1.统一资源接口的子类结构
WritableResource: 可写资源接口ByteArrayResource：二进制数组资源ClassPathResource：类路径下的资源，资源以相对路径的方式表示FileSystemResource：文件系统资源，资源以文件系统的方式表示如：D://data/beans.xmlServletContextPathResource：为访问Web容器上下文中的资源而设计的类，负责以相对于Web应用根目录的路径加载资源。它支持以流和URL的方式访问，在War解包的情况下，也可以通过File方式访问，。该类可以直接从JAR包中访问资源。PathResource：Path封装了java.net.URL、java.nio.file.Path、文件系统资源，它可以访问任何通过URL、Path、文件系统路径表示的资源，如文件系统资源、HTTP资源等。
2.统一资源Resource
Spring框架内使用的org.springframework.core.io.Resouce接口作为所有资源的抽象和访问接口。
public interface Resource extends InputStreamSource {
/**
* 判断资源文件是否存在
*/
boolean exists();
/**
* 资源文件是否可读
*/
default boolean isReadable() {
return exists();
}
/**
* 判断资源文件句柄是否被打开
*/
default boolean isOpen() {
return false;
}
/**
* 判定资源文件是否为File
*/
default boolean isFile() {
return false;
}
/**
* 返回资源文件的URL
*/
URL getURL() throws IOException;
/**
* 返回资源文件URI
*/
URI getURI() throws IOException;
/**
* 返回资源文件对象
*/
File getFile() throws IOException;
/**
* 返回 ReadableByteChannel nio channel访问
*/
default ReadableByteChannel readableChannel() throws IOException {
return Channels.newChannel(getInputStream());
}
/**
* 资源文件内容长度
*/
long contentLength() throws IOException;
/**
* 资源文件的上次修改时间
*/
long lastModified() throws IOException;
/**
*根据资源we年的相对路径创建新资源
*/
Resource createRelative(String relativePath) throws IOException;
/**
* 获取文件名称
*/
@Nullable
String getFilename();
/**
* 资源描述
*/
String getDescription();
}
Resource作为资源的统一抽象，定义了一些通用的方法，由子类AbstractResource提供了统一的默认实现，如果需要自定义拓展，可以直接继承此类。
public abstract class AbstractResource implements Resource {
/**
* 判断资源文件是否存在
*/
@Override
public boolean exists() {
try {
// 通过File文件方法判断文件是否存在
return getFile().exists();
}
catch (IOException ex) {
try {
// 基于InputStream判断文件是否存在
getInputStream().close();
return true;
}
catch (Throwable isEx) {
return false;
}
}
}
/**
* 资源文件是否可读
*/
@Override
public boolean isReadable() {
return exists();
}
/**
* 直接返回false 表示未打开
*/
@Override
public boolean isOpen() {
return false;
}
/**
* 直接返回false，表示不为File
*/
@Override
public boolean isFile() {
return false;
}
/**
* 直接抛出异常，由子类自定义覆盖实现
*/
@Override
public URL getURL() throws IOException {
throw new FileNotFoundException(getDescription() + " cannot be resolved to URL");
}
/**
* 基于getURL() 构建URI
*/
@Override
public URI getURI() throws IOException {
URL url = getURL();
try {
return ResourceUtils.toURI(url);
}
catch (URISyntaxException ex) {
throw new NestedIOException("Invalid URI [" + url + "]", ex);
}
}
/**
* 直接抛出异常，由子类实现
*/
@Override
public File getFile() throws IOException {
throw new FileNotFoundException(getDescription() + " cannot be resolved to absolute file path");
}
/**
* 根据InputStream构建ByteChannel
*/
@Override
public ReadableByteChannel readableChannel() throws IOException {
return Channels.newChannel(getInputStream());
}
/**
* 计算资源文件字节长度
*/
@Override
public long contentLength() throws IOException {
InputStream is = getInputStream();
try {
long size = 0;
byte[] buf = new byte[256];
int read;
while ((read = is.read(buf)) != -1) {
size += read;
}
return size;
}
finally {
try {
is.close();
}
catch (IOException ex) {
}
}
}
/**
* 获取文件最后一次修改时间 timestamp
*/
@Override
public long lastModified() throws IOException {
File fileToCheck = getFileForLastModifiedCheck();
long lastModified = fileToCheck.lastModified();
if (lastModified == 0L && !fileToCheck.exists()) {
throw new FileNotFoundException(getDescription() +
" cannot be resolved in the file system for checking its last-modified timestamp");
}
return lastModified;
}
/**
* 获取资源File（拿到要获取最后修改时间的资源File）
*/
protected File getFileForLastModifiedCheck() throws IOException {
return getFile();
}
/**
* 根据相对路径构造Resource，默认实现抛出 FileNotFoundException 异常，交个子类实现
*/
@Override
public Resource createRelative(String relativePath) throws IOException {
throw new FileNotFoundException("Cannot create a relative resource for " + getDescription());
}
/**
* 获取资源名称，默认返回null，交给子类实现
*/
@Override
@Nullable
public String getFilename() {
return null;
}
/**
* This implementation compares description strings.
* @see #getDescription()
*/
@Override
public boolean equals(Object other) {
return (this == other || (other instanceof Resource &&
((Resource) other).getDescription().equals(getDescription())));
}
/**
* This implementation returns the description's hash code.
* @see #getDescription()
*/
@Override
public int hashCode() {
return getDescription().hashCode();
}
/**
* This implementation returns the description of this resource.
* @see #getDescription()
* 返回资源描述
*/
@Override
public String toString() {
return getDescription();
}
}
3.资源加载器ResourceLoader结构体系
ResourcePatternResolver：是对ResourceLoader的拓展，根据资源文件location一次加载多个资源文件，返回一个Resource列表。PathMatchingResourcePatternResolver: 是ResourcePatternResolver的最常用的子类，除了支持"classpath*:"前缀外，还支持Ant锋哥的路径匹配模式（如：**/*.xml）。FileSystemResourceLoader：继承了DefaultResourceLoader并覆写了getResourceByPath()方法。该类主要增强了可以从文件系统加载资源并返回FileSystemResource。ClassRelativeResourceLoader：是类似于FileSystemResourceLoader，是DefaultResourceLoader的另一个子类 ，也是覆写了getResourceByPath()。该类主要增强了可以根据给定的Class所在的包或者包的子包下记载资源，返回的是ClassPathResource。
4.源码分析
4.1 资源定位：ResourceLoader
Spring将资源的定义和资源的加载区分开来，Resource定义了统一的资源，那资源加载则由ResourceLoader来统一加载。
public interface ResourceLoader {
/** Pseudo URL prefix for loading from the class path: "classpath:". */
String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;
/**
* Return a Resource handle for the specified resource location.
* 通过资源定位返回资源文件
* <p>The handle should always be a reusable resource descriptor,
* allowing for multiple {@link Resource#getInputStream()} calls.
* <p><ul>
* <li>Must support fully qualified URLs, e.g. "file:C:/test.dat".
* <li>Must support classpath pseudo-URLs, e.g. "classpath:test.dat".
* <li>Should support relative file paths, e.g. "WEB-INF/test.dat".
* (This will be implementation-specific, typically provided by an
* ApplicationContext implementation.)
* </ul>
* <p>Note that a Resource handle does not imply an existing resource;
* you need to invoke {@link Resource#exists} to check for existence.
* @param location the resource location
* @return a corresponding Resource handle (never {@code null})
* @see #CLASSPATH_URL_PREFIX
* @see Resource#exists()
* @see Resource#getInputStream()
*/
Resource getResource(String location);
/**
* Expose the ClassLoader used by this ResourceLoader.
* 返回资源加载器的类加载器
* <p>Clients which need to access the ClassLoader directly can do so
* in a uniform manner with the ResourceLoader, rather than relying
* on the thread context ClassLoader.
* @return the ClassLoader
* (only {@code null} if even the system ClassLoader isn't accessible)
* @see org.springframework.util.ClassUtils#getDefaultClassLoader()
* @see org.springframework.util.ClassUtils#forName(String, ClassLoader)
*/
@Nullable
ClassLoader getClassLoader();
}
ResourceLoader为Spring定义的统一资源加载接口。
4.2 资源加载器的默认实现：DefaultResourceLoader
public class DefaultResourceLoader implements ResourceLoader {
@Nullable
private ClassLoader classLoader;
private final Set<ProtocolResolver> protocolResolvers = new LinkedHashSet<>(4);
private final Map<Class<?>, Map<Resource, ?>> resourceCaches = new ConcurrentHashMap<>(4);
/**
* 无参构造函数
* <p>ClassLoader access will happen using the thread context class loader
*/
public DefaultResourceLoader() {
// 默认使用thread context class loader
this.classLoader = ClassUtils.getDefaultClassLoader();
}
/**
* 可以手动设置类加载器
* @param classLoader the ClassLoader to load class path resources with, or {@code null}
* for using the thread context class loader at the time of actual resource access
*/
public DefaultResourceLoader(@Nullable ClassLoader classLoader) {
this.classLoader = classLoader;
}
/**
* Specify the ClassLoader to load class path resources with, or {@code null}
* for using the thread context class loader at the time of actual resource access.
* <p>The default is that ClassLoader access will happen using the thread context
* class loader at the time of this ResourceLoader's initialization.
*/
public void setClassLoader(@Nullable ClassLoader classLoader) {
this.classLoader = classLoader;
}
/**
* Return the ClassLoader to load class path resources with.
*/
@Override
@Nullable
public ClassLoader getClassLoader() {
return (this.classLoader != null ? this.classLoader : ClassUtils.getDefaultClassLoader());
}
/**
* 这里是设置用自定义的资源加载协议，是DefaultResourceLoaderde的SPI
* 允许用户自定义加载协议美不需要集成ResourceLoader的子类
* 用户自定义加载资源协议需要自定义实现ProtocolResolver接口，实现resolve方法，然后在此处添加到加载协议
* Register the given resolver with this resource loader, allowing for
* additional protocols to be handled.
* <p>Any such resolver will be invoked ahead of this loader's standard
* resolution rules. It may therefore also override any default rules.
* @since 4.3
* @see #getProtocolResolvers()
*/
public void addProtocolResolver(ProtocolResolver resolver) {
Assert.notNull(resolver, "ProtocolResolver must not be null");
this.protocolResolvers.add(resolver);
}
/**
* 返回自定义的加载协议集合
* Return the collection of currently registered protocol resolvers,
* allowing for introspection as well as modification.
* @since 4.3
*/
public Collection<ProtocolResolver> getProtocolResolvers() {
return this.protocolResolvers;
}
/**
* Obtain a cache for the given value type, keyed by {@link Resource}.
* @param valueType the value type, e.g. an ASM {@code MetadataReader}
* @return the cache {@link Map}, shared at the {@code ResourceLoader} level
* @since 5.0
*/
@SuppressWarnings("unchecked")
public <T> Map<Resource, T> getResourceCache(Class<T> valueType) {
return (Map<Resource, T>) this.resourceCaches.computeIfAbsent(valueType, key -> new ConcurrentHashMap<>());
}
/**
* Clear all resource caches in this resource loader.
* @since 5.0
* @see #getResourceCache
*/
public void clearResourceCaches() {
this.resourceCaches.clear();
}
// 资源加载的核心方法
@Override
public Resource getResource(String location) {
Assert.notNull(location, "Location must not be null");
// 首先遍历自定义的资源加载协议加载资源
for (ProtocolResolver protocolResolver : getProtocolResolvers()) {
Resource resource = protocolResolver.resolve(location, this);
if (resource != null) {
return resource;
}
}
// 以 / 开头的，执行返回ClassPathContextResource类型的资源
if (location.startsWith("/")) {
return getResourceByPath(location);
}
// 如果是classpath: 开头的，返回ClassPathResource类型的资源
else if (location.startsWith(CLASSPATH_URL_PREFIX)) {
return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
}
// 然后根据是否为文件URL，是返回FileUrlResource类型的资源，否反回UrlResource类型的资源
else {
try {
// Try to parse the location as a URL...
URL url = new URL(location);
return (ResourceUtils.isFileURL(url) ? new FileUrlResource(url) : new UrlResource(url));
}
catch (MalformedURLException ex) {
// No URL -> resolve as resource path.
// 最后，返回 ClassPathContextResource 类型的资源
return getResourceByPath(location);
}
}
}
/**
* Return a Resource handle for the resource at the given path.
* <p>The default implementation supports class path locations. This should
* be appropriate for standalone implementations but can be overridden,
* e.g. for implementations targeted at a Servlet container.
* @param path the path to the resource
* @return the corresponding Resource handle
* @see ClassPathResource
* @see org.springframework.context.support.FileSystemXmlApplicationContext#getResourceByPath
* @see org.springframework.web.context.support.XmlWebApplicationContext#getResourceByPath
*/
protected Resource getResourceByPath(String path) {
return new ClassPathContextResource(path, getClassLoader());
}
/**
* ClassPathResource that explicitly expresses a context-relative path
* through implementing the ContextResource interface.
*/
protected static class ClassPathContextResource extends ClassPathResource implements ContextResource {
public ClassPathContextResource(String path, @Nullable ClassLoader classLoader) {
super(path, classLoader);
}
@Override
public String getPathWithinContext() {
return getPath();
}
@Override
public Resource createRelative(String relativePath) {
String pathToUse = StringUtils.applyRelativePath(getPath(), relativePath);
return new ClassPathContextResource(pathToUse, getClassLoader());
}
}
}
4.2 文件系统资源加载器： FileSystemResourceLoader
public class FileSystemResourceLoader extends DefaultResourceLoader {
/**
* 根据文件路径获取 FileSystemResource->FileSystemContextResource是其子类
* Resolve resource paths as file system paths.
* <p>Note: Even if a given path starts with a slash, it will get
* interpreted as relative to the current VM working directory.
* @param path the path to the resource
* @return the corresponding Resource handle
* @see FileSystemResource
* @see org.springframework.web.context.support.ServletContextResourceLoader#getResourceByPath
*/
@Override
protected Resource getResourceByPath(String path) {
if (path.startsWith("/")) {
path = path.substring(1);
}
return new FileSystemContextResource(path);
}
/**
* 内部类主要是要实现ContextResource实现getPathWithinContext()方法
* FileSystemResource that explicitly expresses a context-relative path
* through implementing the ContextResource interface.
*/
private static class FileSystemContextResource extends FileSystemResource implements ContextResource {
public FileSystemContextResource(String path) {
super(path);
}
@Override
public String getPathWithinContext() {
return getPath();
}
}
}
4.4 ClassPath的资源加载器：ClassRelativeResourceLoader
public class ClassRelativeResourceLoader extends DefaultResourceLoader {
// 主要用户标识从哪个class路径下加载资源
private final Class<?> clazz;
/**
* Create a new ClassRelativeResourceLoader for the given class.
* @param clazz the class to load resources through
*/
public ClassRelativeResourceLoader(Class<?> clazz) {
Assert.notNull(clazz, "Class must not be null");
this.clazz = clazz;
setClassLoader(clazz.getClassLoader());
}
// 核心方法，返回ClassPathResource
@Override
protected Resource getResourceByPath(String path) {
// 根据给定的class所在包或者所在包的子包下加载资源
return new ClassRelativeContextResource(path, this.clazz);
}
/**
* ClassPathResource that explicitly expresses a context-relative path
* through implementing the ContextResource interface.
*/
private static class ClassRelativeContextResource extends ClassPathResource implements ContextResource {
private final Class<?> clazz;
public ClassRelativeContextResource(String path, Class<?> clazz) {
super(path, clazz);
this.clazz = clazz;
}
@Override
public String getPathWithinContext() {
return getPath();
}
@Override
public Resource createRelative(String relativePath) {
String pathToUse = StringUtils.applyRelativePath(getPath(), relativePath);
return new ClassRelativeContextResource(pathToUse, this.clazz);
}
}
}
4.5 加载多个资源：ResourcePatternResolver
// 主要是对ResourceLoader的增强，支持加载多个资源
public interface ResourcePatternResolver extends ResourceLoader {
/**
* Pseudo URL prefix for all matching resources from the class path: "classpath*:"
* This differs from ResourceLoader's classpath URL prefix in that it
* retrieves all matching resources for a given name (e.g. "/beans.xml"),
* for example in the root of all deployed JAR files.
* @see org.springframework.core.io.ResourceLoader#CLASSPATH_URL_PREFIX
*/
String CLASSPATH_ALL_URL_PREFIX = "classpath*:";
/**
* 根据指定路径，返回加载的多个资源
* Resolve the given location pattern into Resource objects.
* <p>Overlapping resource entries that point to the same physical
* resource should be avoided, as far as possible. The result should
* have set semantics.
* @param locationPattern the location pattern to resolve
* @return the corresponding Resource objects
* @throws IOException in case of I/O errors
*/
Resource[] getResources(String locationPattern) throws IOException;
}
4.6 多个资源加载拓展（支持Ant）：PathMatchingResourcePatternResolver
public class PathMatchingResourcePatternResolver implements ResourcePatternResolver {
private static final Log logger = LogFactory.getLog(PathMatchingResourcePatternResolver.class);
@Nullable
private static Method equinoxResolveMethod;
static {
try {
// Detect Equinox OSGi (e.g. on WebSphere 6.1)
Class<?> fileLocatorClass = ClassUtils.forName("org.eclipse.core.runtime.FileLocator",
PathMatchingResourcePatternResolver.class.getClassLoader());
equinoxResolveMethod = fileLocatorClass.getMethod("resolve", URL.class);
logger.trace("Found Equinox FileLocator for OSGi bundle URL resolution");
}
catch (Throwable ex) {
equinoxResolveMethod = null;
}
}
private final ResourceLoader resourceLoader;
// Ant路径匹配器
private PathMatcher pathMatcher = new AntPathMatcher();
/**
* 默认创建采用默认的资源加载器
* Create a new PathMatchingResourcePatternResolver with a DefaultResourceLoader.
* <p>ClassLoader access will happen via the thread context class loader.
* @see org.springframework.core.io.DefaultResourceLoader
*/
public PathMatchingResourcePatternResolver() {
this.resourceLoader = new DefaultResourceLoader();
}
/**
* 可以指定资源加载器创建
* Create a new PathMatchingResourcePatternResolver.
* <p>ClassLoader access will happen via the thread context class loader.
* @param resourceLoader the ResourceLoader to load root directories and
* actual resources with
*/
public PathMatchingResourcePatternResolver(ResourceLoader resourceLoader) {
Assert.notNull(resourceLoader, "ResourceLoader must not be null");
this.resourceLoader = resourceLoader;
}
/**
* 指定classLoader
* Create a new PathMatchingResourcePatternResolver with a DefaultResourceLoader.
* @param classLoader the ClassLoader to load classpath resources with,
* or {@code null} for using the thread context class loader
* at the time of actual resource access
* @see org.springframework.core.io.DefaultResourceLoader
*/
public PathMatchingResourcePatternResolver(@Nullable ClassLoader classLoader) {
this.resourceLoader = new DefaultResourceLoader(classLoader);
}
/**
* Return the ResourceLoader that this pattern resolver works with.
*/
public ResourceLoader getResourceLoader() {
return this.resourceLoader;
}
@Override
@Nullable
public ClassLoader getClassLoader() {
return getResourceLoader().getClassLoader();
}
/**
* Set the PathMatcher implementation to use for this
* resource pattern resolver. Default is AntPathMatcher.
* @see org.springframework.util.AntPathMatcher
*/
public void setPathMatcher(PathMatcher pathMatcher) {
Assert.notNull(pathMatcher, "PathMatcher must not be null");
this.pathMatcher = pathMatcher;
}
/**
* Return the PathMatcher that this resource pattern resolver uses.
*/
public PathMatcher getPathMatcher() {
return this.pathMatcher;
}
// 委托给资源加载器加载资源
@Override
public Resource getResource(String location) {
return getResourceLoader().getResource(location);
}
// 资源加载的核心方法
@Override
public Resource[] getResources(String locationPattern) throws IOException {
Assert.notNull(locationPattern, "Location pattern must not be null");
// 如果是"classpath*:" 开头
if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {
// 路径包含通配符（即判断是否含有*或者?），解析通配符并加载资源文件
// a class path resource (multiple resources for same name possible)
if (getPathMatcher().isPattern(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()))) {
// 解析通配符文件路径获取根目录
// a class path resource pattern
return findPathMatchingResources(locationPattern);
}
// 路径不包含ant通配符，直接交给ResourceLoader来实现
else {
// all class path resources with the given name
return findAllClassPathResources(locationPattern.substring(CLASSPATH_ALL_URL_PREFIX.length()));
}
}
// 不以 "classpath*:" 开头
else {
// 通常
// Generally only look for a pattern after a prefix here,
// and on Tomcat only after the "*/" separator for its "war:" protocol.
int prefixEnd = (locationPattern.startsWith("war:") ? locationPattern.indexOf("*/") + 1 :
locationPattern.indexOf(':') + 1);
// 路径包含通配符
if (getPathMatcher().isPattern(locationPattern.substring(prefixEnd))) {
// a file pattern
return findPathMatchingResources(locationPattern);
}
// 路径不包含通配符
else {
//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
// a single resource with the given name
return new Resource[] {getResourceLoader().getResource(locationPattern)};
}
}
}
/**
* Find all class location resources with the given location via the ClassLoader.
* Delegates to {@link #doFindAllClassPathResources(String)}.
* @param location the absolute path within the classpath
* @return the result as Resource array
* @throws IOException in case of I/O errors
* @see java.lang.ClassLoader#getResources
* @see #convertClassLoaderURL
*/
protected Resource[] findAllClassPathResources(String location) throws IOException {
String path = location;
if (path.startsWith("/")) {
path = path.substring(1);
}
Set<Resource> result = doFindAllClassPathResources(path);
if (logger.isTraceEnabled()) {
logger.trace("Resolved classpath location [" + location + "] to resources " + result);
}
return result.toArray(new Resource[0]);
}
/**
* Find all class location resources with the given path via the ClassLoader.
* Called by {@link #findAllClassPathResources(String)}.
* @param path the absolute path within the classpath (never a leading slash)
* @return a mutable Set of matching Resource instances
* @since 4.1.1
*/
protected Set<Resource> doFindAllClassPathResources(String path) throws IOException {
Set<Resource> 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<URL> 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
// The above result is likely to be incomplete, i.e. only containing file system references.
// We need to have pointers to each of the jar files on the classpath as well...
addAllClassLoaderJarRoots(cl, result);
}
return result;
}
/**
* Convert the given URL as returned from the ClassLoader into a {@link Resource}.
* <p>The default implementation simply creates a {@link UrlResource} instance.
* @param url a URL as returned from the ClassLoader
* @return the corresponding Resource object
* @see java.lang.ClassLoader#getResources
* @see org.springframework.core.io.Resource
*/
protected Resource convertClassLoaderURL(URL url) {
return new UrlResource(url);
}
/**
* Search all {@link URLClassLoader} URLs for jar file references and add them to the
* given set of resources in the form of pointers to the root of the jar file content.
* @param classLoader the ClassLoader to search (including its ancestors)
* @param result the set of resources to add jar roots to
* @since 4.1.1
*/
protected void addAllClassLoaderJarRoots(@Nullable ClassLoader classLoader, Set<Resource> result) {
if (classLoader instanceof URLClassLoader) {
try {
for (URL url : ((URLClassLoader) classLoader).getURLs()) {
try {
UrlResource jarResource = (ResourceUtils.URL_PROTOCOL_JAR.equals(url.getProtocol()) ?
new UrlResource(url) :
new UrlResource(ResourceUtils.JAR_URL_PREFIX + url + ResourceUtils.JAR_URL_SEPARATOR));
if (jarResource.exists()) {
result.add(jarResource);
}
}
catch (MalformedURLException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Cannot search for matching files underneath [" + url +
"] because it cannot be converted to a valid 'jar:' URL: " + ex.getMessage());
}
}
}
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Cannot introspect jar files since ClassLoader [" + classLoader +
"] does not support 'getURLs()': " + ex);
}
}
}
if (classLoader == ClassLoader.getSystemClassLoader()) {
// "java.class.path" manifest evaluation...
addClassPathManifestEntries(result);
}
if (classLoader != null) {
try {
// Hierarchy traversal...
addAllClassLoaderJarRoots(classLoader.getParent(), result);
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Cannot introspect jar files in parent ClassLoader since [" + classLoader +
"] does not support 'getParent()': " + ex);
}
}
}
}
/**
* Determine jar file references from the "java.class.path." manifest property and add them
* to the given set of resources in the form of pointers to the root of the jar file content.
* @param result the set of resources to add jar roots to
* @since 4.3
*/
protected void addClassPathManifestEntries(Set<Resource> result) {
try {
String javaClassPathProperty = System.getProperty("java.class.path");
for (String path : StringUtils.delimitedListToStringArray(
javaClassPathProperty, System.getProperty("path.separator"))) {
try {
String filePath = new File(path).getAbsolutePath();
int prefixIndex = filePath.indexOf(':');
if (prefixIndex == 1) {
// Possibly "c:" drive prefix on Windows, to be upper-cased for proper duplicate detection
filePath = StringUtils.capitalize(filePath);
}
UrlResource jarResource = new UrlResource(ResourceUtils.JAR_URL_PREFIX +
ResourceUtils.FILE_URL_PREFIX + filePath + ResourceUtils.JAR_URL_SEPARATOR);
// Potentially overlapping with URLClassLoader.getURLs() result above!
if (!result.contains(jarResource) && !hasDuplicate(filePath, result) && jarResource.exists()) {
result.add(jarResource);
}
}
catch (MalformedURLException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Cannot search for matching files underneath [" + path +
"] because it cannot be converted to a valid 'jar:' URL: " + ex.getMessage());
}
}
}
}
catch (Exception ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to evaluate 'java.class.path' manifest entries: " + ex);
}
}
}
/**
* Check whether the given file path has a duplicate but differently structured entry
* in the existing result, i.e. with or without a leading slash.
* @param filePath the file path (with or without a leading slash)
* @param result the current result
* @return {@code true} if there is a duplicate (i.e. to ignore the given file path),
* {@code false} to proceed with adding a corresponding resource to the current result
*/
private boolean hasDuplicate(String filePath, Set<Resource> result) {
if (result.isEmpty()) {
return false;
}
String duplicatePath = (filePath.startsWith("/") ? filePath.substring(1) : "/" + filePath);
try {
return result.contains(new UrlResource(ResourceUtils.JAR_URL_PREFIX + ResourceUtils.FILE_URL_PREFIX +
duplicatePath + ResourceUtils.JAR_URL_SEPARATOR));
}
catch (MalformedURLException ex) {
// Ignore: just for testing against duplicate.
return false;
}
}
/**
* 查找指定路径下的所有资源，支持zip和jar中资源的查找
* Find all resources that match the given location pattern via the
* Ant-style PathMatcher. Supports resources in jar files and zip files
* and in the file system.
* @param locationPattern the location pattern to match
* @return the result as Resource array
* @throws IOException in case of I/O errors
* @see #doFindPathMatchingJarResources
* @see #doFindPathMatchingFileResources
* @see org.springframework.util.PathMatcher
*/
protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {
// 首先定位跟目录的路径，例如classpath*:com/test/
String rootDirPath = determineRootDir(locationPattern);
// 截取除了根路径的其他的匹配信息
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<Resource> 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
URL rootDirUrl = rootDirResource.getURL();
if (equinoxResolveMethod != null && rootDirUrl.getProtocol().startsWith("bundle")) {
URL resolvedUrl = (URL) ReflectionUtils.invokeMethod(equinoxResolveMethod, null, rootDirUrl);
if (resolvedUrl != null) {
rootDirUrl = resolvedUrl;
}
rootDirResource = new UrlResource(rootDirUrl);
}
if (rootDirUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirUrl, subPattern, getPathMatcher()));
}
// jar协议、zip协议、wsjar协议、vfszip协议
else if (ResourceUtils.isJarURL(rootDirUrl) || isJarResource(rootDirResource)) {
// 从jar包中找寻相应的所有class文件
result.addAll(doFindPathMatchingJarResources(rootDirResource, rootDirUrl, subPattern));
}
else {
//加载非jar、zip包的项目资源
result.addAll(doFindPathMatchingFileResources(rootDirResource, subPattern));
}
}
if (logger.isTraceEnabled()) {
logger.trace("Resolved location pattern [" + locationPattern + "] to resources " + result);
}
return result.toArray(new Resource[0]);
}
/**
* Determine the root directory for the given location.
* <p>Used for determining the starting point for file matching,
* resolving the root directory location to a {@code java.io.File}
* and passing it into {@code retrieveMatchingFiles}, with the
* remainder of the location as pattern.
* <p>Will return "/WEB-INF/" for the pattern "/WEB-INF/*.xml",
* for example.
* @param location the location to check
* @return the part of the location that denotes the root directory
* @see #retrieveMatchingFiles
*/
protected String determineRootDir(String location) {
int prefixEnd = location.indexOf(':') + 1;
int rootDirEnd = location.length();
while (rootDirEnd > prefixEnd && getPathMatcher().isPattern(location.substring(prefixEnd, rootDirEnd))) {
rootDirEnd = location.lastIndexOf('/', rootDirEnd - 2) + 1;
}
if (rootDirEnd == 0) {
rootDirEnd = prefixEnd;
}
return location.substring(0, rootDirEnd);
}
/**
* Resolve the specified resource for path matching.
* <p>By default, Equinox OSGi "bundleresource:" / "bundleentry:" URL will be
* resolved into a standard jar file URL that be traversed using Spring's
* standard jar file traversal algorithm. For any preceding custom resolution,
* override this method and replace the resource handle accordingly.
* @param original the resource to resolve
* @return the resolved resource (may be identical to the passed-in resource)
* @throws IOException in case of resolution failure
*/
protected Resource resolveRootDirResource(Resource original) throws IOException {
return original;
}
/**
* Return whether the given resource handle indicates a jar resource
* that the {@code doFindPathMatchingJarResources} method can handle.
* <p>By default, the URL protocols "jar", "zip", "vfszip and "wsjar"
* will be treated as jar resources. This template method allows for
* detecting further kinds of jar-like resources, e.g. through
* {@code instanceof} checks on the resource handle type.
* @param resource the resource handle to check
* (usually the root directory to start path matching from)
* @see #doFindPathMatchingJarResources
* @see org.springframework.util.ResourceUtils#isJarURL
*/
protected boolean isJarResource(Resource resource) throws IOException {
return false;
}
/**
* Find all resources in jar files that match the given location pattern
* via the Ant-style PathMatcher.
* @param rootDirResource the root directory as Resource
* @param rootDirURL the pre-resolved root directory URL
* @param subPattern the sub pattern to match (below the root directory)
* @return a mutable Set of matching Resource instances
* @throws IOException in case of I/O errors
* @since 4.3
* @see java.net.JarURLConnection
* @see org.springframework.util.PathMatcher
*/
protected Set<Resource> doFindPathMatchingJarResources(Resource rootDirResource, URL rootDirURL, String subPattern)
throws IOException {
URLConnection con = rootDirURL.openConnection();
JarFile jarFile;
String jarFileUrl;
String rootEntryPath;
boolean closeJarFile;
if (con instanceof JarURLConnection) {
// Should usually be the case for traditional JAR files.
JarURLConnection jarCon = (JarURLConnection) con;
ResourceUtils.useCachesIfNecessary(jarCon);
jarFile = jarCon.getJarFile();
jarFileUrl = jarCon.getJarFileURL().toExternalForm();
JarEntry jarEntry = jarCon.getJarEntry();
rootEntryPath = (jarEntry != null ? jarEntry.getName() : "");
closeJarFile = !jarCon.getUseCaches();
}
else {
// No JarURLConnection -> need to resort to URL file parsing.
// We'll assume URLs of the format "jar:path!/entry", with the protocol
// being arbitrary as long as following the entry format.
// We'll also handle paths with and without leading "file:" prefix.
String urlFile = rootDirURL.getFile();
try {
int separatorIndex = urlFile.indexOf(ResourceUtils.WAR_URL_SEPARATOR);
if (separatorIndex == -1) {
separatorIndex = urlFile.indexOf(ResourceUtils.JAR_URL_SEPARATOR);
}
if (separatorIndex != -1) {
jarFileUrl = urlFile.substring(0, separatorIndex);
rootEntryPath = urlFile.substring(separatorIndex + 2); // both separators are 2 chars
jarFile = getJarFile(jarFileUrl);
}
else {
jarFile = new JarFile(urlFile);
jarFileUrl = urlFile;
rootEntryPath = "";
}
closeJarFile = true;
}
catch (ZipException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Skipping invalid jar classpath entry [" + urlFile + "]");
}
return Collections.emptySet();
}
}
try {
if (logger.isTraceEnabled()) {
logger.trace("Looking for matching resources in jar file [" + jarFileUrl + "]");
}
if (!"".equals(rootEntryPath) && !rootEntryPath.endsWith("/")) {
// Root entry path must end with slash to allow for proper matching.
// The Sun JRE does not return a slash here, but BEA JRockit does.
rootEntryPath = rootEntryPath + "/";
}
Set<Resource> result = new LinkedHashSet<>(8);
for (Enumeration<JarEntry> entries = jarFile.entries(); entries.hasMoreElements();) {
JarEntry entry = entries.nextElement();
String entryPath = entry.getName();
if (entryPath.startsWith(rootEntryPath)) {
String relativePath = entryPath.substring(rootEntryPath.length());
if (getPathMatcher().match(subPattern, relativePath)) {
result.add(rootDirResource.createRelative(relativePath));
}
}
}
return result;
}
finally {
if (closeJarFile) {
jarFile.close();
}
}
}
/**
* Resolve the given jar file URL into a JarFile object.
*/
protected JarFile getJarFile(String jarFileUrl) throws IOException {
if (jarFileUrl.startsWith(ResourceUtils.FILE_URL_PREFIX)) {
try {
return new JarFile(ResourceUtils.toURI(jarFileUrl).getSchemeSpecificPart());
}
catch (URISyntaxException ex) {
// Fallback for URLs that are not valid URIs (should hardly ever happen).
return new JarFile(jarFileUrl.substring(ResourceUtils.FILE_URL_PREFIX.length()));
}
}
else {
return new JarFile(jarFileUrl);
}
}
/**
* Find all resources in the file system that match the given location pattern
* via the Ant-style PathMatcher.
* @param rootDirResource the root directory as Resource
* @param subPattern the sub pattern to match (below the root directory)
* @return a mutable Set of matching Resource instances
* @throws IOException in case of I/O errors
* @see #retrieveMatchingFiles
* @see org.springframework.util.PathMatcher
*/
protected Set<Resource> 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 (FileNotFoundException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Cannot search for matching files underneath " + rootDirResource +
" in the file system: " + ex.getMessage());
}
return Collections.emptySet();
}
catch (Exception ex) {
if (logger.isInfoEnabled()) {
logger.info("Failed to resolve " + rootDirResource + " in the file system: " + ex);
}
// 异常则返回空的集合
return Collections.emptySet();
}
return doFindMatchingFileSystemResources(rootDir, subPattern);
}
/**
* Find all resources in the file system that match the given location pattern
* via the Ant-style PathMatcher.
* @param rootDir the root directory in the file system
* @param subPattern the sub pattern to match (below the root directory)
* @return a mutable Set of matching Resource instances
* @throws IOException in case of I/O errors
* @see #retrieveMatchingFiles
* @see org.springframework.util.PathMatcher
*/
protected Set<Resource> doFindMatchingFileSystemResources(File rootDir, String subPattern) throws IOException {
if (logger.isTraceEnabled()) {
logger.trace("Looking for matching resources in directory tree [" + rootDir.getPath() + "]");
}
//真实的调用方法
Set<File> matchingFiles = retrieveMatchingFiles(rootDir, subPattern);
Set<Resource> 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;
}
/**
* Retrieve files that match the given path pattern,
* checking the given directory and its subdirectories.
* @param rootDir the directory to start from
* @param pattern the pattern to match against,
* relative to the root directory
* @return a mutable Set of matching Resource instances
* @throws IOException if directory contents could not be retrieved
*/
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");
}
//根目录不存在？返回空集合
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.isInfoEnabled()) {
logger.info("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.isInfoEnabled()) {
logger.info("Skipping 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<File> result = new LinkedHashSet<>(8);
doRetrieveMatchingFiles(fullPattern, rootDir, result);
return result;
}
/**
* Recursively retrieve files that match the given pattern,
* adding them to the given result list.
* @param fullPattern the pattern to match against,
* with prepended root directory path
* @param dir the current directory
* @param result the Set of matching File instances to add to
* @throws IOException if directory contents could not be retrieved
*/
protected void doRetrieveMatchingFiles(String fullPattern, File dir, Set<File> result) throws IOException {
if (logger.isTraceEnabled()) {
logger.trace("Searching directory [" + dir.getAbsolutePath() +
"] for files matching pattern [" + fullPattern + "]");
}
//从根目录开始罗列文件集合
for (File content : listDirectory(dir)) {
//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);
}
}
}
/**
* Determine a sorted list of files in the given directory.
* @param dir the directory to introspect
* @return the sorted list of files (by default in alphabetical order)
* @since 5.1
* @see File#listFiles()
*/
protected File[] listDirectory(File dir) {
File[] files = dir.listFiles();
if (files == null) {
if (logger.isInfoEnabled()) {
logger.info("Could not retrieve contents of directory [" + dir.getAbsolutePath() + "]");
}
return new File[0];
}
Arrays.sort(files, Comparator.comparing(File::getName));
return files;
}
/**
* Inner delegate class, avoiding a hard JBoss VFS API dependency at runtime.
*/
private static class VfsResourceMatchingDelegate {
public static Set<Resource> findMatchingResources(
URL rootDirURL, String locationPattern, PathMatcher pathMatcher) throws IOException {
Object root = VfsPatternUtils.findRoot(rootDirURL);
PatternVirtualFileVisitor visitor =
new PatternVirtualFileVisitor(VfsPatternUtils.getPath(root), locationPattern, pathMatcher);
VfsPatternUtils.visit(root, visitor);
return visitor.getResources();
}
}
/**
* VFS visitor for path matching purposes.
*/
@SuppressWarnings("unused")
private static class PatternVirtualFileVisitor implements InvocationHandler {
private final String subPattern;
private final PathMatcher pathMatcher;
private final String rootPath;
private final Set<Resource> resources = new LinkedHashSet<>();
public PatternVirtualFileVisitor(String rootPath, String subPattern, PathMatcher pathMatcher) {
this.subPattern = subPattern;
this.pathMatcher = pathMatcher;
this.rootPath = (rootPath.isEmpty() || rootPath.endsWith("/") ? rootPath : rootPath + "/");
}
@Override
@Nullable
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
if (Object.class == method.getDeclaringClass()) {
if (methodName.equals("equals")) {
// Only consider equal when proxies are identical.
return (proxy == args[0]);
}
else if (methodName.equals("hashCode")) {
return System.identityHashCode(proxy);
}
}
else if ("getAttributes".equals(methodName)) {
return getAttributes();
}
else if ("visit".equals(methodName)) {
visit(args[0]);
return null;
}
else if ("toString".equals(methodName)) {
return toString();
}
throw new IllegalStateException("Unexpected method invocation: " + method);
}
public void visit(Object vfsResource) {
if (this.pathMatcher.match(this.subPattern,
VfsPatternUtils.getPath(vfsResource).substring(this.rootPath.length()))) {
this.resources.add(new VfsResource(vfsResource));
}
}
@Nullable
public Object getAttributes() {
return VfsPatternUtils.getVisitorAttributes();
}
public Set<Resource> getResources() {
return this.resources;
}
public int size() {
return this.resources.size();
}
@Override
public String toString() {
return "sub-pattern: " + this.subPattern + ", resources: " + this.resources;
}
}
}
总结：
- Spring 提供了Resource和ResourceLoader来统一抽象整个资源和资源定位，是的资源和资源定位有更加清晰的界线，并且提供了合适的Default实现类，供用户自定义拓展使用，使结构更加容易拓展和使用
AbstractResource提供了Resource的默认抽象实现，子类只需要继承覆盖相应的方法即可，对于自定义实现Resource方便快捷。DefaultResourceLoader提供了ResourceLoader``的默认实现，并且开放了自定义协议记载资源文件的接口ProtocolResolver`。
本文重点讲解资源定位和资源加载的整体流程，具体细节没有涉及太多，如果感兴趣，可以自行查看源代码。
