Spring ClassPathResource載入資原始檔詳解
阿新 • • 發佈:2021-07-01
先看Demo
@Test public void testClassPathResource() throws IOException { Resource res = new ClassPathResource("resource/ApplicationContext.xml"); InputStream input = res.getInputStream(); Assert.assertNotNull(input); }
再看內部原始碼
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; }
獲取資源內容
/** * 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; }
原始碼解讀
該類獲取資源的方式有兩種:Class獲取和ClassLoader獲取。
@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")); }
執行結果:
/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
//獲取的是相對於當前類的相對路徑 Class.getResource("") //獲取的是classpath的根路徑 Class.getResource("/") //獲取的是classpath的根路徑 ClassLoader.getResource("")
總結
在建立ClassPathResource物件時,我們可以指定是按Class的相對路徑獲取檔案還是按ClassLoader來獲取。