Java 8 Friday Goodies：java.io终于成功了！

在Data Geekery ，我们喜欢Java。而且，由于我们真的很喜欢jOOQ的流畅的API和查询DSL ，我们对Java 8将为我们的生态系统带来什么感到非常兴奋。我们已经写了一些关于Java 8好东西的博客，现在我们觉得是时候开始一个新的博客系列了……

Java 8星期五

每个星期五，我们都会向您展示一些不错的教程风格的Java 8新功能，这些功能利用了lambda表达式，扩展方法和其他好东西。您可以在GitHub上找到源代码。

Java 8 Goodie：带有Lambdas的java.io

与文件系统进行交互在Java中有些痛苦。 CTMMC向我们展示了如何使用Java复制文件的示例。尽管仍然存在一些问题，至少，我们现在可以使用lambda和新的Streams API 遍历文件系统并列出文件！这是我们已推送到GitHub存储库的FileFilterGoodies示例：

public class FileFilterGoodies {public static void main(String args[]) {listRecursive(new File("."));}/*** This method recursively lists all* .txt and .java files in a directory*/private static void listRecursive(File dir) {Arrays.stream(dir.listFiles((f, n) ->!n.startsWith(".")&&(f.isDirectory()||  n.endsWith(".txt")||  n.endsWith(".java")))).forEach(unchecked((file) -> {System.out.println(file.getCanonicalPath().substring(new File(".").getCanonicalPath().length()));if (file.isDirectory()) {listRecursive(file);}}));}/*** This utility simply wraps a functional* interface that throws a checked exception* into a Java 8 Consumer*/private static <T> Consumer<T>unchecked(CheckedConsumer<T> consumer) {return t -> {try {consumer.accept(t);}catch (Exception e) {throw new RuntimeException(e);}};}@FunctionalInterfaceprivate interface CheckedConsumer<T> {void accept(T t) throws Exception;}
}

上面程序的输出是：

\jOOQ's Java 8 Goodies.iml
\LICENSE.txt
\out
\out\production
\out\production\jOOQ's Java 8 Goodies
\out\production\jOOQ's Java 8 Goodies\org
\out\production\jOOQ's Java 8 Goodies\org\jooq
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8\goodies
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8\goodies\io
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8\goodies\io\FileFilterGoodies$CheckedConsumer.class
\out\production\jOOQ's Java 8 Goodies\org\jooq\java8\goodies\io\FileFilterGoodies.class
\README.txt
\src
\src\org
\src\org\jooq
\src\org\jooq\java8
\src\org\jooq\java8\goodies
\src\org\jooq\java8\goodies\io
\src\org\jooq\java8\goodies\io\FileFilterGoodies.java

现在，这真的很棒，不是吗？让我们分解上面的listRecursive()方法：

// With this method, we wrap the File[] array
// into a new Java 8 Stream, which has awesome
// new methods.
Arrays.stream(// The Java 1.2 File.listFiles() method luckily
// accepts a @FunctionalInterface, which can be
// instantiated using a lambda expression
// ...
// In this example, we'll just ignore the fact
// that listFiles can return nulldir.listFiles((f, n) ->!n.startsWith(".")&&(f.isDirectory()||  n.endsWith(".txt")||  n.endsWith(".java"))))// Each Stream (and also java.util.List) has this
// awesome forEach method, that accepts a Consumer.forEach(// Unfortunately, Java 8 Consumers don't allow
// throwing checked exceptions. So let's quickly
// wrap it (see details below) ...unchecked(// ... and pass another lambda expression to it,
// which prints the local path and recurses(file) -> {System.out.println(file.getCanonicalPath().substring(new File(".").getCanonicalPath().length()));if (file.isDirectory()) {listRecursive(file);}}));