JAVA读取外部资源的方法

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.youkuaiyun.com/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.getSystemResourceAsStream用的是getSystemClassLoader，和Xclass.class.getClassLoader()是不同的，查找的路径不一样.