(造轮子)手写Spring框架-资源和资源加载器

资源和资源加载器

代码路径：github.com/WangChao-ly…

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本代码实现了spring中资源路径加载需求

1. 资源加载总共分三种方法进行加载，一种是classpath:,一种是文件系统，还有一种是URL资源定位方式，我们需要为这三个类编写一个抽象的资源接口，对外展示该接口，不涉及具体的实现。编写Resource接口如下：

/**
 * 资源的抽象和访问接口
 * @author WangChao
 * @date 2023/6/17 19:53
 */
public interface Resource {
    InputStream getInputStream() throws IOException;
}

以下三种方法都是显示了该接口，为具体的实现类：

• classpath下的资源，编写ClassPathResource如下，该类是通过类加载器获取类路径下的资源文件的输入流：

public class ClassPathResource implements Resource{
    private final String path;

    public ClassPathResource(String path){
        this.path = path;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        InputStream is = this.getClass().getClassLoader().getResourceAsStream(this.path);
        if(is == null){
            throw new FileNotFoundException(this.path + " cannot be opened because it does not exist");
        }
        return is;
    }
}

• 文件系统下的资源，先通过File类的toPath方法获取Path类实例，再通过File类的newInputStream方法获取到文件的输入流：

public class FileSystemResource implements Resource{
    private final String path;

    public FileSystemResource(String path){
        this.path = path;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        try{
            Path path = new File(this.path).toPath();
            return Files.newInputStream(path);
        }catch (NoSuchFileException ex){
            throw new FileNotFoundException(ex.toString());
        }
    }
}

• URL下的资源，该方法通过得到URLConnection类来获取文件输入流，具体代码如下：

public class UrlResource implements Resource {
    private final URL url;

    public UrlResource(URL url){
        this.url = url;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        URLConnection urlConnection = this.url.openConnection();
        try{
            return urlConnection.getInputStream();
        }catch (IOException ex) {
            throw ex;
        }
    }
}

2. 编写资源加载器接口，该接口是用来获取Resource对象，从而获取path路径对应的资源文件输入流：

public interface ResourceLoader {
    Resource getResource(String location);
}

• 编写该接口的实现类，通过解析localtion变量，决定使用哪种资源加载器来加载资源文件，代码如下：

public class DefaultResourceLoader implements ResourceLoader{
    public static final String CLASSPATH_URL_PREFIX = "classpath:";

    @Override
    public Resource getResource(String location) {
        if(location.startsWith(CLASSPATH_URL_PREFIX)){
            //classpath下的资源
            return new ClassPathResource(location.substring(CLASSPATH_URL_PREFIX.length()));
        }else{
            try {
                //尝试当成url来处理
                URL url = new URL(location);
                return new UrlResource(url);
            }catch (MalformedURLException e){
                //当成文件系统下的资源处理
                return new FileSystemResource(location);
            }
        }
    }
}

3. 总结测试：

public class ResourceAndResourceLoaderTest {
    @Test
    public void testResourceLoader() throws Exception {
        DefaultResourceLoader resourceLoader = new DefaultResourceLoader();

        //加载classpath下的资源
        Resource resource = resourceLoader.getResource("classpath:hello.txt");
        InputStream inputStream = resource.getInputStream();
        String content = IoUtil.readUtf8(inputStream);
        System.out.println(content);
        Assert.equals(content,"hello world!");

        //加载文件系统资源
        resource = resourceLoader.getResource("src/test/resources/hello.txt");
        Assert.isInstanceOf(FileSystemResource.class,resource);
        inputStream = resource.getInputStream();
        content = IoUtil.readUtf8(inputStream);
        System.out.println(content);

        //加载url资源
        resource = resourceLoader.getResource("https://www.baidu.com");
        Assert.isInstanceOf(UrlResource.class,resource);
        inputStream = resource.getInputStream();
        content = IoUtil.readUtf8(inputStream);
        System.out.println(content);
    }
}