五、Spring MVC 源码学习（Resource）

一、体系结构

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。

二、接口设计

         1.InputStreamSource

public interface InputStreamSource {
	InputStream getInputStream() throws IOException;
}

         2.Resource

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 relativePath) throws IOException;
	String getFilename();
	String getDescription();
}

      3.AbstractResource

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());
    }

}

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。

4.  ContextResource

public interface ContextResource extends Resource {
	String getPathWithinContext();
}

该接口具有获取上下文路径的功能

5.WritableResource

public interface WritableResource extends Resource {
	boolean isWritable();
	OutputStream getOutputStream() throws IOException;
}

添加当前的类是否可写，获取当前文件的输出流信息