每日一则JavaWeb---Spring的ResourceLoader的作用

先来看看的源码

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();

}

非常简单就两个功能，一个是获取Resource，一个是获取ClassLoader

看看默认实现又有啥，在Spring的默认套路中除了一些标志性的接口如aware接口，一般abstract和interface都会有一个DefaultXXX的默认实现。

DefaultResourceLoader怎么实现的

public class DefaultResourceLoader implements ResourceLoader {

	private ClassLoader classLoader;

	public DefaultResourceLoader() {
		this.classLoader = ClassUtils.getDefaultClassLoader();
	}

	public DefaultResourceLoader(ClassLoader classLoader) {
		this.classLoader = classLoader;
	}

	public void setClassLoader(ClassLoader classLoader) {
		this.classLoader = classLoader;
	}

	@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);
			}
		}
	}

	protected Resource getResourceByPath(String path) {
		return new ClassPathContextResource(path, getClassLoader());
	}


	protected static class ClassPathContextResource extends ClassPathResource implements ContextResource {

		public ClassPathContextResource(String path, 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());
		}
	}

}

看着实现其实没有太多可以讲的，可以看看ClassLoader的加载的过程

public static ClassLoader getDefaultClassLoader() {
		ClassLoader cl = null;
		try {
			cl = Thread.currentThread().getContextClassLoader();
		}
		catch (Throwable ex) {
			// Cannot access thread context ClassLoader - falling back...
		}
		if (cl == null) {
			// No thread context class loader -> use class loader of this class.
			cl = ClassUtils.class.getClassLoader();
			if (cl == null) {
				// getClassLoader() returning null indicates the bootstrap ClassLoader
				try {
					cl = ClassLoader.getSystemClassLoader();
				}
				catch (Throwable ex) {
					// Cannot access system ClassLoader - oh well, maybe the caller can live with null...
				}
			}
		}
		return cl;
	}

ResourcePatternResolver

其中这个接口对ResourceLoader进行了扩展，但是扩展也就是扩展 了通过多个文件的情形。。。

String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;

String CLASSPATH_ALL_URL_PREFIX = "classpath*:";

public interface ResourcePatternResolver extends ResourceLoader {

	String CLASSPATH_ALL_URL_PREFIX = "classpath*:";

	Resource[] getResources(String locationPattern) throws IOException;

}