Java讀取外部資源的方法

在Java代碼中經常有讀取外部資源的要求:如配置文件等等,通常會把配置文件放在classpath下或者在web項目中放在web-inf下.

1.從當前的工作目錄中讀取:

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,從classpath中讀取(讀取找到的第一個符合名稱的文件):

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,從classpath中讀取(讀取找到的所有符合名稱的文件,如spring中帶有classpath*:前綴的情況就會從classpath中遍歷):

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,從URL中讀取:

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項目從web-inf文件夾讀取(通過得到ServletContext讀取,可以在servlet或者能夠得到request的類中使用):

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();
        }

 以上代碼在eclipse環境中運行測試過.不過最近在用JUnit的時候,通過ant運行JUnit時通過ClassLoader.getSystemResourceAsStream("file.txt");的方式去找不到文件.改成 Xclass.class.getClassLoader().getResourceAsStream("file.txt");能從ant指定的classpath中找到文件.原因是ClassLoader和Xclass.class.getClassLoader()是不同的,查找的路徑不一樣.