Java 學習記錄94 — Read Existing Directory Contents

這邊創了三個資料夾，跟好幾個文檔，各層級關係可以到下方我的 Github 去看

package nonBlockingIO.path.copyExamples;
import java.io.IOException;
import java.nio.file.*;
public class ReadDirectory {
    public static void main(String[] args) {
        Path directory = FileSystems.getDefault().getPath("src/nonBlockingIO/path/copyExamples/Dir2");
        try (DirectoryStream<Path> contents = Files.newDirectoryStream(directory)) {
            for (Path file : contents) {
                System.out.println(file.getFileName());
            }
        } catch (IOException | DirectoryIteratorException e) {
            System.out.println(e.getMessage());
        }
    }
}

輸出結果：

Dir3

file1.txt

file2.txt

file3.txt

遍歷指定位置的所有檔案，但不會進到更下一層，像是資料夾Dir3裡面還有其他資料夾跟資料

try (DirectoryStream<Path> contents = Files.newDirectoryStream(directory, "*.dat")) {

輸出結果：

file3.dat

指定搜尋結尾是 .dat 的檔案

package nonBlockingIO.path.copyExamples;
import java.io.IOException;
import java.nio.file.*;
public class ReadDirectory {
    public static void main(String[] args) {
        DirectoryStream.Filter<Path> filter =
                new DirectoryStream.Filter<Path>() {
                    @Override
                    public boolean accept(Path entry) throws IOException {
                        return (Files.isRegularFile(entry));
                    }
                };
        Path directory = FileSystems.getDefault().getPath("src/nonBlockingIO/path/copyExamples/Dir2");
//        try (DirectoryStream<Path> contents = Files.newDirectoryStream(directory, "*.dat")) {
        try (DirectoryStream<Path> contents = Files.newDirectoryStream(directory, filter)) {
            for (Path file : contents) {
                System.out.println(file.getFileName());
            }
        } catch (IOException | DirectoryIteratorException e) {
            System.out.println(e.getMessage());
        }
    }
}

輸出結果：

file1.txt

file2.txt

file3.dat

比較複雜的寫法，過濾出指定資料夾的所有檔案

DirectoryStream.Filter<Path> filter = p -> Files.isRegularFile(p);
Path directory = FileSystems.getDefault().getPath("src/nonBlockingIO/path/copyExamples/Dir2");
//        try (DirectoryStream<Path> contents = Files.newDirectoryStream(directory, "*.dat")) {
try (DirectoryStream<Path> contents = Files.newDirectoryStream(directory, filter)) {
    for (Path file : contents) {
        System.out.println(file.getFileName());
    }
} catch (IOException | DirectoryIteratorException e) {
    System.out.println(e.getMessage());
}

輸出結果：

file1.txt

file2.txt

file3.dat

另一種寫法，這個叫做 Lambda expression

上面代碼全都紀錄在我的 Github