什么是静态工厂方法？ [英] What are static factory methods?

问题描述

什么是静态工厂方法？

推荐答案

我们避免提供对数据库连接的直接访问，因为它们是资源密集型。所以我们使用静态工厂方法 getDbConnection 创建一个连接，如果我们低于极限。否则，它尝试提供一个备用连接，如果没有异常则失败。

We avoid providing direct access to database connections because they're resource intensive. So we use a static factory method getDbConnection that creates a connection if we're below the limit. Otherwise, it tries to provide a "spare" connection, failing with an exception if there are none.

public class DbConnection
{
   private static final int MAX_CONNS = 100;
   private static int totalConnections = 0;

   private static Set<DbConnection> availableConnections = new HashSet<DbConnection>();

   private DbConnection()
   {
     // ...
     totalConnections++;
   }

   public static DbConnection getDbConnection()
   {
     if(totalConnections < MAX_CONNS)
     {
       return new DbConnection();
     }

     else if(availableConnections.size() > 0)
     {
         DbConnection dbc = availableConnections.iterator().next();
         availableConnections.remove(dbc);
         return dbc;
     }

     else {
       throw new NoDbConnections();
     }
   }

   public static void returnDbConnection(DbConnection dbc)
   {
     availableConnections.add(dbc);
     //...
   }
}

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