Java Stream Api INNER JOIN兩個列表

Question

如何使用Java Stream Api替換此代碼？

for (Book book : Books.getAllBooks()) { 
     for (SearchResult searchResult : searchResultList) { 
      if (searchResult.getTableName().replace("attr_", "") .equals(book.getTableName())) { 
      bookList.add(book); 
      } 
     } 
     } 

Answer 1

List<Book> bookList = Books.getAllBooks().stream() 
      .filter(e -> searchResultList.stream() 
         .anyMatch(f -> e.getTableName().equals(f.getTableName().replace("attr_", "")))) 
      .collect(Collectors.toList()); 

Answer 2

我從C＃來了，錯過了在Java的API 8這個功能，所以我寫了我自己。 隨着streamjoin你可以寫

Stream<Book> books = 
join(Books.getAllBooks().stream()) 
.withKey(Book::getTableName) 
.on(searchResultList.stream()) 
.withKey(SearchResult::getTableName) 
.combine((book, searchResult) -> book) 
.asStream() 

Answer 3

不正是你問什麼，但這裏有一個技巧，如果你使用的番石榴：

List<Book> bookList = new ArrayList<>(Books.getAllBooks()); 
Lists.transform(bookList, Book::getTableName) 
     .retainAll(Lists.transform(searchResultList, r -> r.getTableName().replace("attr_", ""));