Spring之ClassPathResource加载资源文件

先看Demo:

1 @Test
2 public void testClassPathResource() throws IOException {
3     Resource res = new ClassPathResource("resource/ApplicationContext.xml");
4     InputStream input = res.getInputStream();
5     Assert.assertNotNull(input);
6 }

再看内部源码：

1 public ClassPathResource(String path) {
2     this(path, (ClassLoader) null);
3 }

1 public ClassPathResource(String path, ClassLoader classLoader) {
2     Assert.notNull(path, "Path must not be null");
3     String pathToUse = StringUtils.cleanPath(path);
4     if (pathToUse.startsWith("/")) {
5         pathToUse = pathToUse.substring(1);
6     }
7     this.path = pathToUse;
8     this.classLoader = (classLoader != null ? classLoader : ClassUtils.getDefaultClassLoader());
9 }

1 public ClassPathResource(String path, Class<?> clazz) {
2     Assert.notNull(path, "Path must not be null");
3     this.path = StringUtils.cleanPath(path);
4     this.clazz = clazz;
5 }

获取资源内容：

 1 /**
 2  * This implementation opens an InputStream for the given class path resource.
 3  * @see java.lang.ClassLoader#getResourceAsStream(String)
 4  * @see java.lang.Class#getResourceAsStream(String)
 5  */
 6 @Override
 7 public InputStream getInputStream() throws IOException {
 8     InputStream is;
 9     if (this.clazz != null) {
10         is = this.clazz.getResourceAsStream(this.path);
11     }
12     else if (this.classLoader != null) {
13         is = this.classLoader.getResourceAsStream(this.path);
14     }
15     else {
16         is = ClassLoader.getSystemResourceAsStream(this.path);
17     }
18     if (is == null) {
19         throw new FileNotFoundException(getDescription() + " cannot be opened because it does not exist");
20     }
21     return is;
22 }

源码解读：

该类获取资源的方式有两种：Class获取和ClassLoader获取。

两种方法的区别：

再看Demo:

 1 @Test
 2 public void testResouce() {
 3     ClassLoader loader = Thread.currentThread().getContextClassLoader();
 4     System.out.println(loader.getResource("").getPath());
 5
 6     System.out.println(this.getClass().getResource("").getPath());
 7     System.out.println(this.getClass().getResource("/").getPath());
 8
 9     System.out.println(System.getProperty("user.dir"));
10 }

运行结果：

1 2 3 4

/home/sunny/workspace/spring-01/target/test-classes/ /home/sunny/workspace/spring-01/target/test-classes/com/me/spring/spring_01/ /home/sunny/workspace/spring-01/target/test-classes/ /home/sunny/workspace/spring-01

Class.getResource("")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

ClassLoader.getResource("")获取的是classpath的根路径

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。