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Java读取外部资源的方法


 

   

  在java代码中经常有读取外部资源的要求:如配置文件等等,通常会把配置文件放在classpath下或者在web项目中放在web-inf下.

  1.从当前的工作目录中读取:

  try {

  BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream("wkdir.txt")));

  String str;

  while ((str = in.readLine()) != null) {

  System.out.println(str);

  }

  in.close();

  } catch (IOException e) {

  }

  2,从classpath中读取(读取找到的第一个符合名称的文件):

  try {

  InputStream stream = ClassLoader.getSystemResourceAsStream("fileinjar.txt");

  BufferedReader in = new BufferedReader(new InputStreamReader(stream));

  String str;

  while ((str = in.readLine()) != null) {

  System.out.println(str);

  }

  in.close();

  } catch (IOException e) {

  }

  3,从classpath中读取(读取找到的所有符合名称的文件,如Spring中带有classpath*:前缀的情况就会从classpath中遍历):

  try {

  Enumeration resourceUrls = Thread.currentThread().getContextClassLoader().getResources("fileinjar.txt");

  while (resourceUrls.hasMoreElements()) {

  URL url = (URL) resourceUrls.nextElement();

  System.out.println(url);

  BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));

  String str;

  while ((str = in.readLine()) != null) {

  System.out.println(str);

  }

  in.close();

  }

  } catch (IOException e) {

  }

  4,从URL中读取:

  try {

  URL url = new URL("http://blog.csdn.net/kkdelta");

  System.out.println(url);

  BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));

  String str;

  while ((str = in.readLine()) != null) {

  System.out.println(str);

  }

  in.close();

  } catch (IOException e) {

  e.printStackTrace();

  }

  5,web项目从web-inf文件夹读取(通过得到ServletContext读取,可以在servlet或者能够得到request的类中使用):

  try {

  URL url = (URL) getServletContext().getResource("/WEB-INF/webinffile.txt");

  // URL url = (URL)req.getSession().getServletContext().getResource("/WEB-INF/webinffile.txt");

  System.out.println(url);

  BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));

  String str;

  while ((str = in.readLine()) != null) {

  System.out.println(str);

  }

  in.close();

  } catch (IOException e) {

  e.printStackTrace();

  }

  以上代码在eclipse环境中运行测试过.不过最近在用JUnit的时候,通过ant运行JUnit时通过ClassLoader.getSystemResourceAsStream("file.txt");的方式去找不到文件.改成 Xclass.class.getClassLoader().getResourceAsStream("file.txt");能从ant指定的classpath中找到文件.原因是ClassLoader和Xclass.class.getClassLoader()是不同的,查找的路径不一样.