mov load color () tar type 當前 blog ase

本文主要是研究下面集中方法到底誰才能真正的load到文件,你能一眼看出來嗎？

GetResourcesSample.class.getClassLoader.getResourceAsStream("main-resources-file.txt") GetResourcesSample.class.getClass().getResourceAsStream("main-resources-file.txt") GetResourcesSample.class.getResourceAsStream("main-resources-file.txt") GetResourcesSample.class.getClassLoader.getResourceAsStream("/main-resources-file.txt") GetResourcesSample.class.getClass().getResourceAsStream("/main-resources-file.txt") GetResourcesSample.class.getResourceAsStream("/main-resources-file.txt") 很暈吧，反正我是挺暈的。

目錄結構：

代碼：

public class GetResourcesSample {
    private static final String MAIN_FILE = "main-resources-file.txt";
    private static final String MAIN_FILE_WITH_SLASH = "/main-resources-file.txt";
    private static final String TEST_FILE = "test-resources-file.txt";
    private static final String TEST_FILE_WITH_SLASH = "/test-resources-file.txt";
    
 
private static final String ROOT_FILE = "project-root-file.txt";
    private static final String ROOT_FILE_WITH_SLASH = "./project-root-file.txt";

    public static void main(String[] args) {
        validateResult(MAIN_FILE);
        validateResult(MAIN_FILE_WITH_SLASH);

        validateResult(TEST_FILE);
        validateResult(TEST_FILE_WITH_SLASH);

        validateResult(ROOT_FILE);
        validateResult(ROOT_FILE_WITH_SLASH);

    }

    
 
private static void validateResult(String file) {

        InputStream inputStream1 = GetResourcesSample.class.getClass().getResourceAsStream(file);
        if (inputStream1 != null) {
            System.out.println(MessageFormat
                    .format("GetResourcesSample.class.getClass().getResourceAsStream(\"{0}\") is not null!", file));
        }

        InputStream inputStream2 = GetResourcesSample.class.getResourceAsStream(file);
        if (inputStream2 != null) {
            System.out.println(
                    MessageFormat.format("GetResourcesSample.class.getResourceAsStream(\"{0}\") is not null!", file));
        }

        InputStream inputStream3 = GetResourcesSample.class.getClassLoader().getResourceAsStream(file);
        if (inputStream3 != null) {
            System.out.println(
                    MessageFormat.format("GetResourcesSample.class.getClassLoader().getResourceAsStream(\"{0}\") is not null!", file));
        }

    }
}

結果：

GetResourcesSample.class.getClassLoader().getResourceAsStream("main-resources-file.txt") is not null! GetResourcesSample.class.getClass().getResourceAsStream("/main-resources-file.txt") is not null! GetResourcesSample.class.getResourceAsStream("/main-resources-file.txt") is not null!

結論：

1. Class.getResourceAsStream 最終調用的是此Class的Class Loader的getResourceAsStream來進行讀文件（有些繞，盡量理解）
2. GetResourcesSample.class.getClass() 得到的是Class這個類的實例，它的ClassLoader是JVM的bootstrap Class Loader
3. GetResourcesSample.class.getResourceAsStream 由於去resolve了一下name，雖然是當前class的ClassLoader，它也讀不到這個文件；除非你的文件名以“／”開頭。詳見源代碼：

       /**
        * Add a package name prefix if the name is not absolute Remove leading "/"
        * if name is absolute
        */
       private String resolveName(String name) {
           if (name == null) {
               return name;
           }
           if (!name.startsWith("/")) {
               Class<?> c = this;
               while (c.isArray()) {
                   c = c.getComponentType();
               }
               String baseName = c.getName();
               int index = baseName.lastIndexOf(‘.‘);
               if (index != -1) {
                   name = baseName.substring(0, index).replace(‘.‘, ‘/‘)
                       +"/"+name;
               }
           } else {
               name = name.substring(1);
           }
           return name;
       }

4. project-root-file.txt這種最後最終不被打在Jar包裏的文件，是沒有機會被讀取的，除非hard code一個文件所在的絕對路徑
5. 把相同代碼放到UT裏面去跑，會發現UT能同時load到main和test下的文件。因為JUnit有它自己的ClassLoader，它能同時讀到main和test下的文件。

java踩坑記-getResourceAsStream