为什么执行时不能读取/ src / main / resources下的文件？

Question

I have a Java project and used the standard maven archetype to create the dir structure. It looks like this:

|-src/main/java 
|-src/main/resources
|-target/classes
|- ... 

Now one of my classes uses a .properties file to read in some settings. I placed it in src/main/resources and read it through File propertiesFile = new File("./src/main/resources/starter.properties"); .
When I use the eclipse run-configuration, everything works fine. But recently I tried to start the same Java-class from my console using java some.package.Class , and since the .class-file is located in target/classes I got the message, that ./src/main/resources/starter.properties couldn't be found.

What am I doing wrong? Is the .properties file not supposed to be located in the resources-folder or do I have to use an other way to load it?

Answer 1

The two previous answers are correct, but I wanted to give a bit more context.

This file is in two places. It starts off in /src/main/resources and when you build the project, Maven copies it to /target/classes.

At runtime, you shouldn't access the copy that is in your source code. Otherwise, your software would need access to the source code in order to run. Rather, you should access the copy that is in your deliverable. At execution time, you can safely assume that you will find it on the classpath. It's in the same place as your compiled classes, so if it weren't on the classpath, you wouldn't have been able to run the program in the first place. This is why you should use getResourceAsStream() as mentioned by the other answerers.

(Though for production software, I do recommend Spring's Resource abstraction for accessing these kinds of things.)

Answer 2

采用

YourClass.class.getResourceAsStream("/filename.properties");

Answer 3

To expand on the two answers already given, when you build your Maven project the files in src/main/resources are copied into your JAR at the root of the classpath. If you did a jar tvf *yourjarname* you would notice there is neither a src/main/java or src/main/resources folder in it. So trying to manually read from those (now non-existent) paths will fail when you run via JAR. The other two answers have excellent suggestions, use the getResourceAsStream method to read in your file. Theres even a method on the Properties object that makes this very convenient and easy to use:

     URL resourceURL = Thread.currentThread().getContextClassLoader()
           .getResource(yourpropertyfilename);

     Properties props = new Properties();
     props.load(resourceURL.openStream());

Answer 4

At runtime this file will be in your classpath. Use Class.getResourceAsStream() to access it.