本文簡單的分析下spring對某個目錄下的class資源是如何做到全部的加載
PathMatchingResourcePatternResolver#getResources
PathMatchingResourcePatternResolver是ResourcePatternResolver的實現類，主要實現的方法為getResources(String locationPattern)，具體代碼如下，以classpath*:com/question/**/*.class為例
public Resource[] getResources(String locationPattern) throws IOException {
Assert.notNull(locationPattern, "Location pattern must not be null");
//判斷查找路徑是否以classpath*:開頭
if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {
//判斷是查找多個文件還是單個，即判斷是否含有*或者?
if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {
// a class path resource pattern 即還需要獲取根目錄
return findPathMatchingResources(locationPattern);
}
else {
// all class path resources with the given name。找尋classpath路徑下的根目錄全路徑，包含jar、zip包
//比如classpath*:com/question/
return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));
}
}
else {
//一般此處針對classpath:開頭的資源加載
int prefixEnd = locationPattern.indexOf(":") + 1;
if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {
// a file pattern 加載某個目錄
return findPathMatchingResources(locationPattern);
}
else {
// a single resource with the given name優先加載classpath路徑下的項目對應資源，找不到才查找jar、zip資源
return new Resource[] {getResourceLoader().getResource(locationPattern)};
}
}
}
PathMatchingResourcePatternResolver#findPathMatchingResources()
protected方法，查找指定路徑下的所有資源，同時支持zip、jar中資源的查找
protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {
//首先定位根目錄路徑，例如classpath*:com/question/
String rootDirPath = determineRootDir(locationPattern);
//默認為**/*.class
String subPattern = locationPattern.substring(rootDirPath.length());
//遞歸函數的調用，此處會調用PathMatchingResourcePatternResolver#findAllClassPathResources方法加載根目錄，找尋classpath路徑下的根目錄全路徑，包含jar、zip包
Resource[] rootDirResources = getResources(rootDirPath);
Set<Resource> result = new LinkedHashSet<Resource>(16);
for (Resource rootDirResource : rootDirResources) {
//判斷是否含有協議為bundle的資源，沒有則返回原值
rootDirResource = resolveRootDirResource(rootDirResource);
//vfs協議
if (rootDirResource.getURL().getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirResource, subPattern, getPathMatcher()));
}
//jar協議、zip協議、wsjar協議、vfszip協議
else if (isJarResource(rootDirResource)) {
//從jar包中找尋相應的所有class文件
result.addAll(doFindPathMatchingJarResources(rootDirResource, subPattern));
}
else {
//加載非jar、zip包的項目資源
result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));
}
}
if (logger.isDebugEnabled()) {
logger.debug("Resolved location pattern [" + locationPattern + "] to resources " + result);
}
return result.toArray(new Resource[result.size()]);
}
為了理解得更清楚，我們再抽取必要的代碼進行分析，比如PathMatchingResourcePatternResolver#findAllClassPathResources()和PathMatchingResourcePatternResolver#doFindPathMatchingFileResources()
- PathMatchingResourcePatternResolver#findAllClassPathResources
通過classloader來加載資源目錄，代碼如下
protected Resource[] findAllClassPathResources(String location) throws IOException {
String path = location;
//例如com/question/
if (path.startsWith("/")) {
path = path.substring(1);
}
//真實查找方法
Set<Resource> result = doFindAllClassPathResources(path);
return result.toArray(new Resource[result.size()]);
}
進而看PathMatchingResourcePatternResolver#doFindAllClassPathResources()
protected Set<Resource> doFindAllClassPathResources(String path) throws IOException {
Set<Resource> result = new LinkedHashSet<Resource>(16);
ClassLoader cl = getClassLoader();
//通過classloader來加載資源目錄，這里也會去找尋classpath路徑下的jar包或者zip包
Enumeration<URL> resourceUrls = (cl != null ? cl.getResources(path) : ClassLoader.getSystemResources(path));
while (resourceUrls.hasMoreElements()) {
URL url = resourceUrls.nextElement();
//對找到的路徑保存為UrlResource對象放入set集合中
result.add(convertClassLoaderURL(url));
}
if ("".equals(path)) {
//加載jar協議的資源
addAllClassLoaderJarRoots(cl, result);
}
return result;
}
Note：一般而言找到的結果為一個，也就是file協議的項目工程資源目錄，不建議查找的base-package含有jar包的資源目錄，比如
org.springframework
- PathMatchingResourcePatternResolver#doFindPathMatchingFileResources()
查找指定目錄下的所有文件，這里特指class文件
protected Set<Resource> doFindPathMatchingFileResources(Resource rootDirResource, String subPattern)
throws IOException {
File rootDir;
try {
//獲取絕對路徑對應的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);
}
//異常則返回空的集合
return Collections.emptySet();
}
return doFindMatchingFileSystemResources(rootDir, subPattern);
}
進而看真實的查找方法doFindMatchingFileSystemResources()，代碼如下
protected Set<Resource> doFindMatchingFileSystemResources(File rootDir, String subPattern) throws IOException {
if (logger.isDebugEnabled()) {
logger.debug("Looking for matching resources in directory tree [" + rootDir.getPath() + "]");
}
//真實的調用方法
Set<File> matchingFiles = retrieveMatchingFiles(rootDir, subPattern);
Set<Resource> result = new LinkedHashSet<Resource>(matchingFiles.size());
for (File file : matchingFiles) {
//對查找到的資源包裝為FileSystemResource對象
result.add(new FileSystemResource(file));
}
return result;
}
繼續觀察真實加載文件資源的方法retriveMatchingFiles()，代碼如下
protected Set<File> retrieveMatchingFiles(File rootDir, String pattern) throws IOException {
//根目錄不存在？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();
}
//不是目錄？返回為空
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();
}
//不可讀？返回為空
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();
}
//轉換根目錄全路徑為標准的查找路徑
String fullPattern = StringUtils.replace(rootDir.getAbsolutePath(), File.separator, "/");
if (!pattern.startsWith("/")) {
fullPattern += "/";
}
//查找類型為.class文件
fullPattern = fullPattern + StringUtils.replace(pattern, File.separator, "/");
Set<File> result = new LinkedHashSet<File>(8);
doRetrieveMatchingFiles(fullPattern, rootDir, result);
return result;
}
接着瞧doRetriveMathingFiles的重載方法，代碼如下
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 + "]");
}
//從根目錄開始羅列文件集合
File[] dirContents = dir.listFiles();
if (dirContents == null) {
//查找到沒有了則直接返回
if (logger.isWarnEnabled()) {
logger.warn("Could not retrieve contents of directory [" + dir.getAbsolutePath() + "]");
}
return;
}
//遍歷
for (File content : dirContents) {
//獲取當前文件路徑
String currPath = StringUtils.replace(content.getAbsolutePath(), File.separator, "/");
//查找到的子文件仍是目錄且以根目錄為開頭
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 {
//遞歸調用查找所有的文件
doRetrieveMatchingFiles(fullPattern, content, result);
}
}
//查看當前文件路徑是否滿足**/*.class格式，滿足則添加
if (getPathMatcher().match(fullPattern, currPath)) {
result.add(content);
}
}
}
小結
classpath*:表示查找classpath路徑下的所有符合條件的資源，包含jar、zip等資源；classpath:表示優先在項目的資源目錄下查找，找不到才去jar、zip等資源中查找該類可以幫助spring查找到符合ant-style格式的所有資源，所以富有借鑒意義。附：ant-style指的是類似
*/?此類的匹配字符