JAVA读取外部资源的方法

本文转自：http://blog.csdn.net/kkdelta/article/details/5560210

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:

[java] view plaincopyprint?

1. try {  
2.             BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream("wkdir.txt")));  
3.             String str;  
4.             while ((str = in.readLine()) != null) {  
5.                 System.out.println(str);  
6.             }  
7.             in.close();  
8.         } catch (IOException e) {  
9.         }  

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):

[java] view plaincopyprint?

1. try {  
2.             InputStream stream = ClassLoader.getSystemResourceAsStream("fileinjar.txt");  
3.             BufferedReader in = new BufferedReader(new InputStreamReader(stream));  
4.             String str;  
5.             while ((str = in.readLine()) != null) {  
6.                 System.out.println(str);  
7.             }  
8.             in.close();  
9.         } catch (IOException e) {  
10.         }  

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):

[java] view plaincopyprint?

1. try {  
2.   
3.             Enumeration resourceUrls = Thread.currentThread().getContextClassLoader().getResources("fileinjar.txt");  
4.   
5.             while (resourceUrls.hasMoreElements()) {  
6.                 URL url = (URL) resourceUrls.nextElement();  
7.                 System.out.println(url);  
8.   
9.                 BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));  
10.                 String str;  
11.                 while ((str = in.readLine()) != null) {  
12.                     System.out.println(str);  
13.                 }  
14.                 in.close();  
15.   
16.             }  
17.   
18.         } catch (IOException e) {  
19.         }  

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:

[java] view plaincopyprint?

1. try {  
2.   
3.             URL url = new URL("http://blog.csdn.net/kkdelta");  
4.             System.out.println(url);  
5.   
6.             BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));  
7.             String str;  
8.             while ((str = in.readLine()) != null) {  
9.                 System.out.println(str);  
10.             }  
11.             in.close();  
12.   
13.         } catch (IOException e) {  
14.             e.printStackTrace();  
15.         }  

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):

[java] view plaincopyprint?

1. try {  
2.   
3.             URL url = (URL) getServletContext().getResource("/WEB-INF/webinffile.txt");  
4.             // URL url = (URL)req.getSession().getServletContext().getResource("/WEB-INF/webinffile.txt");  
5.             System.out.println(url);  
6.   
7.             BufferedReader in = new BufferedReader(new InputStreamReader(url.openStream()));  
8.             String str;  
9.             while ((str = in.readLine()) != null) {  
10.                 System.out.println(str);  
11.             }  
12.             in.close();  
13.   
14.         } catch (IOException e) {  
15.             e.printStackTrace();  
16.         }  

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.