionManager.getConnection();
		Connection conn3=DbUtil.getConnection();
		Connection conn4=DbUtil.getConnection();
		System.out.println(conn1==conn2);//true
		System.out.println(conn3==conn4);//false
	}
}


这样，数据库操作的公共类基本上实现了，大家在项目中就可以进行调用了，当然，还有一些基本的流的关闭和事物的处理，代码如下：
       public static void close(Connection conn) {
		if (conn != null) {
			try {
				conn.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
	
	public static void close(Statement pstmt) {
		if (pstmt != null) {
			try {
				pstmt.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
	
	public static void close(ResultSet rs ) {
		if (rs != null) {
			try {
				rs.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
	}
	
	public static void beginTransaction(Connection conn) {
		try {
			if (conn != null) {
				if (conn.getAutoCommit()) {
					conn.setAutoCommit(false); //手动提交
				}
			}
		}catch(SQLException e) {}
	}
				
	public static void commitTransaction(Connection conn) {
		try {
			if (conn != null) {
				if (!conn.getAutoCommit()) {
					conn.commit();
				}
			}
		}catch(SQLException e) {}
	}
	
	public static void rollbackTransaction(Connection conn) {
		try {
			if (conn != null) {
				if (!conn.getAutoCommit()) {
					conn.rollback();
				}
			}
		}catch(SQLException e) {}
	}
	
	public static void resetConnection(Connection conn) {
		try {
			if (conn != null) {
				if (conn.getAutoCommit()) {
					conn.setAutoCommit(false);
				}else {
					conn.setAutoCommit(true);
				}
			}
		}catch(SQLException e) {}
	}