Resource Components of Spring

1.资源组件UML类图



资源组件接口中核心方法：exists(), isopen(), isReadable(), getInputStream()
引用核心的Java API：File类，URL类
2.重点介绍UrlResource和ClasspathResource
UrlResource
     利用统一资源标识符或者定位符加载资源，其中UrlResource封装了Url，UrlConnection的操作。持有Url，Uri等对象。UrlResource的exists(), isReadable()方法继承自父类AbstractResourceResolving。提供了利用Url变量得到文件File。用File类的方法操作资源，验证资源的可读性，是否存在，是否可被打开！通过UrlConnection获取资源的输入流！
例如：
public InputStream getInputStream()
throws IOException {

URLConnection con =
this.url.openConnection();

ResourceUtils.useCachesIfNecessary(con);
try {
return
con.getInputStream();

}
catch (IOException
ex) {
// Close the HTTP connection (if applicable).
if (con
instanceof HttpURLConnection) {

((HttpURLConnection) con).disconnect();

}
throw
ex;

}
}

ClassPathResource
此对象用来获取class path下的资源，其中ClassPathResource持有Class, ClassLoader等对象。利用Class和ClassLoader对象的getResource()和getResourceStream()方法操作资源，妥妥的！
例如：
判断资源是否存在
public
boolean exists() {
return (resolveURL() !=
null);
 }

protected URL resolveURL() {
if (this.clazz !=
null) {
return
this.clazz.getResource(this.path);

}
else
if (this.classLoader !=
null) {
return
this.classLoader.getResource(this.path);

}
else {
return ClassLoader.getSystemResource(this.path);

}
}

获取资源的输入流对象
public InputStream getInputStream()
throws IOException {

InputStream is;
if (this.clazz !=
null) {
is =
this.clazz.getResourceAsStream(this.path);

}
else
if (this.classLoader !=
null) {
is =
this.classLoader.getResourceAsStream(this.path);

}
else {
is = ClassLoader.getSystemResourceAsStream(this.path);

}
if (is ==
null) {
throw
new FileNotFoundException(getDescription() +
" cannot be opened because it does not exist");

}
return
is;
}