spring resource

Spring资源抽象Resource,JDK操纵底层资源基本就是 java.net.URL 、java.io.File 、java.util.Properties,取资源基本是根据绝对路径或当前类的相对路径来取。从类路径或Web容器上下文中获取资源的时候也不方便。Resource接口提供了更强大的访问底层资源的能力。

Resouce 接口

直接继承了JDK的InputStream，看源码

package org.springframework.core.io;

import java.io.File;
import java.io.IOException;
import java.net.URI;
import java.net.URL;
import org.springframework.core.io.InputStreamSource;

public interface Resource extends InputStreamSource {
    boolean exists();

    boolean isReadable();

    boolean isOpen();

    URL getURL() throws IOException;

    URI getURI() throws IOException;

    File getFile() throws IOException;

    long contentLength() throws IOException;

    long lastModified() throws IOException;

    Resource createRelative(String var1) throws IOException; //相对的路径下创建一个文件

    String getFilename();

    String getDescription();
}

抽象类AbstractResource

Convenience base class for {@link Resource} implementations,pre-implementing typical behavior.对于任何的接口而言，这个直接抽象类是重中之重，里面浓缩了接口的大部分公共实现,其中大量的使用了模板方法模式,留给子类去实现这些具体的资源对应的处理的方式。

public abstract class AbstractResource implements Resource {
    public AbstractResource() {
    }

    public boolean exists() {
        try {
            return this.getFile().exists(); //子类获取getFile
        } catch (IOException var4) {
            try {
                InputStream isEx = this.getInputStream(); //获取流，还是没有不存在哦
                isEx.close();//可能有的资源只有流信息，没有文件信息，比如http路径
                return true;
            } catch (Throwable var3) {
                return false;
            }
        }
    }

    public boolean isReadable() {
        return true;
    }

    public boolean isOpen() {
        return false;
    }

    public URL getURL() throws IOException { //留给子类去特定的实现
        throw new FileNotFoundException(this.getDescription() + " cannot be resolved to URL");
    }

    public URI getURI() throws IOException {
        URL url = this.getURL();

        try {
            return ResourceUtils.toURI(url);
        } catch (URISyntaxException var3) {
            throw new NestedIOException("Invalid URI [" + url + "]", var3);
        }
    }

    public File getFile() throws IOException {//留给子类去实现
        throw new FileNotFoundException(this.getDescription() + " cannot be resolved to absolute file path");
    }

    public long contentLength() throws IOException { //计算长度哦
        InputStream is = this.getInputStream();
        Assert.state(is != null, "resource input stream must not be null");

        try {
            long size = 0L;

            int read;
            for(byte[] buf = new byte[255]; (read = is.read(buf)) != -1; size += (long)read) {
                ;
            }

            long var6 = size;
            return var6;
        } finally {
            try {
                is.close();
            } catch (IOException var14) {
                ;
            }

        }
    }

    public long lastModified() throws IOException {
        long lastModified = this.getFileForLastModifiedCheck().lastModified();
        if(lastModified == 0L) {
            throw new FileNotFoundException(this.getDescription() + " cannot be resolved in the file system for resolving its last-modified timestamp");
        } else {
            return lastModified;
        }
    }

    protected File getFileForLastModifiedCheck() throws IOException {
        return this.getFile();
    }

    public Resource createRelative(String relativePath) throws IOException { //创建相对路径下的文件夹的信息，由子类去实现
        throw new FileNotFoundException("Cannot create a relative resource for " + this.getDescription());
    }

    public String toString() {
        return this.getDescription();
    }

    public boolean equals(Object obj) {
        return obj == this || obj instanceof Resource && ((Resource)obj).getDescription().equals(this.getDescription());
    }

}

Resource的子接口的信息ContextResource and WritableResource

WritableResource:添加当前的类是否可写，获取当前文件的输出流信息
ContextResource:获取上下文路径
1 ContextResource添加了一个接口

  public interface ContextResource extends Resource {

    /**
     * Return the path within the enclosing 'context'.
     * <p >This is typically path relative to a context-specific root directory,
     * e.g. a ServletContext root or a PortletContext root.
     */
    String getPathWithinContext(); //获取上下文的路径的信息

  }  

2 WritableResource判断当前文件的可写

public interface WritableResource extends Resource {
    boolean isWritable();

    OutputStream getOutputStream() throws IOException;//获取输出流的信息
}

重要的抽象类AbstractFileResolvingResource

这个抽象类继承自AbstractResource，重写了AbstractResource的大部分方法。resolve URLs into File references!将URL类型的文件进行转换。

/**
 * Abstract base class for resources which resolve URLs into File references,
 * such as {@link UrlResource} or {@link ClassPathResource}.
 *
 * <p>Detects the "file" protocol as well as the JBoss "vfs" protocol in URLs,
 * resolving file system references accordingly.
 *
 * @author Juergen Hoeller
 * @since 3.0
 */
public abstract class AbstractFileResolvingResource extends AbstractResource {

    /**
     * This implementation returns a File reference for the underlying class path
     * resource, provided that it refers to a file in the file system.
     * @see org.springframework.util.ResourceUtils#getFile(java.net.URL, String)
     */
    @Override
    public File getFile() throws IOException { //  通过资源的URL得到资源本身
        URL url = getURL();
        if (url.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
            return VfsResourceDelegate.getResource(url).getFile();
        }
        return ResourceUtils.getFile(url, getDescription());
    }

    /**
     * This implementation determines the underlying File
     * (or jar file, in case of a resource in a jar/zip).
     */
    @Override
    protected File getFileForLastModifiedCheck() throws IOException { //内部使用
        URL url = getURL();
        if (ResourceUtils.isJarURL(url)) {
            URL actualUrl = ResourceUtils.extractJarFileURL(url);
            if (actualUrl.getProtocol().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
                return VfsResourceDelegate.getResource(actualUrl).getFile();
            }
            return ResourceUtils.getFile(actualUrl, "Jar URL");
        }
        else {
            return getFile();
        }
    }

    /**
     * This implementation returns a File reference for the underlying class path
     * resource, provided that it refers to a file in the file system.
     * @see org.springframework.util.ResourceUtils#getFile(java.net.URI, String)
     */
    protected File getFile(URI uri) throws IOException { //  通过资源uri获取文件
        if (uri.getScheme().startsWith(ResourceUtils.URL_PROTOCOL_VFS)) {
            return VfsResourceDelegate.getResource(uri).getFile();
        }
        return ResourceUtils.getFile(uri, getDescription());
    }


    @Override
    public boolean exists() { //判断资源是否存在，如果是文件Url,直接获取文件判断，否则，建立连接来判断。
        try {
            URL url = getURL();
            if (ResourceUtils.isFileURL(url)) {
                // Proceed with file system resolution...
                return getFile().exists();
            }
            else {
                // Try a URL connection content-length header...
                URLConnection con = url.openConnection();
                customizeConnection(con);
                HttpURLConnection httpCon =
                        (con instanceof HttpURLConnection ? (HttpURLConnection) con : null);
                if (httpCon != null) {
                    int code = httpCon.getResponseCode();
                    if (code == HttpURLConnection.HTTP_OK) {
                        return true;
                    }
                    else if (code == HttpURLConnection.HTTP_NOT_FOUND) {
                        return false;
                    }
                }
                if (con.getContentLength() >= 0) {
                    return true;
                }
                if (httpCon != null) {
                    // no HTTP OK status, and no content-length header: give up
                    httpCon.disconnect();
                    return false;
                }
                else {
                    // Fall back to stream existence: can we open the stream?
                    InputStream is = getInputStream();
                    is.close();
                    return true;
                }
            }
        }
        catch (IOException ex) {
            return false;
        }
    }

    @Override
    public boolean isReadable() { //  是否可读
        try {
            URL url = getURL();
            if (ResourceUtils.isFileURL(url)) {
                // Proceed with file system resolution...
                File file = getFile();
                return (file.canRead() && !file.isDirectory());
            }
            else {
                return true;
            }
        }
        catch (IOException ex) {
            return false;
        }
    }

    @Override
    public long contentLength() throws IOException {
        URL url = getURL();
        if (ResourceUtils.isFileURL(url)) {
            // Proceed with file system resolution...
            return getFile().length();
        }
        else {
            // Try a URL connection content-length header...
            URLConnection con = url.openConnection();
            customizeConnection(con);
            return con.getContentLength();
        }
    }

    @Override
    public long lastModified() throws IOException {
        URL url = getURL();
        if (ResourceUtils.isFileURL(url) || ResourceUtils.isJarURL(url)) {
            // Proceed with file system resolution...
            return super.lastModified();
        }
        else {
            // Try a URL connection last-modified header...
            URLConnection con = url.openConnection();
            customizeConnection(con);
            return con.getLastModified();
        }
    }


    /**
     * Inner delegate class, avoiding a hard JBoss VFS API dependency at runtime.
     */
    private static class VfsResourceDelegate {

        public static Resource getResource(URL url) throws IOException {
            return new VfsResource(VfsUtils.getRoot(url));
        }

        public static Resource getResource(URI uri) throws IOException {
            return new VfsResource(VfsUtils.getRoot(uri));
        }
    }

}

jar URL地址解读
URL URI 的区别
[scheme:]scheme-specific-part[#fragment]