Java 读取外部资源的方法详解及实例代码

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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