jar包执行时访问资源文件造成的FileSystemNotFoundException问题

问题描述

在Java项目中，若需要访问资源文件，通常使用getClass().getResource("/xxx")和getClass().getResourceAsStream("/")来获取资源文件，后一种方式获取到的是InputStream，一般不会出现什么问题，但是通过第一种获取资源URL的方式，在IDEA中执行时没有问题，但是在服务器环境执行时，会出现java.nio.file.FileSystemNotFoundException，之前遇到这个问题我没有在意，只是换成getResourceAsStream后就解决了，但是后来遇到一个需要递归访问资源文件目录，我使用的Files.walkFileTree方法，直接获取输入流的方案不适合我，随后发现其实只要是打成jar包执行的时候，通过Files和Path去访问资源文件，getResource就会抛出FileSystemNotFoundException，并非服务器环境的问题，因为jar包执行时，文件系统与IDE中直接执行时不一样，所以会抛出这个异常。
原始的代码如下：

Path configDir = Paths.get(
                    LocalConfigDataFlowManager.class.getResource(
                            "/"
                    ).toURI().getPath(), "flow-config"
            );
List> config = new ArrayList<>();
Files.walkFileTree(
        configDir,
        new HashSet<>(),
        1,
        new FileVisitor() {
        ......

报错信息如下：

java.nio.file.FileSystemNotFoundException
        at jdk.zipfs/jdk.nio.zipfs.ZipFileSystemProvider.getFileSystem(ZipFileSystemProvider.java:169)
        at jdk.zipfs/jdk.nio.zipfs.ZipFileSystemProvider.getPath(ZipFileSystemProvider.java:155)
        at java.base/java.nio.file.Path.of(Path.java:208)
        at java.base/java.nio.file.Paths.get(Paths.java:97)
        at ink.andromeda.dataflow.core.flow.ConfigurableDataFlowManager.(ConfigurableDataFlowManager.java:305)
        at ink.andromeda.dataflow.demo.LocalConfigDataFlowManager.(LocalConfigDataFlowManager.java:25)
        at ink.andromeda.dataflow.demo.DataFlowDemoApplication.dataFlowManager(DataFlowDemoApplication.java:51)
        at ink.andromeda.dataflow.demo.DataFlowDemoApplication$$EnhancerBySpringCGLIB$$73b01d37.CGLIB$dataFlowManager$0()
        ......
......
2021-01-07.22:34:39.649 ERROR TraceId[] [main] i.a.d.d.LocalConfigDataFlowManager.visitFileFailed:60 null/flow-config
java.nio.file.NoSuchFileException: null/flow-config
        at java.base/sun.nio.fs.UnixException.translateToIOException(UnixException.java:92)
        at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111)
        at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:116)
        at java.base/sun.nio.fs.UnixFileAttributeViews$Basic.readAttributes(UnixFileAttributeViews.java:55)
        at java.base/sun.nio.fs.UnixFileSystemProvider.readAttributes(UnixFileSystemProvider.java:149)
        at java.base/java.nio.file.Files.readAttributes(Files.java:1763)
        at java.base/java.nio.file.FileTreeWalker.getAttributes(FileTreeWalker.java:219)
        at java.base/java.nio.file.FileTreeWalker.visit(FileTreeWalker.java:276)
        at java.base/java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:322)
        at java.base/java.nio.file.Files.walkFileTree(Files.java:2716)
        at ink.andromeda.dataflow.demo.LocalConfigDataFlowManager.getFlowConfig(LocalConfigDataFlowManager.java:39)
        at ink.andromeda.dataflow.core.flow.ConfigurableDataFlowManager.reload(ConfigurableDataFlowManager.java:92)
        at ink.andromeda.dataflow.core.flow.ConfigurableDataFlowManager.init(ConfigurableDataFlowManager.java:56)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        ......

解决方案

刚开始试了如下方案：

Path configDir = FileSystems.getDefault().getPath(new UrlResource(this.getClass().getResource("/flow-config").toURI()).toString());

但是仍然有问题：

2021-01-07.23:06:42.037 ERROR TraceId[] [main] i.a.d.d.LocalConfigDataFlowManager.visitFileFailed:63 URL [jar:file:/Users/windlively/IdeaProjects/data-flow/data-flow-demo/target/data-flow-demo-1.0-SNAPSHOT.jar!/BOOT-INF/classes!/flow-config]
java.nio.file.NoSuchFileException: URL [jar:file:/Users/windlively/IdeaProjects/data-flow/data-flow-demo/target/data-flow-demo-1.0-SNAPSHOT.jar!/BOOT-INF/classes!/flow-config]
        at java.base/sun.nio.fs.UnixException.translateToIOException(UnixException.java:92)
        at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111)
        at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:116)
        at java.base/sun.nio.fs.UnixFileAttributeViews$Basic.readAttributes(UnixFileAttributeViews.java:55)
        at java.base/sun.nio.fs.UnixFileSystemProvider.readAttributes(UnixFileSystemProvider.java:149)
        at java.base/java.nio.file.Files.readAttributes(Files.java:1763)
        at java.base/java.nio.file.FileTreeWalker.getAttributes(FileTreeWalker.java:219)
        at java.base/java.nio.file.FileTreeWalker.visit(FileTreeWalker.java:276)
        at java.base/java.nio.file.FileTreeWalker.walk(FileTreeWalker.java:322)
        at java.base/java.nio.file.Files.walkFileTree(Files.java:2716)
        at ink.andromeda.dataflow.demo.LocalConfigDataFlowManager.getFlowConfig(LocalConfigDataFlowManager.java:42)
        at ink.andromeda.dataflow.core.flow.ConfigurableDataFlowManager.reload(ConfigurableDataFlowManager.java:92)
        at ink.andromeda.dataflow.core.flow.ConfigurableDataFlowManager.init(ConfigurableDataFlowManager.java:56)

于是继续查询资料，在stackoverflow上看到了一个利用Spring的@Value()注解和Spring Resource来访问资源文件的替代方案，而且提供了遍历资源文件夹的方法。
首先在Bean中加入一个字段并用Value注解注入资源文件的位置：

@Value("classpath:/flow-config/**")
private Resource[] flowConfigResources;

Spring会自动将classes根目录flow-config文件夹下的资源文件全部注入到flowConfigResources字段中去。
然后修改原先的代码如下：

protected List> getFlowConfig() {
    return Stream.of(flowConfigResources)
            .filter(s -> Objects.nonNull(s.getFilename()))
            .filter(s -> s.getFilename().matches("^sync-config-[\\w-]+?.json$"))
            .map(flowConfigResource -> {
                try (InputStream is = flowConfigResource.getInputStream()) {
                    ByteArrayOutputStream os = new ByteArrayOutputStream();
                    int data;
                    while ((data = is.read()) != -1) os.write(data);
                    //noinspection unchecked
                    return (Map) GSON().fromJson(os.toString(StandardCharsets.UTF_8.name()),
                            new TypeToken>() {
                            }.getType());

                } catch (IOException ex) {
                    throw new IllegalStateException(ex);
                }
            })
            .filter(Objects::nonNull)
            .collect(Collectors.toList());
}

过滤和遍历Spring注入的Resource列表，即可读取到此文件夹下所有需要的资源文件，打成jar包之后也可正常运行。