设计模式课程 设计模式精讲 17-3 模板方法模式源码解析

1　　　　源码解析

1.1　　　　源码解析1(在jdk中的使用)

1.2　　　　源码解析2（在servlet中的应用）

1.3　　　　源码解析3（在mybaties中的应用）

1　　　　源码解析

1.1　　　　源码解析1(在jdk中的使用)

AbstractList（父类）

public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {

//get方法为抽象方法，完全交给子类去实现

abstract public E get(int index);

}

ArrayList（子类）

public class ArrayList<E> extends AbstractList<E>
        implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
//子类来实现get方法
 public E get(int index) {
        rangeCheck(index);

        return elementData(index);
    }
}

同理：AbstractSet，AbstractMap同样采用了模版方法模式

1.2　　　　源码解析2（在servlet中的应用）

HttpServlet

public abstract class HttpServlet extends GenericServlet {
/***
   *    doget方法，dopost方法，service方法
   *     httpServlet中定义了一套模版，我们使用的时候只要继承httpServlet，并且实现doget和dopost方法就可以了
   *     注意：权限是protected，也就是只有子类才能实现这些方法
   */

//doget方法
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_get_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(405, msg);
        } else {
            resp.sendError(400, msg);
        }

    }

//dopost方法
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String protocol = req.getProtocol();
        String msg = lStrings.getString("http.method_post_not_supported");
        if (protocol.endsWith("1.1")) {
            resp.sendError(405, msg);
        } else {
            resp.sendError(400, msg);
        }

    }
}

1.3　　　　源码解析3（在mybaties中的应用）

uml类图：

BaseExecutor（父类）

public abstract class BaseExecutor implements Executor {
//这是一个执行sql的类
//其中有四个方法，重点看doUpdate方法，
//它有四个子类，分别是在简单sql doupdate，复用sql doupdate，批量sql doupdate，等

   protected abstract int doUpdate(MappedStatement var1, Object var2) throws SQLException;

    protected abstract List<BatchResult> doFlushStatements(boolean var1) throws SQLException;

    protected abstract <E> List<E> doQuery(MappedStatement var1, Object var2, RowBounds var3, ResultHandler var4, BoundSql var5) throws SQLException;

    protected abstract <E> Cursor<E> doQueryCursor(MappedStatement var1, Object var2, RowBounds var3, BoundSql var4) throws SQLException;

}

子类BatchExecutor ：

public class BatchExecutor extends BaseExecutor {
　　@Override
  public int doUpdate(MappedStatement ms, Object parameterObject) throws SQLException {
    final Configuration configuration = ms.getConfiguration();
    final StatementHandler handler = configuration.newStatementHandler(this, ms, parameterObject, RowBounds.DEFAULT, null, null);
    final BoundSql boundSql = handler.getBoundSql();
    final String sql = boundSql.getSql();
    final Statement stmt;
    if (sql.equals(currentSql) && ms.equals(currentStatement)) {
      int last = statementList.size() - 1;
      stmt = statementList.get(last);
      applyTransactionTimeout(stmt);
     handler.parameterize(stmt);//fix Issues 322
      BatchResult batchResult = batchResultList.get(last);
      batchResult.addParameterObject(parameterObject);
    } else {
      Connection connection = getConnection(ms.getStatementLog());
      stmt = handler.prepare(connection, transaction.getTimeout());
      handler.parameterize(stmt);    //fix Issues 322
      currentSql = sql;
      currentStatement = ms;
      statementList.add(stmt);
      batchResultList.add(new BatchResult(ms, sql, parameterObject));
    }
  // handler.parameterize(stmt);
    handler.batch(stmt);
    return BATCH_UPDATE_RETURN_VALUE;
  }

}

子类SimpleExecutor ：

public class SimpleExecutor extends BaseExecutor {
  @Override
  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Statement stmt = null;
    try {
      Configuration configuration = ms.getConfiguration();
      StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
      stmt = prepareStatement(handler, ms.getStatementLog());
      return handler.update(stmt);
    } finally {
      closeStatement(stmt);
    }
  }
}

原文地址：https://www.cnblogs.com/1446358788-qq/p/11562083.html