Spring 资源文件处理
时间:2022-07-24
本文章向大家介绍Spring 资源文件处理,主要内容包括其使用实例、应用技巧、基本知识点总结和需要注意事项,具有一定的参考价值,需要的朋友可以参考一下。
Java中,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的类型使用不同的前缀(协议,protocal)来识别,如:“file:”、“http:“、”jar:”等。
对于Spring,URL没有定义相应的,如“classpath:“的handler,定义也相对麻烦,Spring对配置文件的读取做了相应的封装,通过Resource接口来抽象底层资源。如下:
/**
* Interface for a resource descriptor that abstracts from the actual
* type of underlying resource, such as a file or class path resource.
*
* <p>An InputStream can be opened for every resource if it exists in
* physical form, but a URL or File handle can just be returned for
* certain resources. The actual behavior is implementation-specific.
*
* @author Juergen Hoeller
* @since 28.12.2003
* @see #getInputStream()
* @see #getURL()
* @see #getURI()
* @see #getFile()
* @see WritableResource
* @see ContextResource
* @see FileSystemResource
* @see ClassPathResource
* @see UrlResource
* @see ByteArrayResource
* @see InputStreamResource
* @see PathResource
*/
public interface Resource extends InputStreamSource {
/**
* Return 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();
/**
* Return whether the contents of this resource can be read,
* e.g. via {@link #getInputStream()} or {@link #getFile()}.
* <p>Will be {@code true} for typical resource descriptors;
* 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()
*/
boolean isReadable();
/**
* Return whether this resource represents a handle with an open
* stream. If 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.
*/
boolean isOpen();
/**
* 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
*/
URI getURI() throws IOException;
/**
* Return a File handle for this resource.
* @throws IOException if the resource cannot be resolved as absolute
* file path, i.e. if the resource is not available in a file system
*/
File getFile() throws IOException;
/**
* 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.
*/
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();
}
对于不同来源的资源文件都有相应的Resource实现:
1. 文件(FileSystemResource)
2. Classpath资源(ClassPathResource)
3. URL资源(UrlResource)
4. InputStream资源(InputStreamResource)
5. Byte数组资源(ByteArrayResource)等。
ClassPathResource实现:
this.class.getResourceAsStream(this.path);
FileSystemResource实现:
new FileInputStream(this.file);
... ...
Resource实现返回InputStream,后续由XmlBeanDefinitionReader进行操作,如下:
配置文件加载流程
ResourceLoader:资源加载器,根据资源地址返回Resource。EncodedResource封装(处理编码)
↓↓
↓↓委托
↓↓
DocumentLoader(DefaultDocumentLoader):转换Resource为Document。SAX读取XML文件获取InputStream构造解析InputSource返回Documet。
↓↓
↓↓
↓↓
BeanDefinitionDocumentReader(DefaultBeanDefinitionDocumentReader)(单一职责应用):解析Document,注册bean。registerBeanDefinitions(doRegisterBeanDefinitions)
DefaultBeanDefinitionDocumentReader:包含preXmlProcess和postXmlProcess两个空的模板方法,供子类做相应处理。
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