Java 读取外部资源的方法详解

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.

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