spring如何解析通配符路徑

轉自：　http://goodscript.iteye.com/blog/1161519

在spring的配置文件中、經常看見類似這樣的配置路徑： 

classpath:/com/module/**/*sql.xml

系統會根據配置路徑自動加載符合路徑規則的xml文件 
假如讓你實現這樣的功能： 
根據一個通配符路徑加載符合規則的xml文件你會怎麼做？ 

先看一個小例子： 

import java.io.IOException;

import org.springframework.core.io.Resource;
import org.springframework.core.io.support.PathMatchingResourcePatternResolver;
import org.springframework.core.io.support.ResourcePatternResolver;

public class XMLManager {

    private String location = "classpath:*.xml";

    public void readFile() throws IOException {
        ResourcePatternResolver resourceLoader = new PathMatchingResourcePatternResolver();
        Resource[] source = resourceLoader.getResources(location);
        for (int i = 0; i < source.length; i++) {
            Resource resource = source[i];
            System.out.println(resource.getFilename());

        }
    }

    public static void main(String[] args) {

        XMLManager m = new XMLManager();
        try {
            m.readFile();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

輸出結果： 

applicationContext.xml
logback.xml
menu_my.xml

是不是很簡單？ 
只要調用PathMatchingResourcePatternResolver的getResources方法就可以實現我們想要的功能。 
下面深入研究一下spring的源碼PathMatchingResourcePatternResolver： 
1、getResources方法 

public Resource[] getResources(String locationPattern) throws IOException {
        Assert.notNull(locationPattern, "Location pattern must not be null");
        if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {
            // a class path resource (multiple resources for same name possible)
            if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {
                // a class path resource pattern
                return findPathMatchingResources(locationPattern);
            }
            else {
                // all class path resources with the given name
                return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));
            }
        }
        else {
            // Only look for a pattern after a prefix here
            // (to not get fooled by a pattern symbol in a strange prefix).
            int prefixEnd = locationPattern.indexOf(":") + 1;
            if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {
                // a file pattern
                return findPathMatchingResources(locationPattern);
            }
            else {
                // a single resource with the given name
                return new Resource[] {getResourceLoader().getResource(locationPattern)};
            }
        }
    }

該方法主要是判斷locationPattern是否包含有通配符、如果包含通配符則調用findPathMatchingResources方法、沒有包含通配符就不需要解析了 
2、findPathMatchingResources方法 

protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {
    String rootDirPath = determineRootDir(locationPattern);
    String subPattern = locationPattern.substring(rootDirPath.length());
    Resource[] rootDirResources = getResources(rootDirPath);
    Set<Resource> result = new LinkedHashSet<Resource>(16);
    for (Resource rootDirResource : rootDirResources) {
        rootDirResource = resolveRootDirResource(rootDirResource);
        if (isJarResource(rootDirResource)) {
            result.addAll(doFindPathMatchingJarResources(rootDirResource, subPattern));
        }
        else if (rootDirResource.getURL().getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
            result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirResource, subPattern, getPathMatcher()));
        }
        else {
            result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));
        }
    }
    if (logger.isDebugEnabled()) {
        logger.debug("Resolved location pattern [" + locationPattern + "] to resources " + result);
    }
    return result.toArray(new Resource[result.size()]);
}

把locationPattern拆分成兩部分：rootDirPath 和subPattern 
rootDirPath是根目錄路徑 
subPattern是子目錄路徑匹配規則字符串 
歷遍根目錄下的所有子目錄、並得到所有的子目錄 
在doFindPathMatchingFileResources(rootDirResource, subPattern)方法中 
再根據子目錄逐個逐個去匹配subPattern 
3、doFindPathMatchingFileResources 

protected Set<Resource> doFindPathMatchingFileResources(Resource rootDirResource, String subPattern)
        throws IOException {

    File rootDir;
    try {
        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);
        }
        return Collections.emptySet();
    }
    return doFindMatchingFileSystemResources(rootDir, subPattern);
}

跳轉到另一個方法doFindMatchingFileSystemResources： 

protected Set<Resource> doFindMatchingFileSystemResources(File rootDir, String subPattern) throws IOException {
    if (logger.isDebugEnabled()) {
        logger.debug("Looking for matching resources in directory tree [" + rootDir.getPath() + "]");
    }
    Set<File> matchingFiles = retrieveMatchingFiles(rootDir, subPattern);
    Set<Resource> result = new LinkedHashSet<Resource>(matchingFiles.size());
    for (File file : matchingFiles) {
        result.add(new FileSystemResource(file));
    }
    return result;
}

retrieveMatchingFiles 

protected Set<File> retrieveMatchingFiles(File rootDir, String pattern) throws IOException {
    if (!rootDir.exists()) {
        // Silently skip non-existing directories.
        if (logger.isDebugEnabled()) {
            logger.debug("Skipping [" + rootDir.getAbsolutePath() + "] because it does not exist");
        }
        return Collections.emptySet();
    }
    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();
    }
    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();
    }
    String fullPattern = StringUtils.replace(rootDir.getAbsolutePath(), File.separator, "/");
    if (!pattern.startsWith("/")) {
        fullPattern += "/";
    }
    fullPattern = fullPattern + StringUtils.replace(pattern, File.separator, "/");
    Set<File> result = new LinkedHashSet<File>(8);
    doRetrieveMatchingFiles(fullPattern, rootDir, result);
    return result;
}

調用遞歸方法： 
doRetrieveMatchingFiles 

protected void doRetrieveMatchingFiles(String fullPattern, File dir, Set<File> result) throws IOException {
    if (logger.isDebugEnabled()) {
        logger.debug("Searching directory [" + dir.getAbsolutePath() +
                "] for files matching pattern [" + fullPattern + "]");
    }
    File[] dirContents = dir.listFiles();
    if (dirContents == null) {
        if (logger.isWarnEnabled()) {
            logger.warn("Could not retrieve contents of directory [" + dir.getAbsolutePath() + "]");
        }
        return;
    }
    for (File content : dirContents) {
        String currPath = StringUtils.replace(content.getAbsolutePath(), File.separator, "/");
        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 {
                doRetrieveMatchingFiles(fullPattern, content, result);
            }
        }
        if (getPathMatcher().match(fullPattern, currPath)) {
            result.add(content);
        }
    }
}