您可以为ResultSet
创建一个包装,使其成为Iterable
。从那里你可以迭代以及创建一个流。当然,你必须定义一个映射函数来获得结果集中的迭代值。
的ResultSetIterable
可能看起来像这样
public class ResultSetIterable<T> implements Iterable<T> {
private final ResultSet rs;
private final Function<ResultSet, T> onNext;
public ResultSetIterable(ResultSet rs, Function<ResultSet, T> onNext){
this.rs = rs;
//onNext is the mapper function to get the values from the resultSet
this.onNext = onNext;
}
@Override
public Iterator<T> iterator() {
try {
return new Iterator<T>() {
//the iterator state is initialized by calling next() to
//know whether there are elements to iterate
boolean hasNext = rs.next();
@Override
public boolean hasNext() {
return hasNext;
}
@Override
public T next() {
T result = onNext.apply(rs);
//after each get, we need to update the hasNext info
try {
hasNext = rs.next();
} catch (SQLException e) {
//you should add proper exception handling here
throw new RuntimeException(e);
}
return result;
}
};
} catch (Exception e) {
//you should add proper exception handling here
throw new RuntimeException(e);
}
}
//adding stream support based on an iteratable is easy
public Stream<T> stream() {
return StreamSupport.stream(this.spliterator(), false);
}
}
现在,我们有我们的包装,你可以流过的结果:如果你想使用一个
ResultSet rs = stmt.executeQuery();
List<String> userIdList = new ResultSetIterable(rs, rs -> rs.getString(1)).stream()
.collect(Collectors.toList())
}
' Stream的工厂方法,因为“迭代直到next()'返回false”,所以你运气不好。“Java 8中不能用它们表示逻辑。Java 9中将支持这种方法,但是,checke d'SQLException'阻止您编写简洁的lambda表达式。你很可能最终会得到一个自定义的'Spliterator',就像在[这个答案](http://stackoverflow.com/a/32232173/2711488)中一样,它涵盖的不仅仅是迭代ResultSet。当你经常使用它时,这对工厂是有用的,但是对于转换单个循环来说,这将是过度的。 – Holger