Spring源码分析——资源访问利器Resource之实现类分析

　　今天来分析Spring的资源接口Resource的各个实现类。关于它的接口和抽象类，参见上一篇博文——Spring源码分析——资源访问利器Resource之接口和抽象类分析

　　一、文件系统资源 FileSystemResource

　　文件系统资源 FileSystemResource，资源以文件系统路径的方式表示。这个类继承自AbstractResource，并实现了写的接口WritableResource。类全称为public class FileSystemResource extends AbstractResource implements WritableResource 。这个资源类是所有Resource实现类中，唯一一个实现了WritableResource接口的类。就是说，其他的类都不可写入操作，都只能读取。部分翻译注释后，源码如下：（以后不重要的源码我就折叠起来）　

/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.core.io;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URI;
import java.net.URL;

import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

/**
 * @author Juergen Hoeller
 * @since 28.12.2003
 * @see java.io.File
 */
public class FileSystemResource extends AbstractResource implements WritableResource {

    private final File file;   //  不可变属性

    private final String path; //  不可变属性

    public FileSystemResource(File file) { //  简单的构造方法，path为file路径格式化后的样子
        Assert.notNull(file, "File must not be null");
        this.file = file;
        this.path = StringUtils.cleanPath(file.getPath());
    }

    public FileSystemResource(String path) {   //简单的构造方法
        Assert.notNull(path, "Path must not be null");
        this.file = new File(path);
        this.path = StringUtils.cleanPath(path);
    }

    public final String getPath() {    //新增的方法，返回资源路径，方法不可重写
        return this.path;
    }

    @Override
    public boolean exists() {  
        return this.file.exists();
    }

    @Override
    public boolean isReadable() {
        return (this.file.canRead() && !this.file.isDirectory());
    }

    public InputStream getInputStream() throws IOException {   //InputStreamSource接口的实现方法
        return new FileInputStream(this.file);
    }

    @Override
    public URL getURL() throws IOException {   //可见这个url是通过uri得到的
        return this.file.toURI().toURL();
    }

    @Override
    public URI getURI() throws IOException {
        return this.file.toURI();
    }

    @Override
    public File getFile() {
        return this.file;
    }

    @Override
    public long contentLength() throws IOException {   
        return this.file.length();
    }

    @Override
    public Resource createRelative(String relativePath) {
        String pathToUse = StringUtils.applyRelativePath(this.path, relativePath);
        return new FileSystemResource(pathToUse);
    }

    @Override
    public String getFilename() {
        return this.file.getName();
    }
    
    public String getDescription() {   //  资源描述，直接用绝对路径来构造
        return "file [" + this.file.getAbsolutePath() + "]";
    }

    public boolean isWritable() {  //  WritableResource接口的实现方法
        return (this.file.canWrite() && !this.file.isDirectory());
    }

    public OutputStream getOutputStream() throws IOException {
        return new FileOutputStream(this.file);
    }

    @Override
    public boolean equals(Object obj) {    //通过path来比较
        return (obj == this ||
            (obj instanceof FileSystemResource && this.path.equals(((FileSystemResource) obj).path)));
    }

    @Override
    public int hashCode() {    //  文件资源的HashCode就是path的hashCode
        return this.path.hashCode();
    }

}

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