Write a file to resources folder in Spring

Question

I want to know, how to write a file to a resources folder in a Spring MVC project. I defined the resources path in a web-dispatcher-servlet.xml as
<mvc:resources mapping="/resources/**" location="/resources/" />

I read examples about how to read a file from a resources folder. But I want to write a file to a resources folder. I tried

ClassLoader classLoader = getClass().getClassLoader();
    File file = new File(classLoader.getResource("file/test.xml").getFile());
    if (file.createNewFile()) {
        System.out.println("File is created!");
    } else {
        System.out.println("File already exists.");
    }

But I get a
Request processing failed; nested exception is java.lang.NullPointerException

Answer 1

If you want to create a test.xml file in the directory returned by getResource(), try this:

File file = new File(classLoader.getResource(".").getFile() + "/test.xml");
if (file.createNewFile()) {
    System.out.println("File is created!");
} else {
    System.out.println("File already exists.");
}

Calling getFile() on a non-existent directory or file will return null, as explained in Reid's answer.

Answer 2

It looks like your call to getResource("file/test.xml") is likely returning null.

I'm curious, what is the full path to your XML file? For this to work, the resources directory needs to be placed in your webapp directory. If you are trying to use the standard Java resources structure (src/main/resources) then that Spring MVC mapping will not work.

EDIT: After seeing your answer to @Ascalonian's comment, this will not work since the file doesn't exist. Like I mentioned earlier, getResource("file/test.xml") will return null so the following call to getFile() will throw the NPE. Maybe you should check if getResource returns null and use that as an indication that the file needs to be created.

Answer 3

Firstly, you should not write to a file in resource folder, as it will get deleted whenever you do a fresh build. Instead store it in some other location and specify the path in a property file.

You can use the following way to create a file :

String rootPath = System.getProperty("user.dir");
File file = new File(StringUtils.join(rootPath, "/any/path/from/your/project/root/directory/" , "test.xml"));
//Below commented line is what you wish to do. But I recommend not to do so.
//File file = new File(StringUtils.join(rootPath, "/out/resources/file/" , "test.xml"));
file.createNewFile();