关于Spring加载classpath与classpath*的过程剖析

本篇文章是由朋友的一篇博客引出的，博客原文地址：/content/2589392.html
他这篇博客比较细的讲解了classpath与classpath*，以及通配符的使用，那些配置能成功加载到资源，那些配置加载不了资源。但是我相信仍然有很多同学不明白，为什么是这样的，知其然，不知其所以然，那么本篇文章将慢慢为你揭开神秘的面纱，让你知其然，更知其所以然。

关于Spring Resource的资源类型以及继承体系我们已经在上一篇文件粗略的说了一下。Spring加载Resource文件是通过ResourceLoader来进行的，那么我们就先来看看ResourceLoader的继承体系，让我们对这个模块有一个比较系统的认知。



上图仅右边的继承体系，仅画至AbstractApplicationContext，由于ApplicationContext的继承体系，我们已经在前面章节给出，所以为了避免不必要的复杂性，本章继承体系就不引入ApplicationContext。

我们还是来关注本章的重点————classpath 与 classpath*以及通配符是怎么处理的

首先，我们来看下ResourceLoader的源码

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public interface ResourceLoader {

/** Pseudo URL prefix for loading from the class path: "classpath:" */

String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;

Resource getResource(String location);

ClassLoader getClassLoader();

}

public interface ResourceLoader {

/** Pseudo URL prefix for loading from the class path: "classpath:" */
String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;

Resource getResource(String location);

ClassLoader getClassLoader();

}

我们发现，其实ResourceLoader接口只提供了classpath前缀的支持。而classpath*的前缀支持是在它的子接口ResourcePatternResolver中。

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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*:";

Resource[] getResources(String locationPattern)
throws IOException;

}

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*:";

Resource[] getResources(String locationPattern) throws IOException;

}

通过2个接口的源码对比，我们发现ResourceLoader提供 classpath下单资源文件的载入，而ResourcePatternResolver提供了多资源文件的载入。

ResourcePatternResolver有一个实现类：PathMatchingResourcePatternResolver，那我们直奔主题，查看PathMatchingResourcePatternResolver的getResources()

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public Resource[] getResources(String locationPattern)
throws IOException {
Assert.notNull(locationPattern, "Location pattern must not be null");

//是否以classpath*开头

if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {

//是否包含?或者*

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;
//是否包含?或者*

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)};

}
}
}

public Resource[] getResources(String locationPattern) throws IOException {
Assert.notNull(locationPattern, "Location pattern must not be null");
//是否以classpath*开头
if (locationPattern.startsWith(CLASSPATH_ALL_URL_PREFIX)) {
//是否包含?或者*
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;
//是否包含?或者*
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)};
}
}
}

由此我们可以看出在加载配置文件时，以是否是以classpath*开头分为2大类处理场景，每大类在又根据路径中是否包括通配符分为2小类进行处理，

处理的流程图如下：



从上图看，整个加载资源的场景有三条处理流程

以classpath*开头，但路径不包含通配符的

让我们来看看findAllClassPathResources是怎么处理的

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protected Resource[] findAllClassPathResources(String location)
throws IOException {
String path = location;
if (path.startsWith("/")) {

path = path.substring(1);

}
Enumeration<URL> resourceUrls = getClassLoader().getResources(path);

Set<Resource> result = new LinkedHashSet<Resource>(16);

while (resourceUrls.hasMoreElements()) {

URL url = resourceUrls.nextElement();
result.add(convertClassLoaderURL(url));
}
return result.toArray(new Resource[result.size()]);

}

protected Resource[] findAllClassPathResources(String location) throws IOException {
String path = location;
if (path.startsWith("/")) {
path = path.substring(1);
}
Enumeration<URL> resourceUrls = getClassLoader().getResources(path);
Set<Resource> result = new LinkedHashSet<Resource>(16);
while (resourceUrls.hasMoreElements()) {
URL url = resourceUrls.nextElement();
result.add(convertClassLoaderURL(url));
}
return result.toArray(new Resource[result.size()]);
}

我们可以看到，最关键的一句代码是：Enumeration<URL> resourceUrls = getClassLoader().getResources(path);

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public ClassLoader getClassLoader() {

return getResourceLoader().getClassLoader();

}

public ResourceLoader getResourceLoader() {

return this.resourceLoader;

}

//默认情况下
public PathMatchingResourcePatternResolver() {

this.resourceLoader =
new DefaultResourceLoader();
}

public ClassLoader getClassLoader() {
return getResourceLoader().getClassLoader();
}

public ResourceLoader getResourceLoader() {
return this.resourceLoader;
}

//默认情况下
public PathMatchingResourcePatternResolver() {
this.resourceLoader = new DefaultResourceLoader();
}

其实上面这3个方法不是最关键的，之所以贴出来，是让大家清楚整个调用链，其实这种情况最关键的代码在于ClassLoader的getResources()方法。那么我们同样跟进去，看看源码

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public Enumeration<URL> getResources(String name)
throws IOException {
Enumeration[] tmp = new Enumeration[2];

if (parent != null) {

tmp[0] = parent.getResources(name);

} else {
tmp[0] = getBootstrapResources(name);

}
tmp[1] = findResources(name);

return new CompoundEnumeration(tmp);

}

public Enumeration<URL> getResources(String name) throws IOException {
Enumeration[] tmp = new Enumeration[2];
if (parent != null) {
tmp[0] = parent.getResources(name);
} else {
tmp[0] = getBootstrapResources(name);
}
tmp[1] = findResources(name);

return new CompoundEnumeration(tmp);
}

是不是一目了然了？当前类加载器，如果存在父加载器，则向上迭代获取资源， 因此能加到jar包里面的资源文件。

不以classpath*开头，且路径不包含通配符的

处理逻辑如下

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return new Resource[] {getResourceLoader().getResource(locationPattern)};

return new Resource[] {getResourceLoader().getResource(locationPattern)};

上面我们已经贴过getResourceLoader()的逻辑了， 即默认是DefaultResourceLoader()，那我们进去看看getResouce()的实现

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public Resource getResource(String location) {

Assert.notNull(location, "Location must not be null");

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);

}
}
}

public Resource getResource(String location) {
Assert.notNull(location, "Location must not be null");
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);
}
}
}

其实很简单，如果以classpath开头，则创建为一个ClassPathResource，否则则试图以URL的方式加载资源，创建一个UrlResource.

路径包含通配符的

这种情况是最复杂的，涉及到层层递归，那我把加了注释的代码发出来大家看一下，其实主要的思想就是
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

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protected Resource[] findPathMatchingResources(String locationPattern)
throws IOException {
//拿到能确定的目录，即拿到不包括通配符的能确定的路径 比如classpath*:/aaa/bbb/spring-*.xml 则返回classpath*:/aaa/bbb/ //如果是classpath*:/aaa/*/spring-*.xml，则返回 classpath*:/aaa/

String rootDirPath = determineRootDir(locationPattern);

//得到spring-*.xml
String subPattern = locationPattern.substring(rootDirPath.length());

//递归加载所有的根目录资源，要注意的是递归的时候又得考虑classpath,与classpath*的情况，而且还得考虑根路径中是否又包含通配符，参考上面那张流程图

Resource[] rootDirResources = getResources(rootDirPath);

Set<Resource> result = new LinkedHashSet<Resource>(16);

//将根目录所有资源中所有匹配我们需要的资源(如spring-*)加载result中

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()]);

}

protected Resource[] findPathMatchingResources(String locationPattern) throws IOException {
//拿到能确定的目录，即拿到不包括通配符的能确定的路径  比如classpath*:/aaa/bbb/spring-*.xml 则返回classpath*:/aaa/bbb/                                     //如果是classpath*:/aaa/*/spring-*.xml，则返回 classpath*:/aaa/
String rootDirPath = determineRootDir(locationPattern);
//得到spring-*.xml
String subPattern = locationPattern.substring(rootDirPath.length());
//递归加载所有的根目录资源，要注意的是递归的时候又得考虑classpath,与classpath*的情况，而且还得考虑根路径中是否又包含通配符，参考上面那张流程图
Resource[] rootDirResources = getResources(rootDirPath);
Set<Resource> result = new LinkedHashSet<Resource>(16);
//将根目录所有资源中所有匹配我们需要的资源(如spring-*)加载result中
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()]);
}

值得注解一下的是determineRootDir()方法的作用，是确定根目录，这个根目录必须是一个能确定的路径，不会包含通配符。如果classpath*:aa/bb*/spring-*.xml，得到的将是classpath*:aa/ 可以看下他的源码

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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);

}

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);
}

分析到这，结合测试我们可以总结一下：
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。
3.文件名字包含通配符资源(如果spring-*.xml，spring*.xml)， 如果根目录为""， classpath加载不到任何资源， 而classpath*则可以加载到classpath中可以匹配的目录中的资源，但是不能加载到jar包中的资源

第1，2点比较好表理解，大家可以自行测试，第三点表述有点绕，举个例，现在有资源文件结构如下：



classpath:notice*.txt 加载不到资源

classpath*:notice*.txt 加载到resource根目录下notice.txt
classpath:META-INF/notice*.txt 加载到META-INF下的一个资源（classpath是加载到匹配的第一个资源，就算删除classpath下的notice.txt，他仍然可以 加载jar包中的notice.txt）

classpath:META-*/notice*.txt 加载不到任何资源

classpath*:META-INF/notice*.txt 加载到classpath以及所有jar包中META-INF目录下以notice开头的txt文件

classpath*:META-*/notice*.txt 只能加载到classpath下 META-INF目录的notice.txt

大家感觉一下吧