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

Spring能够经过指定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.

好比 resource1.jar中的package 'com.test.rs' 有一个 'jarAppcontext.xml' 文件,内容以下:

<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,内容以下:

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

经过使用下面的代码则能够将两个jar包中的文件都加载进来

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

而若是写成下面的代码,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(最终发布成不一样的jar包)并行开发,各自的bean定义文件按照必定的规则:package+filename,而使用这些component的调用者能够把这些文件都加载进来.

classpath*:的加载使用了classloader的 getResources() 方法,若是是在不一样的J2EE服务器上运行,因为应用服务器提供本身的classloader实现，它们在处理jar文件时的行为也许会有所不一样。 要测试classpath*: 是否有效，能够用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,咱们能够更清楚的了解其对的处理:若是是以classpath*开头,它会遍历classpath.

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中读取找到的全部符合名称的文件.

 

另外在加载resource的时候,其余前缀的意义以下表所示: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	做为 URL 从文件系统中加载。
http:	http://myserver/logo.png	做为 URL 加载。
(none)	/data/config.xml	根据 ApplicationContext 进行判断。

从Spring的源码能够看出缘由:若是是classpath:开头,从classpath加载,不然尝试URL,若是失败,调用 getResourceByPath

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会被不一样ApplicationContext 实现覆盖.

如 GenericWebApplicationContext覆盖为以下:

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

如 FileSystemXmlApplicationContext覆盖为以下:

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覆盖为以下:

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获得inputstream的方法是利用class loader.

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获得inputstream的方法是利用FileInputStream.

 

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

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

public InputStream getInputStream() throws IOException {
    InputStream is = this.servletContext.getResourceAsStream(this.path);
    if (is == null) {
        thrownew FileNotFoundException("Could not open " + getDescription());
    }
    return is;
}