spring的配置文件读取是通过 ClasspathResource进行封装的，如 new ClassPathResource("beanfactoryTest. xml),那么 ClassPathResource完成了什么功能呢？在Java中，将不同来源的资源抽象成URL,通过注册不同的 handler(URLStreamhandler)来处理不同来源的资源的读取逻辑，一般handler的类型使用不同前缀(协议，Protocol)来识別，如“fle:”、"hup:”、jar:”等，然而URL没有默认定义相对 ClassPath或 ServletContext等资源的handler,虽然可以注册自己的 URLStreamHandler来解析特定的URL前缀（协议），比如“ classpath:",然而这需要了解URL的实现机制，而且URL也没有提供一些基本的方法，如检查当前资源是否存在、检查当前资源是否可读等方法。因而 Spring对其内部使用到的资源实现了自己的抽象结构： Resource接口来封装底层资源。
public interface InputStreamSource {
/**
* Return an {@link InputStream} for the content of an underlying resource.
* <p>It is expected that each call creates a <i>fresh</i> stream.
* <p>This requirement is particularly important when you consider an API such
* as JavaMail, which needs to be able to read the stream multiple times when
* creating mail attachments. For such a use case, it is <i>required</i>
* that each {@code getInputStream()} call returns a fresh stream.
* @return the input stream for the underlying resource (must not be {@code null})
* @throws java.io.FileNotFoundException if the underlying resource doesn't exist
* @throws IOException if the content stream could not be opened
*/
InputStream getInputStream() throws IOException;
}
public interface Resource extends InputStreamSource {
/**
* Determine whether this resource actually exists in physical form.
* <p>This method performs a definitive existence check, whereas the
* existence of a {@code Resource} handle only guarantees a valid
* descriptor handle.
*/
boolean exists();
/**
* Indicate whether non-empty contents of this resource can be read via
* {@link #getInputStream()}.
* <p>Will be {@code true} for typical resource descriptors that exist
* since it strictly implies {@link #exists()} semantics as of 5.1.
* Note that actual content reading may still fail when attempted.
* However, a value of {@code false} is a definitive indication
* that the resource content cannot be read.
* @see #getInputStream()
* @see #exists()
*/
default boolean isReadable() {
return exists();
}
/**
* Indicate whether this resource represents a handle with an open stream.
* If {@code true}, the InputStream cannot be read multiple times,
* and must be read and closed to avoid resource leaks.
* <p>Will be {@code false} for typical resource descriptors.
*/
default boolean isOpen() {
return false;
}
/**
* Determine whether this resource represents a file in a file system.
* A value of {@code true} strongly suggests (but does not guarantee)
* that a {@link #getFile()} call will succeed.
* <p>This is conservatively {@code false} by default.
* @since 5.0
* @see #getFile()
*/
default boolean isFile() {
return false;
}
/**
* Return a URL handle for this resource.
* @throws IOException if the resource cannot be resolved as URL,
* i.e. if the resource is not available as descriptor
*/
URL getURL() throws IOException;
/**
* Return a URI handle for this resource.
* @throws IOException if the resource cannot be resolved as URI,
* i.e. if the resource is not available as descriptor
* @since 2.5
*/
URI getURI() throws IOException;
/**
* Return a File handle for this resource.
* @throws java.io.FileNotFoundException if the resource cannot be resolved as
* absolute file path, i.e. if the resource is not available in a file system
* @throws IOException in case of general resolution/reading failures
* @see #getInputStream()
*/
File getFile() throws IOException;
/**
* Return a {@link ReadableByteChannel}.
* <p>It is expected that each call creates a <i>fresh</i> channel.
* <p>The default implementation returns {@link Channels#newChannel(InputStream)}
* with the result of {@link #getInputStream()}.
* @return the byte channel for the underlying resource (must not be {@code null})
* @throws java.io.FileNotFoundException if the underlying resource doesn't exist
* @throws IOException if the content channel could not be opened
* @since 5.0
* @see #getInputStream()
*/
default ReadableByteChannel readableChannel() throws IOException {
return Channels.newChannel(getInputStream());
}
/**
* Determine the content length for this resource.
* @throws IOException if the resource cannot be resolved
* (in the file system or as some other known physical resource type)
*/
long contentLength() throws IOException;
/**
* Determine the last-modified timestamp for this resource.
* @throws IOException if the resource cannot be resolved
* (in the file system or as some other known physical resource type)
*/
long lastModified() throws IOException;
/**
* Create a resource relative to this resource.
* @param relativePath the relative path (relative to this resource)
* @return the resource handle for the relative resource
* @throws IOException if the relative resource cannot be determined
*/
Resource createRelative(String relativePath) throws IOException;
/**
* Determine a filename for this resource, i.e. typically the last
* part of the path: for example, "myfile.txt".
* <p>Returns {@code null} if this type of resource does not
* have a filename.
*/
@Nullable
String getFilename();
/**
* Return a description for this resource,
* to be used for error output when working with the resource.
* <p>Implementations are also encouraged to return this value
* from their {@code toString} method.
* @see Object#toString()
*/
String getDescription();
}
