样例
/**
* 测试通过三种方式加载文件
*
* @author chaozai
* @date 2019年9月23日
*
*/
public class ResourceLoaderTest {
private static final String TEST_FILE_PATH_FOR_CLASS_1 = "test.txt";
private static final String TEST_FILE_PATH_FOR_CLASS_2 = "/resource/test.txt";
private static final String TEST_FILE_PATH_FOR_CLASSLOADER = "resource/test.txt";
public static void main(String[] args) {
//class.getResource:不以/开头，相对于当前class文件所在路径查找
System.out.println(ResourceLoaderTest.class.getResource(TEST_FILE_PATH_FOR_CLASS_1));
//class.getResource:以/开头，则相对于跟路径查找
System.out.println(ResourceLoaderTest.class.getResource(TEST_FILE_PATH_FOR_CLASS_2));
//classLoader.getResource:不以/开头，相对于跟路径查找
System.out.println(ResourceLoaderTest.class.getClassLoader().getResource(TEST_FILE_PATH_FOR_CLASSLOADER));
//ClassLoader.getSystemClassLoader().getResource:同classLoader
System.out.println(ClassLoader.getSystemClassLoader().getResource(TEST_FILE_PATH_FOR_CLASSLOADER));
//错误样例
System.out.println(ResourceLoaderTest.class.getResource(TEST_FILE_PATH_FOR_CLASSLOADER));
System.out.println(ResourceLoaderTest.class.getClassLoader().getResource(TEST_FILE_PATH_FOR_CLASS_2));
System.out.println(ClassLoader.getSystemClassLoader().getResource(TEST_FILE_PATH_FOR_CLASS_2));
}
}结果：
file:/D:/workspace/java/studyworkspace/JavaTest/bin/resource/test.txt
file:/D:/workspace/java/studyworkspace/JavaTest/bin/resource/test.txt
file:/D:/workspace/java/studyworkspace/JavaTest/bin/resource/test.txt
file:/D:/workspace/java/studyworkspace/JavaTest/bin/resource/test.txt
null
null
null结论：
- class的getResource不以/开头，会从class这个类所在的目录开始搜索资源，如果以/开头,会从工程的根目录开始搜索
- classloader的getResource不以/开头，会从工程的根目录开始搜索资源
- classLoader的getSystemResource方法与classloader的getResource相同，当无法获取线程上下文，且类的父加载器是Bootstrap加载器时，可以选择这种方式
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