您可以使用 System 类加载器在引导类路径上查找类。例如,这个
System.out.println(
ClassLoader.getSystemClassLoader().getResource("java/lang/String.class")
);
会打印出类似的东西,
jar:file:/C:/Program%20Files/Java/jdk1.6.0_22/jre/lib/rt.jar!/java/lang/String.class
要查找MyClass.class
磁盘上的位置,请执行
String urlString = ClassLoader
.getSystemClassLoader()
.getResource("com/my/package/MyClass.class")
.toString();
urlString = urlString.substring(urlString.indexOf("file:"), urlString.indexOf('!'));
URL url = new URL(urlString);
File file = new File(url.toURI());
System.out.println(file);
System.out.println(file.exists());
kriegaex于2020-06-29更新:我不想为这个老问题写一个新的答案,而是想增强或更新这个非常好的答案,同时考虑到带有空格和 Java 9+ 模块的路径。
这是一个将类文件路径作为File
实例返回的方法。如果类文件是 JAR 或 Java 运行时模块的一部分(URL 以 protocol 开头jrt:
),它只会返回 JAR 或 JMOD 文件的路径,这可能是您不想要的,但这只是一个展示,您可以随心所欲地编辑。当然,这仍然是 hacky,例如,不考虑从 Web URL 而不是从文件加载的类,但你明白了。
public static File getFileForClass(String className) {
className = className.replace('.', '/') + ".class";
URL classURL = ClassLoader.getSystemClassLoader().getResource(className);
if (classURL == null)
return null;
System.out.println("Class file URL: " + classURL);
// Adapt this if you also have '.war' or other archive types
if (classURL.toString().contains(".jar!")) {
String jarFileName = classURL.getPath().replaceFirst("!.*", "");
System.out.println("Containing JAR file: " + jarFileName);
try {
return new File(new URL(jarFileName).toURI());
}
catch (URISyntaxException | MalformedURLException e) {
throw new RuntimeException(e);
}
}
if (classURL.getProtocol().equals("jrt")) {
String jrtModule = classURL.getFile().replaceFirst("/([^/]+).*", "$1");
System.out.println("Target class is part of Java runtime module " + jrtModule);
String jmodName = System.getProperty("java.home") + "/jmods/" + jrtModule + ".jmod";
System.out.println("Containing Java module file: " + jmodName);
return new File(jmodName);
}
try {
return new File(classURL.toURI());
}
catch (URISyntaxException e) {
throw new RuntimeException(e);
}
}
当我从我的一个 IntelliJ IDEA 项目中调用它时,JDK 14 安装在一个包含空格的路径下,并故意添加一个 JAR 也包含一个带有空格的路径以进行测试,这段代码......
public static void main(String[] args) throws IOException {
Instrumentation instrumentation = ByteBuddyAgent.install();
instrumentation.appendToSystemClassLoaderSearch(
new JarFile("C:/Program Files/JetBrains/IntelliJ IDEA 2018.3/lib/idea_rt.jar")
);
Stream
.of(
Weaver.class.getName(),
String.class.getName(),
ByteBuddy.class.getName(),
"com.intellij.execution.TestDiscoveryListener"
)
.forEach(className -> System.out.printf("Found file: %s%n%n", getFileForClass(className)));
}
...产生这个控制台输出:
Class file URL: file:/C:/Users/alexa/Documents/java-src/Sarek/sarek-aspect/target/classes/dev/sarek/agent/aspect/Weaver.class
Found file: C:\Users\alexa\Documents\java-src\Sarek\sarek-aspect\target\classes\dev\sarek\agent\aspect\Weaver.class
Class file URL: jrt:/java.base/java/lang/String.class
Target class is part of Java runtime module java.base
Containing Java module file: C:\Program Files\Java\jdk-14.0.1/jmods/java.base.jmod
Found file: C:\Program Files\Java\jdk-14.0.1\jmods\java.base.jmod
Class file URL: jar:file:/C:/Users/alexa/.m2/repository/net/bytebuddy/byte-buddy/1.10.13/byte-buddy-1.10.13.jar!/net/bytebuddy/ByteBuddy.class
Containing JAR file: file:/C:/Users/alexa/.m2/repository/net/bytebuddy/byte-buddy/1.10.13/byte-buddy-1.10.13.jar
Found file: C:\Users\alexa\.m2\repository\net\bytebuddy\byte-buddy\1.10.13\byte-buddy-1.10.13.jar
Class file URL: jar:file:/C:/Program%20Files/JetBrains/IntelliJ%20IDEA%202018.3/lib/idea_rt.jar!/com/intellij/execution/TestDiscoveryListener.class
Containing JAR file: file:/C:/Program%20Files/JetBrains/IntelliJ%20IDEA%202018.3/lib/idea_rt.jar
Found file: C:\Program Files\JetBrains\IntelliJ IDEA 2018.3\lib\idea_rt.jar