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:

[java] view
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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
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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
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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
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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
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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.

6.项目中看到的 ，可以将格式json格式的文件转换成对象，然后在取值
InputStream

src
= H4csUtil.class.getResourceAsStream("/dsRouter.json");
MappingIterator<DsRouterRec>

iter
=
new
ObjectMapper().reader(DsRouterRec.class)
.readValues(src);

while
(iter.hasNext()) {
DsRouterRec

rec
=
iter.next();

if
(rec.getCat() !=

null
&&
rec.getCat().equals(H4csConstants.CENTER))
{

if
(rec.getStorecodes() !=

null
&&
rec.getStorecodes().contains(storeCode))
{

return
true;
}
}
}

return
false;

dsRouter.json文件[
{
"cat":

"CENTER",
"url":

"*********8",
"username":

"h4cs",
"password":

"h4cs",
"storecodes":

[
"0103",
"0105",
"0106"
]
},
{
"cat":

"HDPOS",
"url":

"**************",
"username":

"h4cs",
"password":

"h4cs",
"storecodes":

[
"0104"
]
}
]