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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