本文简单的分析下spring对某个目录下的class资源是如何做到全部的加载

PathMatchingResourcePatternResolver#getResources

PathMatchingResourcePatternResolver是ResourcePatternResolver的实现类，主要实现的方法为getResources(String locationPattern)，具体代码如下，以classpath*:com/question/**/*.class为例

public Resource[] getResources(String locationPattern) throws IOException {        Assert.notNull(locationPattern, "Location pattern must not be null");        //判断查找路径是否以classpath*:开头        if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {            //判断是查找多个文件还是单个，即判断是否含有*或者?            if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {                // a class path resource pattern 即还需要获取根目录                return findPathMatchingResources(locationPattern);            }            else {                // all class path resources with the given name。找寻classpath路径下的根目录全路径，包含jar、zip包                //比如classpath*:com/question/                return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));            }        }        else {            //一般此处针对classpath:开头的资源加载            int prefixEnd = locationPattern.indexOf(":") + 1;            if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {                // a file pattern 加载某个目录                return findPathMatchingResources(locationPattern);            }            else {                // a single resource with the given name优先加载classpath路径下的项目对应资源，找不到才查找jar、zip资源                return new Resource[] {getResourceLoader().getResource(locationPattern)};            }        }    }

PathMatchingResourcePatternResolver#findPathMatchingResources()

protected方法，查找指定路径下的所有资源，同时支持zip、jar中资源的查找

protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {        //首先定位根目录路径，例如classpath*:com/question/        String rootDirPath = determineRootDir(locationPattern);        //默认为**/*.class        String subPattern = locationPattern.substring(rootDirPath.length());        //递归函数的调用，此处会调用PathMatchingResourcePatternResolver#findAllClassPathResources方法加载根目录，找寻classpath路径下的根目录全路径，包含jar、zip包        Resource[] rootDirResources = getResources(rootDirPath);                Set
    
      result = new LinkedHashSet
     
      (16);        for (Resource rootDirResource : rootDirResources) {            //判断是否含有协议为bundle的资源，没有则返回原值            rootDirResource = resolveRootDirResource(rootDirResource);            //vfs协议            if (rootDirResource.getURL().getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {                result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirResource, subPattern, getPathMatcher()));            }            //jar协议、zip协议、wsjar协议、vfszip协议            else if (isJarResource(rootDirResource)) {                //从jar包中找寻相应的所有class文件                result.addAll(doFindPathMatchingJarResources(rootDirResource, subPattern));            }            else {                //加载非jar、zip包的项目资源                result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));            }        }        if (logger.isDebugEnabled()) {            logger.debug("Resolved location pattern [" + locationPattern + "] to resources " + result);        }        return result.toArray(new Resource[result.size()]);    }
     
    

为了理解得更清楚，我们再抽取必要的代码进行分析，比如PathMatchingResourcePatternResolver#findAllClassPathResources()和PathMatchingResourcePatternResolver#doFindPathMatchingFileResources()

• PathMatchingResourcePatternResolver#findAllClassPathResources
  通过classloader来加载资源目录，代码如下

protected Resource[] findAllClassPathResources(String location) throws IOException {        String path = location;        //例如com/question/        if (path.startsWith("/")) {            path = path.substring(1);        }        //真实查找方法        Set
    
      result = doFindAllClassPathResources(path);        return result.toArray(new Resource[result.size()]);    }
    

进而看PathMatchingResourcePatternResolver#doFindAllClassPathResources()

protected Set
    
      doFindAllClassPathResources(String path) throws IOException {        Set
     
       result = new LinkedHashSet
      
       (16);        ClassLoader cl = getClassLoader();        //通过classloader来加载资源目录，这里也会去找寻classpath路径下的jar包或者zip包        Enumeration
       
         resourceUrls = (cl != null ? cl.getResources(path) : ClassLoader.getSystemResources(path));        while (resourceUrls.hasMoreElements()) {            URL url = resourceUrls.nextElement();            //对找到的路径保存为UrlResource对象放入set集合中            result.add(convertClassLoaderURL(url));        }        if ("".equals(path)) {            //加载jar协议的资源            addAllClassLoaderJarRoots(cl, result);        }        return result;    }
       
      
     
    

Note：一般而言找到的结果为一个，也就是file协议的项目工程资源目录，不建议查找的base-package含有jar包的资源目录，比如org.springframework

• PathMatchingResourcePatternResolver#doFindPathMatchingFileResources()
  查找指定目录下的所有文件，这里特指class文件

protected Set
    
      doFindPathMatchingFileResources(Resource rootDirResource, String subPattern)            throws IOException {        File rootDir;        try {            //获取绝对路径对应的file            rootDir = rootDirResource.getFile().getAbsoluteFile();        }        catch (IOException ex) {            if (logger.isWarnEnabled()) {                logger.warn("Cannot search for matching files underneath " + rootDirResource +                        " because it does not correspond to a directory in the file system", ex);            }            //异常则返回空的集合            return Collections.emptySet();        }        return doFindMatchingFileSystemResources(rootDir, subPattern);    }
    

进而看真实的查找方法doFindMatchingFileSystemResources()，代码如下

protected Set
    
      doFindMatchingFileSystemResources(File rootDir, String subPattern) throws IOException {        if (logger.isDebugEnabled()) {            logger.debug("Looking for matching resources in directory tree [" + rootDir.getPath() + "]");        }        //真实的调用方法        Set
     
       matchingFiles = retrieveMatchingFiles(rootDir, subPattern);        Set
      
        result = new LinkedHashSet
       
        (matchingFiles.size());        for (File file : matchingFiles) {            //对查找到的资源包装为FileSystemResource对象            result.add(new FileSystemResource(file));        }        return result;    }
       
      
     
    

继续观察真实加载文件资源的方法retriveMatchingFiles()，代码如下

protected Set
    
      retrieveMatchingFiles(File rootDir, String pattern) throws IOException {        //根目录不存在？返回空集合        if (!rootDir.exists()) {            // Silently skip non-existing directories.            if (logger.isDebugEnabled()) {                logger.debug("Skipping [" + rootDir.getAbsolutePath() + "] because it does not exist");            }            return Collections.emptySet();        }        //不是目录？返回为空        if (!rootDir.isDirectory()) {            // Complain louder if it exists but is no directory.            if (logger.isWarnEnabled()) {                logger.warn("Skipping [" + rootDir.getAbsolutePath() + "] because it does not denote a directory");            }            return Collections.emptySet();        }        //不可读？返回为空        if (!rootDir.canRead()) {            if (logger.isWarnEnabled()) {                logger.warn("Cannot search for matching files underneath directory [" + rootDir.getAbsolutePath() +                        "] because the application is not allowed to read the directory");            }            return Collections.emptySet();        }        //转换根目录全路径为标准的查找路径        String fullPattern = StringUtils.replace(rootDir.getAbsolutePath(), File.separator, "/");        if (!pattern.startsWith("/")) {            fullPattern += "/";        }        //查找类型为.class文件        fullPattern = fullPattern + StringUtils.replace(pattern, File.separator, "/");        Set
     
       result = new LinkedHashSet
      
       (8);        doRetrieveMatchingFiles(fullPattern, rootDir, result);        return result;    }
      
     
    

接着瞧doRetriveMathingFiles的重载方法，代码如下

protected void doRetrieveMatchingFiles(String fullPattern, File dir, Set
    
      result) throws IOException {        if (logger.isDebugEnabled()) {            logger.debug("Searching directory [" + dir.getAbsolutePath() +                    "] for files matching pattern [" + fullPattern + "]");        }        //从根目录开始罗列文件集合        File[] dirContents = dir.listFiles();        if (dirContents == null) {            //查找到没有了则直接返回            if (logger.isWarnEnabled()) {                logger.warn("Could not retrieve contents of directory [" + dir.getAbsolutePath() + "]");            }            return;        }        //遍历        for (File content : dirContents) {            //获取当前文件路径            String currPath = StringUtils.replace(content.getAbsolutePath(), File.separator, "/");            //查找到的子文件仍是目录且以根目录为开头            if (content.isDirectory() && getPathMatcher().matchStart(fullPattern, currPath + "/")) {                if (!content.canRead()) {                    if (logger.isDebugEnabled()) {                        logger.debug("Skipping subdirectory [" + dir.getAbsolutePath() +                                "] because the application is not allowed to read the directory");                    }                }                else {                    //递归调用查找所有的文件                    doRetrieveMatchingFiles(fullPattern, content, result);                }            }            //查看当前文件路径是否满足**/*.class格式，满足则添加            if (getPathMatcher().match(fullPattern, currPath)) {                result.add(content);            }        }    }
    

小结

1. classpath*:表示查找classpath路径下的所有符合条件的资源，包含jar、zip等资源；classpath:表示优先在项目的资源目录下查找，找不到才去jar、zip等资源中查找

2. 该类可以帮助spring查找到符合ant-style格式的所有资源，所以富有借鉴意义。附：ant-style指的是类似*/?此类的匹配字符