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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