可以“添加”吗？在java中动态地类路径？ [英] Is it possible to "add" to classpath dynamically in java?
问题描述
java -classpath ../classes;../jar;. parserTester
如何以编程方式获取上述命令中的功能？喜欢，是否可以运行：
How can i get the functionality in the above command programmatically? Like, is it possible to run as:
java parserTester
得到相同的结果？我尝试使用URLClassLoader但它修改了类路径并且没有添加它。
and get the same result? I tried using URLClassLoader but it modifies the classpath and does not add to it.
Thanx！
感谢Milhous的回应。但这就是我想要做的事情。如何才能让jar首先进入类路径？我也尝试使用自定义类加载器:(
Thanks for the response Milhous. But that is what i am trying to do.. How is it possible to get the jar into the classpath first? I tried using a custom classloader too :(
这有效..但很抱歉我需要只运行它：
java parserTester
I想知道这样的事情是否可能???
That works.. But sorry that i need to run it only as: java parserTester I would like to know if such a thing is possible???
它需要如此bcoz我将parserTester.java和.class放在一个单独的文件夹中。我需要保留文件结构.respeerTester在一个单独的jar文件夹中使用jar。
It needs to be so bcoz i have parserTester.java and .class in a separate folder. I need to retain the file structure. The parserTester makes use of a jar in a separate jar folder.
推荐答案
你可以使用java.net .URLClassLoader用任何程序定义的URL列表加载你想要的URL：
You can use a java.net.URLClassLoader to load classes with any program defined list of URL's you wish:
public class URLClassLoader
extends SecureClassLoader
public class URLClassLoader extends SecureClassLoader
此类加载器用于从引用JAR
文件和目录的URL的搜索
路径加载
类和资源。任何URL
以'/'结尾，假定引用
a目录。否则，URL为
，假定引用JAR文件，将根据需要打开
。
This class loader is used to load classes and resources from a search path of URLs referring to both JAR files and directories. Any URL that ends with a '/' is assumed to refer to a directory. Otherwise, the URL is assumed to refer to a JAR file which will be opened as needed.
当
随后加载类和
时，将使用创建
URLClassLoader实例的线程
的AccessControlContext资源。
The AccessControlContext of the thread that created the instance of URLClassLoader will be used when subsequently loading classes and resources.
加载的类是
默认授予权限仅
访问创建
URLClassLoader时指定的URL 。
The classes that are loaded are by default granted permission only to access the URLs specified when the URLClassLoader was created.
自：
1.2
Since: 1.2
有点花哨footwork可以扩展它以支持使用通配符的路径名来获取JAR的整个目录（这段代码有一些对实用程序方法的引用，但它们的实现应该在上下文中很明显）：
And a little fancy footwork can extend it to support using wildcarded pathnames to pick up entire directories of JARs (this code has some references to utility methods, but their implementation should be obvious in the context):
/**
* Add classPath to this loader's classpath.
* <p>
* The classpath may contain elements that include a generic file base name. A generic basename
* is a filename without the extension that may begin and/or end with an asterisk. Use of the
* asterisk denotes a partial match. Any files with an extension of ".jar" whose base name match
* the specified basename will be added to this class loaders classpath. The case of the filename is ignored.
* For example "/somedir/*abc" means all files in somedir that end with "abc.jar", "/somedir/abc*"
* means all files that start with "abc" and end with ".jar", and "/somedir/*abc*" means all files
* that contain "abc" and end with ".jar".
*
*/
public void addClassPath(String cp) {
String seps=File.pathSeparator; // separators
if(!File.pathSeparator.equals(";")) { seps+=";"; } // want to accept both system separator and ';'
for(StringTokenizer st=new StringTokenizer(cp,seps,false); st.hasMoreTokens(); ) {
String pe=st.nextToken();
File fe;
String bn=null;
if(pe.length()==0) { continue; }
fe=new File(pe);
if(fe.getName().indexOf('*')!=-1) {
bn=fe.getName();
fe=fe.getParentFile();
}
if(!fe.isAbsolute() && pe.charAt(0)!='/' && pe.charAt(0)!='\\') { fe=new File(rootPath,fe.getPath()); }
try { fe=fe.getCanonicalFile(); }
catch(IOException thr) {
log.diagln("Skipping non-existent classpath element '"+fe+"' ("+thr+").");
continue;
}
if(!GenUtil.isBlank(bn)) {
fe=new File(fe,bn);
}
if(classPathElements.contains(fe.getPath())) {
log.diagln("Skipping duplicate classpath element '"+fe+"'.");
continue;
}
else {
classPathElements.add(fe.getPath());
}
if(!GenUtil.isBlank(bn)) {
addJars(fe.getParentFile(),bn);
}
else if(!fe.exists()) { // s/never be due getCanonicalFile() above
log.diagln("Could not find classpath element '"+fe+"'");
}
else if(fe.isDirectory()) {
addURL(createUrl(fe));
}
else if(fe.getName().toLowerCase().endsWith(".zip") || fe.getName().toLowerCase().endsWith(".jar")) {
addURL(createUrl(fe));
}
else {
log.diagln("ClassPath element '"+fe+"' is not an existing directory and is not a file ending with '.zip' or '.jar'");
}
}
log.diagln("Class loader is using classpath: \""+classPath+"\".");
}
/**
* Adds a set of JAR files using a generic base name to this loader's classpath. See @link:addClassPath(String) for
* details of the generic base name.
*/
public void addJars(File dir, String nam) {
String[] jars; // matching jar files
if(nam.endsWith(".jar")) { nam=nam.substring(0,(nam.length()-4)); }
if(!dir.exists()) {
log.diagln("Could not find directory for Class Path element '"+dir+File.separator+nam+".jar'");
return;
}
if(!dir.canRead()) {
log.error("Could not read directory for Class Path element '"+dir+File.separator+nam+".jar'");
return;
}
FileSelector fs=new FileSelector(true).add("BaseName","EG",nam,true).add("Name","EW",".jar",true);
if((jars=dir.list(fs))==null) {
log.error("Error accessing directory for Class Path element '"+dir+File.separator+nam+".jar'");
}
else if(jars.length==0) {
log.diagln("No JAR files match specification '"+new File(dir,nam)+".jar'");
}
else {
log.diagln("Adding files matching specification '"+dir+File.separator+nam+".jar'");
Arrays.sort(jars,String.CASE_INSENSITIVE_ORDER);
for(int xa=0; xa<jars.length; xa++) { addURL(createUrl(new File(dir,jars[xa]))); }
}
}
private URL createUrl(File fe) {
try {
URL url=fe.toURI().toURL();
log.diagln("Added URL: '"+url.toString()+"'");
if(classPath.length()>0) { classPath+=File.pathSeparator; }
this.classPath+=fe.getPath();
return url;
}
catch(MalformedURLException thr) {
log.diagln("Classpath element '"+fe+"' could not be used to create a valid file system URL");
return null;
}
}
这篇关于可以“添加”吗？在java中动态地类路径？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
