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This article mainly explains the "detailed introduction of getResource () in Java". The content of the explanation in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "the detailed introduction of getResource () in Java".

Description of running resources in Java

Here, we simply divide the resources available to running Java processes into two categories:

Resources that exist in the file system

Such resources generally exist directly on disk and can be accessed directly from the explorer. When we access such resources through the application, we can either use the File object to get it through the file system, or use the getResource () method to get it (only in classpath).

Note that the scope of the getResource () method is limited to resources outside the specified scope classpath,classpath that are not available.

Resources that exist in the jar package

Such resources, literally, exist in the jar package, while jar is included in the classpath. So this kind of resource can be properly called a resource in the code. Because this resource is contained in a file, we can only get the jar package with File, but not the resources in the jar package.

Such resources are generally files that exist in classpath, and we can use the getResource () method above to get its path (usually the style is the path of the file where the resource is located + the path of the resource in the file), but there is no way to read it directly through the file. However, the input stream of the resource can be obtained through the getResourceAsStream () method in the classLoader object.

GetResource () description in Java

There is a getResource () method in a class object such as java.lang.String.class or a concrete class loader object such as java.lang.String.class.getClassLoader () in Java, but when calling the getResource () method on a class object, the path is different from calling the getResource () method on a class loader object.

When the path passed in the getResource () method is absolute, both start looking for resources from classpath:

Main.class.getResource ("/ com/ghimi/demo/data.json"); Main.class.getClassLoader () .g

When the path passed in the getResource () method is relative, the way they look for resources will be different.

/ / when using a class object to load a resource, it will look for the resource from the class object directory / / for example, the Main.class is located in the / com/ghimi/demo directory of the demo01.jar package / / the getResource method will try to find the data.json resource Main.class.getResource ("data.json") from this directory. / / when a resource is loaded using a classloader object, the resource is looked up from the classpath root directory / / the getResource method attempts to find the data.json resource Main.class.getClassLoader () .getResource ("data.json") from the classpath root directory.

When the getResource () method cannot get the resource, it returns null.

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