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Java 讀取外部資源的方法詳解
在Java代碼中經(jīng)常有讀取外部資源的要求:如配置文件等等,通常會(huì)把配置文件放在classpath下或者在web項(xiàng)目中放在web-inf下.
1.從當(dāng)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(gè)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(huì)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(xiàng)目從web-inf文件夾讀取(通過(guò)得到ServletContext讀取,可以在servlet或者能夠得到request的類(lèi)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(huán)境中運(yùn)行測(cè)試過(guò).不過(guò)最近在用JUnit的時(shí)候,通過(guò)ant運(yùn)行JUnit時(shí)通過(guò)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.
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