Problem description

In the development process, we often encounter the situation of obtaining resource files in the code, and I recently encountered a problem when migrating the original Tomcat native project to the SpringBoot project, is that when running locally, obtaining local XML resource files can be obtained. However, when the project is executed as a WAR package and then deployed to Tomcat, a problem occurs and the resource file cannot be found. Then, after searching, it was determined that the following code failed to obtain the path through the ClassLoader.

ExcelXmlModelFactory.class.getClassLoader().getResource("template/").getPath()

Copy the code

My resource file is stored in the following path

On the local PC, the log path is

/Users/hupengfei/git/lap/lap-service/out/production/resources/template

Copy the code

However, when deploying SpringBoot as a WAR package to Tomcat, the printed directory is

/ home/app/lap/app/lap - service - 1.0.0 - the SNAPSHOT. The war! /WEB-INF/classes! /template/Copy the code

As you can see, you can’t directly access unextracted files in Linux, so you won’t find the files.

The solution

This is obtained by obtaining its stream from the getResourceAsStream() method of the ClassLoader

To read files inside the JAR, we can only use stream to read, not File

There are two ways to get resources

Reading configuration files is a common problem encountered during development, and there are two ways to read configuration files. Class.getresource (String Path), classLoader.getResource (String Path), classloader.getResource (String Path), classloader.getResource (String Path)

Class.getResource

  • The path to/Start: is fetched from the ClassPath root
  • The path is not to/Start: The default is to fetch resources from the package in which this class resides

Here’s an example

public class Test {
    public static void main(String[] args) {
    	 System.out.println(Test.class.getResource("/"));
        System.out.println(Test.class.getResource("")); }}Copy the code

The output is as follows

file:/Users/hupengfei/git/Test/out/production/classes/
file:/Users/hupengfei/git/Test/out/production/classes/Practice/Day13/
Copy the code

So if you have three resource files under resource

So how do I get these three files, because the directory structure in the class folder is as follows

-- classes
	-- Convience
	-- Practice
	-- Test
Copy the code

So if you want to get the resource file under Test, you can do the following

System.out.println(Test.class.getResource(".. /.. /Test/1.xml"));
System.out.println(Test.class.getResource("/Test/1.xml"));
Copy the code

ClassLoader.getResource

The path of classloader. getResource cannot start with a slash (/). Path is read from the root directory by default

Examples are as follows

System.out.println(Test.class.getClassLoader().getResource(""));
System.out.println(Test.class.getClassLoader().getResource("/"));
Copy the code

Print the following

file:/Users/hupengfei/git/Test/out/production/classes/
null
Copy the code

We can see from the example above

Test.class.getClassLoader().getResource("")=Test.class.getResource("/")

The difference between two get resource files

You can actually see this in class.getResource

	public java.net.URL getResource(String name) {
        name = resolveName(name);
        ClassLoader cl = getClassLoader0();
        if (cl==null) {
            // A system class.
            return ClassLoader.getSystemResource(name);
        }
        return cl.getResource(name);
    }

Copy the code

Classloader. getResource () {path ();} path () {path () {path ();}}};

    private String resolveName(String name) {
        if (name == null) {
            return name;
        }
        if(! name.startsWith("/")) { Class<? > c = this;while (c.isArray()) {
                c = c.getComponentType();
            }
            String baseName = c.getName();
            int index = baseName.lastIndexOf('. ');
            if(index ! = -1) { name = baseName.substring(0, index).replace('. '.'/')
                    +"/"+name; }}else {
            name = name.substring(1);
        }
        return name;
    }

Copy the code

And you can see what goes in here is alpha/alpha

Is from the

Refer to the article

  • www.cnblogs.com/yejg1212/p/…
  • Blog.csdn.net/xiaoxudong6…