Java: URL.getPath() of current “main” class returns “null”, why?
I'm trying to print the current path of class that executes main(), as below. I found the statements below from googling, but doesn't work in my computer(windows+intellij)
public class core3 {
public static void main(String args) {
try {
URL url = new core3().getClass().getClassLoader().getResource("");
System.out.println(url);
System.out.println(System.getProperty(url.getPath()));//print null
} catch (Exception e) {
e.printStackTrace();
}
}
}
Actually it prints
file:/D:/Documents/myproject/test01/target/classes/
null
Why the second print returns null? How to fix it?
Thanks
java class url path main
asked Nov 24 '18 at 9:49
TroskyvsTroskyvs
2,33821029
add a comment |
I'm trying to print the current path of class that executes main(), as below. I found the statements below from googling, but doesn't work in my computer(windows+intellij)
public class core3 {
public static void main(String args) {
try {
URL url = new core3().getClass().getClassLoader().getResource("");
System.out.println(url);
System.out.println(System.getProperty(url.getPath()));//print null
} catch (Exception e) {
e.printStackTrace();
}
}
}
Actually it prints
file:/D:/Documents/myproject/test01/target/classes/
null
Why the second print returns null? How to fix it?
Thanks
java class url path main
asked Nov 24 '18 at 9:49
TroskyvsTroskyvs
2,33821029
Why do expect for system properties to contain that path?
– user10639668
Nov 24 '18 at 10:02
add a comment |
I'm trying to print the current path of class that executes main(), as below. I found the statements below from googling, but doesn't work in my computer(windows+intellij)
public class core3 {
public static void main(String args) {
try {
URL url = new core3().getClass().getClassLoader().getResource("");
System.out.println(url);
System.out.println(System.getProperty(url.getPath()));//print null
} catch (Exception e) {
e.printStackTrace();
}
}
}
Actually it prints
file:/D:/Documents/myproject/test01/target/classes/
null
Why the second print returns null? How to fix it?
Thanks
java class url path main
asked Nov 24 '18 at 9:49
TroskyvsTroskyvs
2,33821029
I'm trying to print the current path of class that executes main(), as below. I found the statements below from googling, but doesn't work in my computer(windows+intellij)
public class core3 {
public static void main(String args) {
try {
URL url = new core3().getClass().getClassLoader().getResource("");
System.out.println(url);
System.out.println(System.getProperty(url.getPath()));//print null
} catch (Exception e) {
e.printStackTrace();
}
}
}
Actually it prints
file:/D:/Documents/myproject/test01/target/classes/
null
Why the second print returns null? How to fix it?
Thanks
java class url path main
java class url path main
asked Nov 24 '18 at 9:49
TroskyvsTroskyvs
2,33821029
asked Nov 24 '18 at 9:49
TroskyvsTroskyvs
2,33821029
asked Nov 24 '18 at 9:49
TroskyvsTroskyvs
2,33821029
asked Nov 24 '18 at 9:49
TroskyvsTroskyvs
2,33821029
asked Nov 24 '18 at 9:49
TroskyvsTroskyvs
2,33821029
2,33821029
Why do expect for system properties to contain that path?
– user10639668
Nov 24 '18 at 10:02
add a comment |
Why do expect for system properties to contain that path?
– user10639668
Nov 24 '18 at 10:02
Why do expect for system properties to contain that path?
– user10639668
Nov 24 '18 at 10:02
Why do expect for system properties to contain that path?
– user10639668
Nov 24 '18 at 10:02
add a comment |
2 Answers
2
active
oldest
votes
System.getProperty() is for getting system properties. For example, the "java.home" system property typically points to the location of your Java installation. System properties are described here.
Your code is looking up a system property with key equal to your URL. You do not have such a system property defined, so System.getProperty() returns null.
If you just want to print the path, you should simply omit the System.getProperty() call:
System.out.println(url.getPath());
answered Nov 24 '18 at 9:54
AutoAnswererAutoAnswerer
284
add a comment |
Why the second print returns null?
Because you are attempting to lookup a system property that doesn't exist.
This is not the way to find the path for the Main class.
What you need to do is:
Obtain the fully qualified (or canonical) name for the class; e.g.
String name = Main.class.getCanonicalName();
Map that to the resource path for the ".class" file. You need to:
- replace all "." characters in full classname with "/", and then
- append ".class".
Use
getResource(resourcePath)to lookup theURL.
If the resulting URL is a "file:" URL, you can then use URL::toFile() to get the pathname in the file system.
But if the URL is a "jar:" URL (as it will be if you loaded the class from a JAR file) the the class will not have a file system pathname.
Note that getClassLoader().getResource("") gives you the path for the classloader's root directory. That's not the path for the original class.
And if you want the name of the JVM class that calls your static void main(String) method, then you should be able to get this using the Java 9+ StackWalker class (javadoc). You will need to use the option to show the hidden frames, I think.
answered Nov 24 '18 at 10:11
Stephen CStephen C
515k69563920
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
System.getProperty() is for getting system properties. For example, the "java.home" system property typically points to the location of your Java installation. System properties are described here.
Your code is looking up a system property with key equal to your URL. You do not have such a system property defined, so System.getProperty() returns null.
If you just want to print the path, you should simply omit the System.getProperty() call:
System.out.println(url.getPath());
answered Nov 24 '18 at 9:54
AutoAnswererAutoAnswerer
284
add a comment |
System.getProperty() is for getting system properties. For example, the "java.home" system property typically points to the location of your Java installation. System properties are described here.
Your code is looking up a system property with key equal to your URL. You do not have such a system property defined, so System.getProperty() returns null.
If you just want to print the path, you should simply omit the System.getProperty() call:
System.out.println(url.getPath());
answered Nov 24 '18 at 9:54
AutoAnswererAutoAnswerer
284
add a comment |
System.getProperty() is for getting system properties. For example, the "java.home" system property typically points to the location of your Java installation. System properties are described here.
Your code is looking up a system property with key equal to your URL. You do not have such a system property defined, so System.getProperty() returns null.
If you just want to print the path, you should simply omit the System.getProperty() call:
System.out.println(url.getPath());
answered Nov 24 '18 at 9:54
AutoAnswererAutoAnswerer
284
System.getProperty() is for getting system properties. For example, the "java.home" system property typically points to the location of your Java installation. System properties are described here.
Your code is looking up a system property with key equal to your URL. You do not have such a system property defined, so System.getProperty() returns null.
If you just want to print the path, you should simply omit the System.getProperty() call:
System.out.println(url.getPath());
answered Nov 24 '18 at 9:54
AutoAnswererAutoAnswerer
284
edited Nov 24 '18 at 10:02
answered Nov 24 '18 at 9:54
AutoAnswererAutoAnswerer
284
answered Nov 24 '18 at 9:54
AutoAnswererAutoAnswerer
284
answered Nov 24 '18 at 9:54
AutoAnswererAutoAnswerer
284
284
add a comment |
add a comment |
Why the second print returns null?
Because you are attempting to lookup a system property that doesn't exist.
This is not the way to find the path for the Main class.
What you need to do is:
Obtain the fully qualified (or canonical) name for the class; e.g.
String name = Main.class.getCanonicalName();
Map that to the resource path for the ".class" file. You need to:
- replace all "." characters in full classname with "/", and then
- append ".class".
Use
getResource(resourcePath)to lookup theURL.
If the resulting URL is a "file:" URL, you can then use URL::toFile() to get the pathname in the file system.
But if the URL is a "jar:" URL (as it will be if you loaded the class from a JAR file) the the class will not have a file system pathname.
Note that getClassLoader().getResource("") gives you the path for the classloader's root directory. That's not the path for the original class.
And if you want the name of the JVM class that calls your static void main(String) method, then you should be able to get this using the Java 9+ StackWalker class (javadoc). You will need to use the option to show the hidden frames, I think.
answered Nov 24 '18 at 10:11
Stephen CStephen C
515k69563920
add a comment |
Why the second print returns null?
Because you are attempting to lookup a system property that doesn't exist.
This is not the way to find the path for the Main class.
What you need to do is:
Obtain the fully qualified (or canonical) name for the class; e.g.
String name = Main.class.getCanonicalName();
Map that to the resource path for the ".class" file. You need to:
- replace all "." characters in full classname with "/", and then
- append ".class".
Use
getResource(resourcePath)to lookup theURL.
If the resulting URL is a "file:" URL, you can then use URL::toFile() to get the pathname in the file system.
But if the URL is a "jar:" URL (as it will be if you loaded the class from a JAR file) the the class will not have a file system pathname.
Note that getClassLoader().getResource("") gives you the path for the classloader's root directory. That's not the path for the original class.
And if you want the name of the JVM class that calls your static void main(String) method, then you should be able to get this using the Java 9+ StackWalker class (javadoc). You will need to use the option to show the hidden frames, I think.
answered Nov 24 '18 at 10:11
Stephen CStephen C
515k69563920
add a comment |
Why the second print returns null?
Because you are attempting to lookup a system property that doesn't exist.
This is not the way to find the path for the Main class.
What you need to do is:
Obtain the fully qualified (or canonical) name for the class; e.g.
String name = Main.class.getCanonicalName();
Map that to the resource path for the ".class" file. You need to:
- replace all "." characters in full classname with "/", and then
- append ".class".
Use
getResource(resourcePath)to lookup theURL.
If the resulting URL is a "file:" URL, you can then use URL::toFile() to get the pathname in the file system.
But if the URL is a "jar:" URL (as it will be if you loaded the class from a JAR file) the the class will not have a file system pathname.
Note that getClassLoader().getResource("") gives you the path for the classloader's root directory. That's not the path for the original class.
And if you want the name of the JVM class that calls your static void main(String) method, then you should be able to get this using the Java 9+ StackWalker class (javadoc). You will need to use the option to show the hidden frames, I think.
answered Nov 24 '18 at 10:11
Stephen CStephen C
515k69563920
Why the second print returns null?
Because you are attempting to lookup a system property that doesn't exist.
This is not the way to find the path for the Main class.
What you need to do is:
Obtain the fully qualified (or canonical) name for the class; e.g.
String name = Main.class.getCanonicalName();
Map that to the resource path for the ".class" file. You need to:
- replace all "." characters in full classname with "/", and then
- append ".class".
Use
getResource(resourcePath)to lookup theURL.
If the resulting URL is a "file:" URL, you can then use URL::toFile() to get the pathname in the file system.
But if the URL is a "jar:" URL (as it will be if you loaded the class from a JAR file) the the class will not have a file system pathname.
Note that getClassLoader().getResource("") gives you the path for the classloader's root directory. That's not the path for the original class.
And if you want the name of the JVM class that calls your static void main(String) method, then you should be able to get this using the Java 9+ StackWalker class (javadoc). You will need to use the option to show the hidden frames, I think.
answered Nov 24 '18 at 10:11
Stephen CStephen C
515k69563920
edited Nov 24 '18 at 10:53
answered Nov 24 '18 at 10:11
Stephen CStephen C
515k69563920
answered Nov 24 '18 at 10:11
Stephen CStephen C
515k69563920
answered Nov 24 '18 at 10:11
Stephen CStephen C
515k69563920
515k69563920
add a comment |
add a comment |
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Why do expect for system properties to contain that path?
– user10639668
Nov 24 '18 at 10:02