java - 使用 jool java 8 使用 Seq、Tuple 和 Streams 进行左外连接

Question

我有两个 Lists Customers 和 Address，它们的共同值是 pmtxnid。我想使用 jool(java 8) leftouterjoin 方法，但我不知道正确的语法。也没有我可以更简单地理解它的例子。如果有人知道 Seq，Tuples jool with java 8 Streams，请帮忙。

List<Customers> customers = new ArrayList<Customers>();
    customers.add(new Customers(16079391, 12, "A")); // NULL
    customers.add(new Customers(16079392, 13, "B")); // 2
    customers.add(new Customers(16079393, 14, "C")); // NULL
    customers.add(new Customers(16079394, 15, "D")); // BIll
    customers.add(new Customers(16079395, 16, "E")); // 1

    List<Address> addresses = new ArrayList<Address>();
    addresses.add(new Address(1, 16079392, "bangalore", "karnataka"));
    addresses.add(new Address(2, 16079392, "chennai", "tamil nadu"));
    addresses.add(new Address(3, 16079392, "hyderabad", "telanagana"));
    addresses.add(new Address(4, 16079395, "indore", "mp"));
    addresses.add(new Address(5, 16079395, "kanpur", "up"));

Seq<List<Customers>> s1 = Seq.of(customers);
    Seq<List<Address>> s2 = Seq.of(addresses);

我尝试了下面的代码但没有成功。

Seq<Tuple2<Seq<List<Customers>>, Seq<List<Address>>>> loj=  Seq.of(s1).leftOuterJoin(Seq.of(s2), (t, u) -> Objects.equals(t, u));

Answer 1

假设可以分别使用 Customers#getPmtxnid() 和 Address#getPmtxnid() 访问公共(public) pmtxnid 值，leftOuterJoin () 调用应如下所示:

var result = Seq.of(s1).leftOuterJoin(Seq.of(s2),
    (c, a) -> Objects.equals(c.getPmtxnid(), a.getPmtxnid()));

注意 Objects#equals() 只有当其中一个对象可以有一个 null pmtxnid 时才需要。