如何在Linux中设置CLASSPATH让java找到jar文件？
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How to set CLASSPATH in Linux to let java find jar file?
提问by Alex
Under Linux I am trying to run a jar file as follows:
在 Linux 下，我试图运行一个 jar 文件，如下所示：
java -jar plantuml.jar -testdot
while having CLASSPATHset to any of the following (the file is located at /home/user/plantuml.jar):
同时CLASSPATH设置为以下任何一项（文件位于/home/user/plantuml.jar）：
export CLASSPATH=/home/user
export CLASSPATH=/home/user/
export CLASSPATH=/home/user/plantuml.jar
In either case, no matter how I define CLASSPATH, the javacommand gives an error Unable to access jarfile plantuml.jar. What am I doing wrong here?
在任何一种情况下，无论我如何定义CLASSPATH，java命令都会给出错误Unable to access jarfile plantuml.jar。我在这里做错了什么？
采纳答案by Uwe Plonus
You have to supply the complete path after the parameter -jar. So for your example you have to call
您必须在参数后提供完整路径-jar。所以对于你的例子，你必须打电话
java -jar /home/user/plantuml.jar -testdot
The $CLASSPATHis only evaluated to find additional files (classes/resources) but not the jar file defined in the command line.
该$CLASSPATH只计算发现其他文件（类/资源），而不是在命令行中定义的jar文件。
回答by Rajesh J Advani
The classpath is used to find classes when you refer to them by name. It's essentially a list of paths (directories AND jar/zip files) where the JVM needs to look for classes, or other resources when using methods like ClassLoader.getResourceAsStream().
当您按名称引用类时，类路径用于查找类。它本质上是一个路径列表（目录和 jar/zip 文件），JVM 在使用ClassLoader.getResourceAsStream().
The value passed to the -jar option on the command line is the file-path to the JAR file.
传递给命令行上 -jar 选项的值是 JAR 文件的文件路径。
So, it won't find a jar file if you are only referring to the jar file by name. The JAR file path in the CLASSPATH is supposed to be a path element that 'contains' other resources.
因此，如果您仅按名称引用 jar 文件，它将找不到 jar 文件。CLASSPATH 中的 JAR 文件路径应该是“包含”其他资源的路径元素。
What you need to do here, is either
您需要在这里做的是
- Provide the full path to the jar file when trying to execute the jar
- Set the classpath to the jar file's path, and run the java command giving the name of the main class you want to execute.
- 尝试执行 jar 时提供 jar 文件的完整路径
- 将类路径设置为 jar 文件的路径，然后运行 java 命令，给出要执行的主类的名称。
回答by Beata Gellner
Maybe you are missing name of the main class or path to the jar. Have you tried execute it:
也许您缺少主类的名称或 jar 的路径。你有没有试过执行它：
java -jar full_path/plantuml.jar package.YourClass -testdot
Is your program depending on other classes? If yes you might want to add -cp parameter.
你的程序是否依赖于其他类？如果是，您可能需要添加 -cp 参数。
回答by Soham Krishna Paul
export CLASSPATH="/path/to/class_or_jar1":"/path/to/class_or_jar2":"${CLASSPATH}"
