class ConnectionManager {
   
  private static Connection connect = null;
   
  public static Connection openConnection() {
    if(connect == null){
      connect = DriverManager.getConnection();
    }
    return connect;
  }
   
  public static void closeConnection() {
    if(connect!=null)
      connect.close();
  }
}

class ConnectionManager {
   
  private Connection connect = null;
   
  public Connection openConnection() {
    if(connect == null){
      connect = DriverManager.getConnection();
    }
    return connect;
  }
   
  public void closeConnection() {
    if(connect!=null)
      connect.close();
  }
}
 
 
class Dao{
  public void insert() {
    ConnectionManager connectionManager = new ConnectionManager();
    Connection connection = connectionManager.openConnection();
     
    //使用connection进行操作
     
    connectionManager.closeConnection();
  }
}

/**
 * Created by IntelliJ IDEA.
 * User: leizhimin
 * Date: 2007-11-23
 * Time: 10:45:02
 * 学生
 */
public class Student {
  private int age = 0;  //年龄
 
  public int getAge() {
    return this.age;
  }
 
  public void setAge(int age) {
    this.age = age;
  }
}
 
/**
 * Created by IntelliJ IDEA.
 * User: leizhimin
 * Date: 2007-11-23
 * Time: 10:53:33
 * 多线程下测试程序
 */
public class ThreadLocalDemo implements Runnable {
  //创建线程局部变量studentLocal，在后面你会发现用来保存Student对象
  private final static ThreadLocal studentLocal = new ThreadLocal();
 
  public static void main(String[] agrs) {
    ThreadLocalDemo td = new ThreadLocalDemo();
    Thread t1 = new Thread(td, "a");
    Thread t2 = new Thread(td, "b");
    t1.start();
    t2.start();
  }
 
  public void run() {
    accessStudent();
  }
 
  /**
   * 示例业务方法，用来测试
   */
  public void accessStudent() {
    //获取当前线程的名字
    String currentThreadName = Thread.currentThread().getName();
    System.out.println(currentThreadName + " is running!");
    //产生一个随机数并打印
    Random random = new Random();
    int age = random.nextInt(100);
    System.out.println("thread " + currentThreadName + " set age to:" + age);
    //获取一个Student对象，并将随机数年龄插入到对象属性中
    Student student = getStudent();
    student.setAge(age);
    System.out.println("thread " + currentThreadName + " first read age is:" + student.getAge());
    try {
      Thread.sleep(500);
    }
    catch (InterruptedException ex) {
      ex.printStackTrace();
    }
    System.out.println("thread " + currentThreadName + " second read age is:" + student.getAge());
  }
 
  protected Student getStudent() {
    //获取本地线程变量并强制转换为Student类型
    Student student = (Student) studentLocal.get();
    //线程首次执行此方法的时候，studentLocal.get()肯定为null
    if (student == null) {
      //创建一个Student对象，并保存到本地线程变量studentLocal中
      student = new Student();
      studentLocal.set(student);
    }
    return student;
  }
}

a is running! 
thread a set age to:76 
b is running! 
thread b set age to:27 
thread a first read age is:76 
thread b first read age is:27 
thread a second read age is:76 
thread b second read age is:27