Resources.getResourceAsStream("mybatis-config.xml")过程一

使用

inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            
sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

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解读

inputStream = Resources.getResourceAsStream("mybatis-config.xml");

getResourceAsStream-1

public static InputStream getResourceAsStream(String resource) throws IOException {
    return getResourceAsStream(null, resource);
  }

getResourceAsStream-2

public static InputStream getResourceAsStream(ClassLoader loader, String resource) throws IOException {
    InputStream in = classLoaderWrapper.getResourceAsStream(resource, loader);
    if (in == null) {
      throw new IOException("Could not find resource " + resource);
    }
    return in;
  }

这里就是通过ClassLoader获取资源

Resources中classLoaderWrapper定义

public class Resources {
// classLoader的封装
  private static ClassLoaderWrapper classLoaderWrapper = new ClassLoaderWrapper();

ClassLoaderWrapper

public class ClassLoaderWrapper {

  ClassLoader defaultClassLoader;
  ClassLoader systemClassLoader;

  ClassLoaderWrapper() {
    try {
      systemClassLoader = ClassLoader.getSystemClassLoader();
    } catch (SecurityException ignored) {
      // AccessControlException on Google App Engine   
    }
  }

就是声明2个ClassLoader 并初始化一个systemClassLoader另一个 不初始化

InputStream in = classLoaderWrapper.getResourceAsStream(resource, loader);这个方法

 public InputStream getResourceAsStream(String resource) {
    return getResourceAsStream(resource, getClassLoaders(null));
  }

getClassLoaders

  ClassLoader[] getClassLoaders(ClassLoader classLoader) {
    return new ClassLoader[]{
        classLoader,
        defaultClassLoader,
        Thread.currentThread().getContextClassLoader(),
        getClass().getClassLoader(),
        systemClassLoader};
  }

getClassLoaders方法获取一个ClassLoader数组

getResourceAsStream(resource, getClassLoaders(null));

 InputStream getResourceAsStream(String resource, ClassLoader[] classLoader) {
    for (ClassLoader cl : classLoader) {
      if (null != cl) {

        //将指定路径的资源文转换为流 
        InputStream returnValue = cl.getResourceAsStream(resource);

        //如果找不到就去根路径下找
        if (null == returnValue) {
          returnValue = cl.getResourceAsStream("/" + resource);
        }

        if (null != returnValue) {
          return returnValue;
        }
      }
    }
    return null;
  }

总结

inputStream = Resources.getResourceAsStream("mybatis-config.xml");
就是通过ClassLoader的方法将传入资源文件解析为指定流或者其它