推荐订阅源

先看Demo

@Test
public void testClassPathResource() throws IOException {
    Resource res = new ClassPathResource("resource/ApplicationContext.xml");
    InputStream input = res.getInputStream();
    Assert.assertNotNull(input);
}

再看内部源码

public ClassPathResource(String path) {
     this(path, (ClassLoader) null);
}

public ClassPathResource(String path, ClassLoader classLoader) {
    Assert.notNull(path, "Path must not be null");
    String pathToUse = StringUtils.cleanPath(path);
    if (pathToUse.startsWith("/")) {
        pathToUse = pathToUse.substring(1);
    }
    this.path = pathToUse;
    this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
}

public ClassPathResource(String path, Class<?> clazz) {
     Assert.notNull(path, "Path must not be null");
     this.path = StringUtils.cleanPath(path);
     this.clazz = clazz;
}

获取资源内容

/**
 * This implementation opens an InputStream for the given class path resource.
 * @see java.lang.ClassLoader#getResourceAsStream(String)
 * @see java.lang.Class#getResourceAsStream(String)
 */
@Override
public InputStream getInputStream() throws IOException {
    InputStream is;
    if (this.clazz != null) {
        is = this.clazz.getResourceAsStream(this.path);
    }
    else if (this.classLoader != null) {
        is = this.classLoader.getResourceAsStream(this.path);
    }
    else {
        is = ClassLoader.getSystemResourceAsStream(this.path);
    }
    if (is == null) {
        throw new FileNotFoundException(getDescription() + " cannot be opened because it does not exist");
    }
    return is;
}

源码解读

该类获取资源的方式有两种：Class获取和ClassLoader获取。

@Test
public void testResouce() {
    ClassLoader loader = Thread.currentThread().getContextClassLoader();
    System.out.println(loader.getResource("").getPath());
    System.out.println(this.getClass().getResource("").getPath());
    System.out.println(this.getClass().getResource("/").getPath());
    System.out.println(System.getProperty("user.dir"));
}

运行结果：

/home/temp/spring_test/target/test-classes/
/home/temp/spring_test/target/test-classes/com/test/spring/spring_test/
/home/temp/spring_test/target/test-classes/
/home/temp/spring_test

//获取的是相对于当前类的相对路径
Class.getResource("")
//获取的是classpath的根路径
Class.getResource("／")
//获取的是classpath的根路径
ClassLoader.getResource("")

总结

在创建ClassPathResource对象时，我们可以指定是按Class的相对路径获取文件还是按ClassLoader来获取。