何时在 JAVA 中的 glob 语法中使用 **(双星) [英] When to use ** (double star) in glob syntax within JAVA

问题描述

直接来自这个 Java Oracle 教程:

<块引用>

两个星号 ** 的作用与 * 类似，但跨越目录边界.这语法一般用于匹配完整路径.

有人能举出一个真实的例子吗?跨目录边界"是什么意思?跨越目录边界，我想像检查从根目录到 getNameCount()-1 的文件.再举一个真实的例子来解释实践中 * 和 ** 之间的区别会很棒.

解决方案

FileSystem#getPathMatcher() 有一些很好的例子和解释

*.java 匹配表示以 .java 结尾的文件名的路径*.* 匹配包含点的文件名*.{java,class} 匹配以 .java 或 .class 结尾的文件名富.?匹配以 foo 开头的文件名.和单个字符扩展/home/*/* 在 UNIX 平台上匹配/home/gus/data/home/** 在 UNIX 平台上匹配/home/gus 和/home/gus/dataC:\* 在 Windows 平台上匹配 C:foo 和 C:ar(注意反斜杠被转义；作为 Java 语言中的字符串文字，模式将是C:\\*"；)

所以 /home/** 会匹配 /home/gus/data，但 /home/* 不会.>

/home/* 表示 /home 目录中的每个文件.

/home/** 表示 /home 内任何目录中的每个文件.

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* 与 ** 的示例.假设你当前的工作目录是/Users/username/workspace/myproject，那么下面只会匹配./myproject文件(目录).

PathMatcher pathMatcher = FileSystems.getDefault().getPathMatcher("glob:/Users/username/workspace/*");Files.walk(Paths.get(.")).forEach((path) -> {path = path.toAbsolutePath().normalize();System.out.print("路径:"+路径+"");如果(pathMatcher.matches(路径)){System.out.print(匹配");}System.out.println();});

如果使用 **，它将匹配该目录中的所有文件夹和文件.

Directly from this Java Oracle tutorial:

Two asterisks, **, works like * but crosses directory boundaries. This syntax is generally used for matching complete paths.

Could anybody do a real example out of it? What do they mean with "crosses directory boundary"? Crossing the directory boundary, I imagine something like checking the file from root to getNameCount()-1. Again a real example explaining the difference between * and ** in practice would be great.

解决方案

The javadoc for FileSystem#getPathMatcher() has some pretty good examples and explanations

*.java Matches a path that represents a file name ending in .java 
*.*    Matches file names containing a dot 

*.{java,class}  Matches file names ending with .java or .class 
foo.?           Matches file names starting with foo. and a single character extension 
/home/*/*       Matches /home/gus/data on UNIX platforms 
/home/**        Matches /home/gus and /home/gus/data on UNIX platforms 
C:\*           Matches C:foo and C:ar on the Windows platform (note that the backslash is escaped; as a string literal in the Java Language the pattern would be "C:\\*")  

So /home/** would match /home/gus/data, but /home/* wouldn't.

/home/* is saying every file directly in the /home directory.

/home/** is saying every file in any directory inside /home.

---

Example of * vs **. Assuming your current working directory is /Users/username/workspace/myproject, then the following will only match the ./myproject file (directory).

PathMatcher pathMatcher = FileSystems.getDefault().getPathMatcher("glob:/Users/username/workspace/*");
Files.walk(Paths.get(".")).forEach((path) -> {
    path = path.toAbsolutePath().normalize();
    System.out.print("Path: " + path + " ");
    if (pathMatcher.matches(path)) {
        System.out.print("matched");
    }
    System.out.println();
});

If you use **, it will match all folders and files within that directory.

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