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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