向界面添加信息

Question

连接.java

public interface Connect {
void commit();
void close();
void setTransactional();
void executeCommand();
}

MainApp.java

public class MainApp {
    public static void main(String[] args) {
        Connect conn=MainApp.getTransactionalConnection();
        conn.executeCommand();
        conn.executeCommand();
        conn.executeCommand();
        conn.executeCommand();
        closeConnection(conn);      
    }
    public static Connect getNormalConnection(){
        return DriverManager.getConnection(); //returns class i have no access to , dont even know its name
    }
    public static Connect getTransactionalConnection(){
        Connect conn =  getNormalConnection();
        conn.setTransactional();
        return conn;
    }
    private static void closeConnection(Connect conn) {
        //something like if connection is transactional then conn.commit();

        conn.close();
    }

}

我得到了 100 个看起来像 main() 的函数。问题是我不想更改这 100 个函数的代码，只需将 1 行 getNormalConnection 更改为 getTransactionalConnection 。我没有访问权限，也不知道实现 Connect 接口的类的名称。无论我是否创建了事务连接，我都只想向 closeConnection() 添加提交。

Answer 1

一个简单的答案是拥有自己的Connect 实现，它要么公开isTransactional 属性，要么在事务性时自动提交，将其他所有内容委托给底层连接：

public class AutoCommitConnect implements Connect {
    private final Connect connect;
    private boolean transactional = false;
    private boolean committed = false;

    public AutoCommitConnect(Connect delegate) {
        this.delegate = delegate;
    }

    public void commit() {
        delegate.commit();
        committed = true;
    }

    public void setTransactional() {
        transactional = true;
        delegate.setTransactional();
    }

    public void close() {
        if (transactional && !committed) {
            commit();
        }
        delegate.close();
    }

    public void executeCommand() {
        delegate.executeCommand();
    }
}

然后更改您的连接返回方法以使用它：

public static Connect getNormalConnection() {
    // getTransactionalConnection will call setTransactional on the wrapper,
    // which will remember that it needs to commit
    return new AutoCommitConnect(DriverManager.getConnection());
}

Answer 2

听起来您想要让接口的实现类具有某些方法的默认实现？
你不能用接口来做到这一点，这就是抽象类的目的。这当然意味着您必须 extend 一个抽象类，而不是 implement 每个类中的一个接口。