少年阿賓

那些青春的歲月

:: 管理

500 Posts :: 0 Stories :: 135 Comments :: 0 Trackbacks

主鍵與唯一索引的區別：
主鍵是一種約束，唯一索引是一種索引，兩者在本質上是不同的。

主鍵創建后一定包含一個唯一性索引，唯一性索引并不一定就是主鍵。

唯一性索引列允許空值，而主鍵列不允許為空值。

主鍵列在創建時，已經默認為空值 + 唯一索引了。

主鍵可以被其他表引用為外鍵，而唯一索引不能。

一個表最多只能創建一個主鍵，但可以創建多個唯一索引。

主鍵更適合那些不容易更改的唯一標識，如自動遞增列、身份證號等。

很簡單，主鍵約束不能重復，不可為空（NULL)。
唯一性約束，不能重復，可為空(NULL)，但是只能由一個NULL。

posted @ 2012-09-04 22:56 abin 閱讀(459) | 評論 (0) | 編輯收藏

Java 創建數據庫連接池(二)

package com.abin.lee.collection.pool;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class ConnectionPool {
private List<Connection> pool;
private static final String Url = "jdbc:oracle:thin:@localhost:1521:XE";
private static final String USERNAME = "abing";
private static final String PASSWORD = "abing";
private static final String DRIVER = "oracle.jdbc.driver.OracleDriver";
private int poolSize = 10;
private static volatile ConnectionPool instance = null;

private ConnectionPool() {
init();
}

public void init() {
pool = new ArrayList<Connection>(poolSize);
addConnection();
}

public synchronized void release(Connection conn) {
pool.add(conn);
}

public synchronized void closePool() {
  for (int i = 0; i < pool.size(); i++) {
   try {
    ((Connection) pool.get(i)).close();
   } catch (SQLException e) {
    e.printStackTrace();
   }
   pool.remove(i);
  }
}

public static ConnectionPool getInstance() {
  if (null == instance) {
   synchronized (ConnectionPool.class) {
    if (null == instance) {
     return new ConnectionPool();
    }
   }
  }
  return instance;
}

public synchronized Connection getConnection() {
  if (pool.size() > 0) {
   Connection conn = pool.get(0);
   if(conn!=null){
    System.out.println("Connection Pool Create Success");
   }
   pool.remove(conn);
   return conn;
  }else{
   return null;
  }
}

public void addConnection() {
  Connection conn = null;
  for (int i = 0; i < poolSize; i++) {
   try {
    Class.forName(DRIVER);
    conn = DriverManager.getConnection(Url, USERNAME, PASSWORD);
    pool.add(conn);
   } catch (Exception e) {
    e.printStackTrace();
   }

}
}

}

測試代碼：

package com.abin.lee.collection.pool;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import com.abin.lee.collection.threadlocal.UserBean;

public class TestConnectionPool {

public static List<UserBean> findAll(){
  Connection conn=null;
  PreparedStatement ps=null;
  ResultSet rs=null;
  String sql="select * from userbean order by id desc";
  List<UserBean> list=new ArrayList<UserBean>();
  UserBean user=null;
  try {
   conn=ConnectionPool.getInstance().getConnection();
   ps=conn.prepareStatement(sql);
   rs=ps.executeQuery();
   while (rs.next()&&rs!=null) {
    user=new UserBean();
    user.setId(rs.getString("id"));
    user.setUsername(rs.getString("username"));
    user.setPassword(rs.getString("password"));
    list.add(user);
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
  return list;
}
public static void main(String[] args) {
  List<UserBean> list=findAll();
  for(UserBean lst:list){
   System.out.println("id="+lst.getId());
   System.out.println("username="+lst.getUsername());
   System.out.println("id="+lst.getPassword());
  }
}

}

posted @ 2012-09-04 00:20 abin 閱讀(450) | 評論 (0) | 編輯收藏

Java 創建數據庫連接池(一)

package com.abin.lee.collection.pool;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.LinkedList;
import java.util.List;

public class ConnectionManage {
private static List<Connection> pool=new LinkedList<Connection>();;
private static final String Url = "jdbc:oracle:thin:@localhost:1521:XE";
private static final String USERNAME = "abing";
private static final String PASSWORD = "abing";
private static final String DRIVER = "oracle.jdbc.driver.OracleDriver";
private static int initCount = 5;
private static int maxCount = 10;
private static int currentCount = 5;
private static volatile ConnectionManage instance = null;
private ConnectionManage(){
  init();
}
public static ConnectionManage getInstance(){
  if(null == instance){
   synchronized (ConnectionManage.class) {
    if(null == instance){
     return new ConnectionManage();
    }
   }
  }
  return instance;
}
public void init(){
  addConnection();
}
public static Connection createConnection() throws ClassNotFoundException {
  Connection conn=null;
  try {
   Class.forName(DRIVER);
   conn=DriverManager.getConnection(Url, USERNAME, PASSWORD);
  } catch (SQLException e) {
   e.printStackTrace();
  }
  return conn;
}
public static void addConnection(){
  for(int i=0;i<initCount;i++){
   try {
    pool.add(createConnection());
   } catch (ClassNotFoundException e) {
    e.printStackTrace();
   }
  }
}

public static void release(Connection conn){
  pool.add(conn);
}
public static Connection getConnection() throws SQLException, ClassNotFoundException{
  synchronized (pool) {
   if(pool.size()>0){
    System.out.println("Current Connection size is:"+pool.size());
    return pool.get(0);
   }else if(currentCount<maxCount){
    Class.forName(DRIVER);
    Connection conn=createConnection();
    pool.add(conn);
    currentCount++;
    return conn;
   }else{
    throw new SQLException("Current Connection is Zero");
   }
  }
}

}

測試代碼：

package com.abin.lee.collection.pool;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import com.abin.lee.collection.threadlocal.UserBean;

public class TestConnectionPool {

public static List<UserBean> findAll(){
  Connection conn=null;
  PreparedStatement ps=null;
  ResultSet rs=null;
  String sql="select * from userbean order by id desc";
  List<UserBean> list=new ArrayList<UserBean>();
  UserBean user=null;
  try {
   conn=ConnectionManage.getInstance().getConnection();
   ps=conn.prepareStatement(sql);
   rs=ps.executeQuery();
   while (rs.next()&&rs!=null) {
    user=new UserBean();
    user.setId(rs.getString("id"));
    user.setUsername(rs.getString("username"));
    user.setPassword(rs.getString("password"));
    list.add(user);
   }
  } catch (Exception e) {
   e.printStackTrace();
  }
  return list;
}
public static void main(String[] args) {
  List<UserBean> list=findAll();
  for(UserBean lst:list){
   System.out.println("id="+lst.getId());
   System.out.println("username="+lst.getUsername());
   System.out.println("id="+lst.getPassword());
  }
}

}

posted @ 2012-09-04 00:18 abin 閱讀(1549) | 評論 (0) | 編輯收藏

Java數據庫連接池實現

http://06peng.com/read.php/13.htm
http://blog.sina.com.cn/s/blog_70ce7e9e0100v9dh.html
http://blog.163.com/lgw1984_12/blog/static/4122245520096239913479/
http://mzba520.iteye.com/blog/939691
http://blog.csdn.net/java_blue/article/details/6581480
http://blog.csdn.net/a600423444/article/details/6542521
http://blog.csdn.net/caoyinghui1986/article/details/2315864

posted @ 2012-09-03 21:56 abin 閱讀(365) | 評論 (0) | 編輯收藏

java程序實現線程連接池功能

下面是以前學java 的時候寫的一個實現，沒有考慮很多，比如同步處理等等。懶得改，你就看看吧。

package com.wangjia.tools;

import java.io.Serializable;
import java.sql.*;
import java.util.*;

/**
* 數據庫連接池的簡單實現
* @author wangjia
* @version 1.0
*@serial 2301410997974776106L
*/
public class DbConn implements Serializable{

/**
*
*/
private static final long serialVersionUID = 2301410997974776106L;
private static List<Connection> connList=new ArrayList<Connection>();
//private static String driver="com.microsoft.jdbc.sqlserver.SQLServerDriver";//sql2000
private static String driver="com.microsoft.sqlserver.jdbc.SQLServerDriver";//sql2005
private static String url="jdbc:sqlserver://127.0.0.1:1433;DatabaseName=Forum";
private static String userName="sa";
private static String password="sa";
private static int maxConn=20;
private static int minConn=5;
private static int usedConn=0;
private static DbConn dbconn=null;
// private static int flag=1;
/**
* 設置數據庫連接的驅動
* @param driver 數據庫連接的驅動<br/>例如:"com.microsoft.sqlserver.jdbc.SQLServerDriver"
*/
public static void setDriver(String driver) {
DbConn.driver = driver;
}

/**
* 設置數據庫連接池的最小數量
* @param maxConn 數據庫連接池的最小數量
*/
public static void setMaxConn(int maxConn) {
DbConn.maxConn = maxConn;
}

/**
* 設置數據庫連接池的最大數量
* @param minConn 數據庫連接池的最大數量
*/
public static void setMinConn(int minConn) {
DbConn.minConn = minConn;
}

/**
* 設置數據庫連接的URL
* @param url 數據庫連接的URL,包括數據庫的名稱<br/>例如: "jdbc:sqlserver://127.0.0.1:1433;DatabaseName=master"
*/
public static void setUrl(String url) {
DbConn.url = url;
}

private DbConn() throws MyException{
try{
Class.forName(driver);
for(int i=0;i<minConn;i++){
connList.add(DriverManager.getConnection(url,userName.toString(),password.toString()));
}
}catch(ClassNotFoundException e){
throw new MyException("請設置正確的數據庫連接驅動!\nusing: DbConn.setDriver(String driver)");

}catch(SQLException e){
throw new MyException("請設置正確的數據庫連接URL以及用于連接的用戶名和密碼!\n" +
"using: DbConn.setUrl(String url),DbConn.setUserName(String userName),DbConn.setPassword(String password)");

}
}
/**
* 用于得到DbConn對象
* @return 返回一個DbConn對像
*/

public static Connection getConn() throws MyException{
// flag++;
if(dbconn==null)dbconn=new DbConn();
// System.out.println("falg="+flag);
// System.out.println("usedConn="+usedConn);
if(connList.size()==0){
throw new MyException("沒有正確的設置相關信息,以至連接池未初始化");
}
if(usedConn==maxConn){

Thread thread=new Thread(new Runnable(){

@SuppressWarnings("static-access")
public void run() {
if(usedConn<maxConn){
try {
try {
Thread.currentThread().sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
getConn();
} catch (MyException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

}

});
thread.start();
}
if(usedConn>=minConn&&usedConn<maxConn){
try {
connList.add(DriverManager.getConnection(url,userName.toString(),password.toString()));
} catch (SQLException e) {

}
return connList.get(usedConn++);
}
if(usedConn<5){
return connList.get(usedConn++);
}
return null;
}

public static void close(){
try {
if(usedConn>5)
connList.get(--usedConn).close();
else usedConn--;
} catch (SQLException e) {
// TODO 自動生成 catch 塊
e.printStackTrace();
}

}

/**
* 設置用于連接數據庫的密碼
* @param password 用于連接數據庫的密碼
*/
public static void setPassword(String password) {
DbConn.password = password;
}

/**
* 設置用于連接數據庫的用戶名
* @param userName 用于連接數據庫的用戶名
*/
public static void setUserName(String userName) {
DbConn.userName = userName;
}

}

在項目中用到連接池的話，一般會直接使用已有的開源連接池實現，比如用 apache 的common-dbcp.jar和common-pool.jar 相結合，很少去自己實現。

posted @ 2012-09-03 21:55 abin 閱讀(518) | 評論 (0) | 編輯收藏

【學習點滴-memcached】mecached內存管理與原理

http://blog.csdn.net/ohmygirl/article/details/7776013

http://blog.csdn.net/laigood12345/article/details/7350295

posted @ 2012-09-03 13:14 abin 閱讀(488) | 評論 (0) | 編輯收藏

java hession入門實例

1、去官網下載hession的java架包：
官網地址：http://hessian.caucho.com/
我這里下載的是hessian-4.0.7.jar

2、編寫接口：

package com.abin.lee.hession;

public interface IBasicSource {

public String getMessage(String name);

public UserBean getUserBean();

}

3、編寫接口實現類：

package com.abin.lee.hession;

public class BasicSource implements IBasicSource{

public String getMessage(String name) {

return "hello,"+name;

}

public UserBean getUserBean() {

UserBean userBean=new UserBean();

userBean.setId(1);

userBean.setAddress("liangcheng");

userBean.setName("lee");

return userBean;

}

4、實體類，這里需要注意一下，這里必須的實現序列化接口Serializable，因為是需要網絡傳輸的

package com.abin.lee.hession;

import java.io.Serializable;

public class UserBean implements Serializable{

private static final long serialVersionUID = -8931696839145847364L;

private int id;

private String name;

private String address;

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public String getAddress() {

return address;

}

public void setAddress(String address) {

this.address = address;

}

5、配置web.xml

<servlet-name>hessianServlet</servlet-name>

<servlet-class>com.caucho.hessian.server.HessianServlet</servlet-class>

<init-param>

<param-name>home-class</param-name>

<param-value>com.abin.lee.hession.BasicSource</param-value>

</init-param>

<init-param>

<param-name>home-api</param-name>

<param-value>com.abin.lee.hession.IBasicSource</param-value>

</init-param>

</servlet>

<servlet-mapping>

<servlet-name>hessianServlet</servlet-name>

<url-pattern>/hessianServlet</url-pattern>

</servlet-mapping>

6、編寫測試類：

package com.abin.lee.hession.test;

import java.net.MalformedURLException;

import junit.framework.TestCase;

import com.abin.lee.hession.IBasicSource;

import com.abin.lee.hession.UserBean;

import com.caucho.hessian.client.HessianProxyFactory;

public class TestHession extends TestCase{

private static final String HESSION_URL="http://localhost:8081/universal/hessianServlet";

public void testHession() throws MalformedURLException{

HessianProxyFactory factory=new HessianProxyFactory();

IBasicSource basic=(IBasicSource)factory.create(IBasicSource.class, HESSION_URL);

String result=basic.getMessage("abin");

System.out.println("result="+result);

UserBean user=basic.getUserBean();

System.out.println("ID="+user.getId()+",NAME="+user.getName()+",ADDRESS="+user.getAddress());

}

測試結果：

result=hello,abin

ID=1,NAME=lee,ADDRESS=liangcheng

到了這里就成功了。

posted @ 2012-09-02 19:11 abin 閱讀(1896) | 評論 (0) | 編輯收藏

Java enum和方法內部類

package com.abin.lee.collection.inner;

public class XiXiang {

public static enum IdType{

ONE("one"),TWO("two"),THREE("three");

private String textVal;

private IdType(String textVal){

this.textVal=textVal;

}

private String getString(){

return textVal;

}

public static String get(IdType type,String id){

String status=null;

final class get{

String result=null;

public String getName(String id){

if(id.equals("1")){

result="lee";

}

return result;

}

if(type==IdType.valueOf("ONE")){

status=new get().getName(id);

}

return status;

}

public static void main(String[] args) {

String id="1";

IdType type=IdType.valueOf("ONE");

String result=new XiXiang().get(type,id);

System.out.println("result="+result);

}

posted @ 2012-09-02 18:00 abin 閱讀(2384) | 評論 (0) | 編輯收藏

Java 內部類（一）

package com.abin.lee.collection.inner;

public class LiangCheng {

public static String LocalProcess(String wu, String id) {

String well = null;

if (wu.equalsIgnoreCase("abin")) {

LiangCheng liangCheng=new LiangCheng();

LiangCheng.Process process=liangCheng.new Process();

well=process.getNameById(id);

}

return well;

}

public class Process {

private String result = null;

public String getNameById(String id) {

if (id.equalsIgnoreCase("15")) {

result = "lee";

}

return result;

}

public static void main(String[] args) {

LiangCheng liangCheng=new LiangCheng();

String wu="abin";

String id="15";

String result=liangCheng.LocalProcess(wu, id);

System.out.println("result="+result);

}

posted @ 2012-09-02 16:43 abin 閱讀(457) | 評論 (0) | 編輯收藏

Java Stirng和enum相互轉化

package com.abin.lee.collection.enumer;

public class ChangeType {

public static enum stype{

CHINA("china"),JAPAN("japan"),GERMAN("german");

private String textVal;

private stype(String textVal){

this.textVal=textVal;

}

public String toString(){

return textVal;

}

public static void main(String[] args) {

String abin=stype.CHINA.toString();

System.out.println(abin);

stype abing=stype.valueOf("CHINA");//注意這里不應該傳china、japan、german，必須傳CHINA,JAPAN,GERMAN

System.out.println("abing="+abing);

}

posted @ 2012-09-02 15:46 abin 閱讀(416) | 評論 (0) | 編輯收藏

僅列出標題

少年阿賓

常用鏈接

留言簿(22)

我參與的團隊

隨筆分類

隨筆檔案

新聞分類

相冊

搜索

最新評論

閱讀排行榜

評論排行榜