Spring--ClassPathResource

/*
* 用一个给定的类加载器或者给定的类来加载资源
*/
public class ClassPathResource extends AbstractFileResolvingResource {

private final String path;

private ClassLoader classLoader;

private Class<?> clazz;

/**
* Create a new {@code ClassPathResource} for {@code ClassLoader} usage.
* A leading slash will be removed, as the ClassLoader resource access
* methods will not accept it.
* <p>The thread context class loader will be used for
* loading the resource.
* @param path the absolute path within the class path
* @see java.lang.ClassLoader#getResourceAsStream(String)
* @see org.springframework.util.ClassUtils#getDefaultClassLoader()
*/
//类路径的决定路径
public ClassPathResource(String path) {
this(path, (ClassLoader) null);
}

/**
* Create a new {@code ClassPathResource} for {@code ClassLoader} usage.
* A leading slash will be removed, as the ClassLoader resource access
* methods will not accept it.
* @param path the absolute path within the classpath
* @param classLoader the class loader to load the resource with,
* or {@code null} for the thread context class loader
* @see ClassLoader#getResourceAsStream(String)
*/
//创建一个类路径资源给类加载器使用
public ClassPathResource(String path, ClassLoader classLoader) {
Assert.notNull(path, "Path must not be null");
String pathToUse = StringUtils.cleanPath(path);
if (pathToUse.startsWith("/")) {
pathToUse = pathToUse.substring(1);
}
this.path = pathToUse;
this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());//获得默认的类加载器
}

/**
* Create a new {@code ClassPathResource} for {@code Class} usage.
* The path can be relative to the given class, or absolute within
* the classpath via a leading slash.
* @param path relative or absolute path within the class path
* @param clazz the class to load resources with
* @see java.lang.Class#getResourceAsStream
*/
public ClassPathResource(String path, Class<?> clazz) {
Assert.notNull(path, "Path must not be null");
this.path = StringUtils.cleanPath(path);
this.clazz = clazz;
}

/**
* Create a new {@code ClassPathResource} with optional {@code ClassLoader}
* and {@code Class}. Only for internal usage.
* @param path relative or absolute path within the classpath
* @param classLoader the class loader to load the resource with, if any
* @param clazz the class to load resources with, if any
*/
protected ClassPathResource(String path, ClassLoader classLoader, Class<?> clazz) {
this.path = StringUtils.cleanPath(path);
this.classLoader = classLoader;
this.clazz = clazz;
}

/**
* Return the path for this resource (as resource path within the class path).
*/
//返回资源路径
public final String getPath() {
return this.path;
}

/**
* Return the ClassLoader that this resource will be obtained from.
*/
//这个资源得到的类加载器
public final ClassLoader getClassLoader() {
return (this.clazz != null ? this.clazz.getClassLoader() : this.classLoader);
}

/**
* This implementation checks for the resolution of a resource URL.
* @see java.lang.ClassLoader#getResource(String)
* @see java.lang.Class#getResource(String)
*/
@Override
public boolean exists() {
return (resolveURL() != null);
}

/**
* Resolves a URL for the underlying class path resource.
* @return the resolved URL, or {@code null} if not resolvable
*/
//返回潜在的class 路径资源URL
protected URL resolveURL() {
if (this.clazz != null) {
return this.clazz.getResource(this.path);
}
else if (this.classLoader != null) {
return this.classLoader.getResource(this.path);
}
else {
return ClassLoader.getSystemResource(this.path);
}
}

/**
* This implementation opens an InputStream for the given class path resource.
* @see java.lang.ClassLoader#getResourceAsStream(String)
* @see java.lang.Class#getResourceAsStream(String)
*/
//
@Override
public InputStream getInputStream() throws IOException {
InputStream is;
if (this.clazz != null) {
is = this.clazz.getResourceAsStream(this.path);
}
else if (this.classLoader != null) {
is = this.classLoader.getResourceAsStream(this.path);
}
else {
is = ClassLoader.getSystemResourceAsStream(this.path);
}
if (is == null) {
throw new FileNotFoundException(getDescription() + " cannot be opened because it does not exist");
}
return is;
}

/**
* This implementation returns a URL for the underlying class path resource,
* if available.
* @see java.lang.ClassLoader#getResource(String)
* @see java.lang.Class#getResource(String)
*/
@Override
public URL getURL() throws IOException {
URL url = resolveURL();
if (url == null) {
throw new FileNotFoundException(getDescription() + " cannot be resolved to URL because it does not exist");
}
return url;
}

/**
* This implementation creates a ClassPathResource, applying the given path
* relative to the path of the underlying resource of this descriptor.
* @see org.springframework.util.StringUtils#applyRelativePath(String, String)
*/
@Override
public Resource createRelative(String relativePath) {
String pathToUse = StringUtils.applyRelativePath(this.path, relativePath);
return new ClassPathResource(pathToUse, this.classLoader, this.clazz);
}

/**
* This implementation returns the name of the file that this class path
* resource refers to.
* @see org.springframework.util.StringUtils#getFilename(String)
*/
@Override
public String getFilename() {
return StringUtils.getFilename(this.path);
}

/**
* This implementation returns a description that includes the class path location.
*/
@Override
public String getDescription() {
StringBuilder builder = new StringBuilder("class path resource [");
String pathToUse = path;
if (this.clazz != null && !pathToUse.startsWith("/")) {
builder.append(ClassUtils.classPackageAsResourcePath(this.clazz));
builder.append('/');
}
if (pathToUse.startsWith("/")) {
pathToUse = pathToUse.substring(1);
}
builder.append(pathToUse);
builder.append(']');
return builder.toString();
}

/**
* This implementation compares the underlying class path locations.
*/
@Override
public boolean equals(Object obj) {
if (obj == this) {
return true;
}
if (obj instanceof ClassPathResource) {
ClassPathResource otherRes = (ClassPathResource) obj;
return (this.path.equals(otherRes.path) &&
ObjectUtils.nullSafeEquals(this.classLoader, otherRes.classLoader) &&
ObjectUtils.nullSafeEquals(this.clazz, otherRes.clazz));
}
return false;
}

/**
* This implementation returns the hash code of the underlying
* class path location.
*/
@Override
public int hashCode() {
return this.path.hashCode();
}

}