我们平时使用spring框架的时候经常需要引入一些配置文件，如.propertis文件。其实有号和没有星号的区别不是很大，但有细微区别，这里我结合spring的源码简要分析有号和没有*号的的区别，有误的地方请指出。
classparth:只会从第一个classpath中加载，而classpath*:会从所有的classpath中加载如果要加载的资源，不在当前ClassLoader的路径里，那么如果用classpath:打头前缀是找不到的，这种情况下就需要使用classpath*:前缀；另一种情况下，在多个classpath中存在同名资源，都需要加载，那么用classpath:只会加载第一个，这种情况下也需要用classpath*:前缀。可想而知，用classpath*:需要遍历所有的classpath，所以加载速度较classpath慢，因此，在规划的时候，应该尽可能规划好资源文件所在的路径，尽量避免使用classpath*。
现在我们分析一下classpath 与 classpath*以及通配符spring是怎么处理的。
首先需要知道spring解析文件路径主要是spring-core-xxxxx.jar\org\springframework\core\io包及其子包完成的。先看InputStreamSource
在Spring中，定义了接口InputStreamSource，这个类中只包含一个方法：
public interface InputStreamSource {
/**
* Return an {@link InputStream}.
* <p>It is expected that each call creates a <i>fresh</i> stream.
* <p>This requirement is particularly important when you consider an API such
* as JavaMail, which needs to be able to read the stream multiple times when
* creating mail attachments. For such a use case, it is <i>required</i>
* that each {@code getInputStream()} call returns a fresh stream.
* @return the input stream for the underlying resource (must not be {@code null})
* @throws IOException if the stream could not be opened
* @see org.springframework.mail.javamail.MimeMessageHelper#addAttachment(String, InputStreamSource)
*/
InputStream getInputStream() throws IOException;
}
InputStreamSource下面有一个Resource子接口，重要的方法有几个：
/**
* Return whether this resource actually exists in physical form.
*
This method performs a definitive existence check, whereas the
* existence of a {@code Resource} handle only guarantees a
* valid descriptor handle.
*/
boolean exists();
/**
* Return whether the contents of this resource can be read,
* e.g. via {@link #getInputStream()} or {@link #getFile()}.
* <p>Will be {@code true} for typical resource descriptors;
* note that actual content reading may still fail when attempted.
* However, a value of {@code false} is a definitive indication
* that the resource content cannot be read.
* @see #getInputStream()
*/
boolean isReadable();
/**
* Return whether this resource represents a handle with an open
* stream. If true, the InputStream cannot be read multiple times,
* and must be read and closed to avoid resource leaks.
* <p>Will be {@code false} for typical resource descriptors.
*/
boolean isOpen();
而Spring加载Resource文件是通过ResourceLoader来进行的，ResourceLoader接口只提供了classpath前缀的支持。
/* Pseudo URL prefix for loading from the class path: “classpath:” /
String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;
而classpath*的前缀支持是在它的子接口ResourcePatternResolver中。
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*:";
……………….
}
ResourcePatternResolver有一个实现类：PathMatchingResourcePatternResolver,现在我们看看PathMatchingResourcePatternResolver的getResources()方法，
@Override
public Resource[] getResources(String locationPattern) throws IOException {
Assert.notNull(locationPattern, "Location pattern must not be null");
//CLASSPATH_ALL_URL_PREFIX对应classpath*:
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()))) {
// 包含通配符
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 {
// 不以classpath*开头，且路径不包含通配符的就以这个方式处理；
return new Resource[] {getResourceLoader().getResource(locationPattern)};
}
}
}
由此可以看出以classpath*开头，包含通配符的就调用findAllClassPathResources（….）处理，
protected Resource[] findAllClassPathResources(String location) throws IOException {
String path = location;
if (path.startsWith(“/”)) {
path = path.substring(1);
}
Set result = doFindAllClassPathResources(path);
return result.toArray(new Resource[result.size()]);
}
protected Set<Resource> doFindAllClassPathResources(String path) throws IOException {
Set<Resource> result = new LinkedHashSet<Resource>(16);
ClassLoader cl = getClassLoader();
Enumeration<URL> resourceUrls = (cl != null ? cl.getResources(path) : ClassLoader.getSystemResources(path));
while (resourceUrls.hasMoreElements()) {
URL url = resourceUrls.nextElement();
result.add(convertClassLoaderURL(url));
}
if ("".equals(path)) {
// 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
*/
protected void addAllClassLoaderJarRoots(ClassLoader classLoader, Set<Resource> result) {
if (classLoader instanceof URLClassLoader) {
try {
for (URL url : ((URLClassLoader) classLoader).getURLs()) {
if (ResourceUtils.isJarFileURL(url)) {
try {
UrlResource jarResource = new UrlResource(
ResourceUtils.JAR_URL_PREFIX + url.toString() + 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 != null) {
try {
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);
}
}
}
}
这样一直加载到jar文件里面去了。
如果不以classpath*开头，且路径不包含通配符的就以这个方式处理；
// a single resource with the given name
return new Resource[] {getResourceLoader().getResource(locationPattern)};
如果不以classpath开头则使用DefaultResourceLoader 处理：
public class DefaultResourceLoader implements ResourceLoader {
private ClassLoader classLoader;
/**
* Create a new DefaultResourceLoader.
* <p>ClassLoader access will happen using the thread context class loader
* at the time of this ResourceLoader's initialization.
* @see java.lang.Thread#getContextClassLoader()
*/
public DefaultResourceLoader() {
this.classLoader = ClassUtils.getDefaultClassLoader();
}
/**
* Create a new DefaultResourceLoader.
* @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(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(ClassLoader classLoader) {
this.classLoader = classLoader;
}
/**
* Return the ClassLoader to load class path resources with.
* <p>Will get passed to ClassPathResource's constructor for all
* ClassPathResource objects created by this resource loader.
* @see ClassPathResource
*/
@Override
public ClassLoader getClassLoader() {
return (this.classLoader != null ? this.classLoader : ClassUtils.getDefaultClassLoader());
}
@Override
public Resource getResource(String location) {
Assert.notNull(location, "Location must not be null");
if (location.startsWith("/")) {
return getResourceByPath(location);
}
else if (location.startsWith(CLASSPATH_URL_PREFIX)) {
return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());
}
else {
try {
// Try to parse the location as a URL...
URL url = new URL(location);
return new UrlResource(url);
}
catch (MalformedURLException ex) {
// No URL -> resolve as resource path.
return getResourceByPath(location);
}
}
最后是路径中包含通配符的，如(classpath*:resource/**/xxx.xml)
主要的思想就是
1.先获取目录，加载目录里面的所有资源
2.在所有资源里面进行查找匹配，找出我们需要的资源
/**
* 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 {
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 (rootDirResource.getURL().getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
result.addAll(VfsResourceMatchingDelegate.findMatchingResources(rootDirResource, subPattern, getPathMatcher()));
}
else if (isJarResource(rootDirResource)) {
result.addAll(doFindPathMatchingJarResources(rootDirResource, subPattern));
}
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()]);
}
我们可以总结一下：
1.无论是classpath还是classpath*都可以加载整个classpath下（包括jar包里面）的资源文件。
2.classpath只会返回第一个匹配的资源，查找路径是优先在项目中存在资源文件，再查找jar包。