Spring加载resource时classpath*:与classpath:的区别

Spring可以通过指定classpath*:与classpath:前缀加路径的方式从classpath加载文件,如bean的定义文件.classpath*:的出现是为了从多个jar文件中加载相同的文件.classpath:只能加载找到的第一个文件.

比如 resource1.jar中的package 'com.test.rs' 有一个 'jarAppcontext.xml' 文件,内容如下:

<bean name="ProcessorImplA" class="com.test.spring.di.ProcessorImplA" />

resource2.jar中的package 'com.test.rs' 也有一个 'jarAppcontext.xml' 文件,内容如下:

<bean id="ProcessorImplB" class="com.test.spring.di.ProcessorImplB" />

通过使用下面的代码则可以将两个jar包中的文件都加载进来

ApplicationContext ctx = new ClassPathXmlApplicationContext( "classpath*:com/test/rs/jarAppcontext.xml");

而如果写成下面的代码,就只能找到其中的一个xml文件(顺序取决于jar包的加载顺序)

ApplicationContext ctx = new ClassPathXmlApplicationContext( "classpath:com/test/rs/jarAppcontext.xml");

classpath*:的使用是为了多个component(最终发布成不同的jar包)并行开发,各自的bean定义文件按照一定的规则:package+filename,而使用这些component的调用者可以把这些文件都加载进来.

classpath*:的加载使用了classloader的

getResources()

方法,如果是在不同的J2EE服务器上运行,由于应用服务器提供自己的classloader实现，它们在处理jar文件时的行为也许会有所不同。 要测试

classpath*:

是否有效，可以用classloader从classpath中的jar文件里加载文件来进行测试：

getClass().getClassLoader().getResources("<someFileInsideTheJar>")

。(上面的例子是在sun的jre中运行的状态)

从Spring的源码,在PathMatchingResourcePatternResolver类中,我们可以更清楚的了解其对的处理:如果是以classpath*开头,它会遍历classpath.

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protected Resource[] findAllClassPathResources(String location) throws IOException {

String path = location;

if (path.startsWith("/")) {

path = path.substring(1);

}

Enumeration resourceUrls = getClassLoader().getResources(path);

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

while (resourceUrls.hasMoreElements()) {

URL 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 resourceUrls = getClassLoader().getResources(path);
Set<Resource> result = new LinkedHashSet<Resource>(16);
while (resourceUrls.hasMoreElements()) {
URL url = (URL) resourceUrls.nextElement();
result.add(convertClassLoaderURL(url));
}
return result.toArray(new Resource[result.size()]);
}

http://blog.csdn.net/kkdelta/article/details/5560210,简介了在JAVA里遍历classpath中读取找到的所有符合名称的文件.
另外在加载resource的时候,其他前缀的意义如下表所示:注意classpath*只能用与指定配置文件的路径,不能用在用于getResource的参数.如appContext.getResource("classpath*:conf/bfactoryCtx.xml")会异常的.

前缀	例子	说明
classpath:	classpath:com/myapp/config.xml	从classpath中加载。
file:	file:/data/config.xml	作为 URL 从文件系统中加载。
http:	http://myserver/logo.png	作为 URL 加载。
(none)	/data/config.xml	根据 ApplicationContext 进行判断。

从Spring的源码可以看出原因:如果是classpath:开头,从classpath加载,否则尝试URL,如果失败,调用 getResourceByPath

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public Resource getResource(String location) {

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

if (location.startsWith(CLASSPATH_URL_PREFIX)) {

returnnew ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()), getClassLoader());

}

else {

try {

// Try to parse the location as a URL...

URL url = new URL(location);

returnnew 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);
}
}
}

getResourceByPath会被不同

ApplicationContext

实现覆盖.

如 GenericWebApplicationContext覆盖为如下:

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protected Resource getResourceByPath(String path) {

returnnew ServletContextResource(this.servletContext, path);

}

如 FileSystemXmlApplicationContext覆盖为如下:

protected Resource getResourceByPath(String path) {

if (path != null && path.startsWith("/")) {

path = path.substring(1);

}

returnnew FileSystemResource(path);

}

protected Resource getResourceByPath(String path) {
return new ServletContextResource(this.servletContext, path);
}

如 FileSystemXmlApplicationContext覆盖为如下:

protected Resource getResourceByPath(String path) {
if (path != null && path.startsWith("/")) {
path = path.substring(1);
}
return new FileSystemResource(path);
}

最终从文件加载的时候仍然是JAVA中常见的读取文件的方法:

如ClassPathResource得到inputstream的方法是利用class loader.

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public InputStream getInputStream() throws IOException {

InputStream is;

if (this.clazz != null) {

is = this.clazz.getResourceAsStream(this.path);

}

public InputStream getInputStream() throws IOException {
InputStream is;
if (this.clazz != null) {
is = this.clazz.getResourceAsStream(this.path);
}

如FileSystemResource得到inputstream的方法是利用FileInputStream.

public InputStream getInputStream() throws IOException { return new FileInputStream(this.file); }

如ServletContextResource得到inputstream的方法是利用servletContext.getResourceAsStream.

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public InputStream getInputStream() throws IOException {

InputStream is = this.servletContext.getResourceAsStream(this.path);

if (is == null) {

thrownew FileNotFoundException("Could not open " + getDescription());

}

return is;

}