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This article mainly introduces the springboot getSpringFactoriesInstances source code example analysis, has a certain reference value, interested friends can refer to, I hope you can learn a lot after reading this article, the following let Xiaobian take you to understand.

I. Overview and flow chart

In the springboot startup process, the getSpringFactoriesInstances method is very important. When starting, we use this method to find the corresponding META-INF/spring.factorys property files from all the jar packages on the classpath, and load and instantiate the initializers and listeners in it for further initialization work. The workflow flow chart is as follows:

Image II. Source code parsing

Let's follow the flow chart and sequence diagram to get a peek at the secret step by step:

Image calls the getSpringFactoriesInstances () method public SpringApplication (ResourceLoader resourceLoader, Class...) PrimarySources) {

/ / Resource loader

This.resourceLoader = resourceLoader

/ / assert that the input parameter cannot be empty, that is, the startup class must be passed in

Assert.notNull (primarySources, "PrimarySources must not be null")

This.primarySources = new LinkedHashSet (Arrays.asList (primarySources))

/ / infer the service type through the classpath

This.webApplicationType = WebApplicationType.deduceFromClasspath ()

/ / 1. Load the initializer and instantiate, 10. And assign a value to initializers

SetInitializers ((Collection) getSpringFactoriesInstances (ApplicationContextInitializer.class))

/ / same as above, listener

SetListeners ((Collection) getSpringFactoriesInstances (ApplicationListener.class))

/ / infer the application main class

This.mainApplicationClass = deduceMainApplicationClass ()

}

Get the class loader and call the loadFactoryNames () method and initialize the returned results and sort private Collection getSpringFactoriesInstances (Class type) {

Return getSpringFactoriesInstances (type, new Class [] {})

}

Private Collection getSpringFactoriesInstances (Class type, Class [] parameterTypes, Object... Args) {

/ / 2. Get class loader

ClassLoader classLoader = getClassLoader ()

/ / Use names and ensure unique to protect against duplicates

/ / 3. Call the loadFactoryNames method and use set to de-reprocess the returned result

Set names = new LinkedHashSet (SpringFactoriesLoader.loadFactoryNames (type, classLoader))

/ / 9. Instantiate initializer

List instances = createSpringFactoriesInstances (type, parameterTypes, classLoader, args, names)

/ / 9. Sort the instantiated results

AnnotationAwareOrderComparator.sort (instances)

Return instances

}

/ / this method mainly instantiates the initializer through reflection

Private List createSpringFactoriesInstances (Class type, Class [] parameterTypes

ClassLoader classLoader, Object [] args, Set names) {

List instances = new ArrayList (names.size ())

For (String name: names) {

Try {

Class instanceClass = ClassUtils.forName (name, classLoader)

Assert.isAssignable (type, instanceClass)

Constructor constructor = instanceClass.getDeclaredConstructor (parameterTypes)

T instance = (T) BeanUtils.instantiateClass (constructor, args)

Instances.add (instance)

}

Catch (Throwable ex) {

Throw new IllegalArgumentException ("Cannot instantiate" + type + ":" + name, ex)

}

}

Return instances

}

Query cache and read the key-value value of the META-INFO/spring.factorys file, and process the value value public static List loadFactoryNames (Class factoryClass, @ Nullable ClassLoader classLoader) {

String factoryClassName = factoryClass.getName ()

/ / returns the value of the initializer

Return loadSpringFactories (classLoader) .getOrDefault (factoryClassName, Collections.emptyList ())

}

Private static Map loadSpringFactories (@ Nullable ClassLoader classLoader) {

MultiValueMap result = / / query cache, return if there is any, and load if not

Cache.get (classLoader)

If (result! = null) {

Return result

}

Try {

/ / load all the file resource paths containing META-INFO/spring.factorys in the jar package through the classloader

Enumeration urls = (classLoader! = null?

ClassLoader.getResources (FACTORIES_RESOURCE_LOCATION):

ClassLoader.getSystemResources (FACTORIES_RESOURCE_LOCATION))

Result = new LinkedMultiValueMap ()

While (urls.hasMoreElements ()) {

URL url = urls.nextElement ()

UrlResource resource = new UrlResource (url)

/ / instantiate the properties object and load the contents of the spring.factorys file in the path

Properties properties = PropertiesLoaderUtils.loadProperties (resource)

For (Map.Entry entry: properties.entrySet ()) {

String factoryClassName = (String)

/ / get the key value

Entry.getKey (). Trim ()

/ / A pair of value values can be easily split.

For (String factoryName: StringUtils.commaDelimitedListToStringArray ((String) entry.getValue () {

/ / store key and value values in result result.add (factoryClassName, factoryName.trim ())

}

}

}

/ / store the result in the cache

Cache.put (classLoader, result)

Return result

}

Catch (IOException ex) {

Throw new IllegalArgumentException ("Unable to load factories from location [" +)

FACTORIES_RESOURCE_LOCATION + "]", ex)

}

} Thank you for reading this article carefully. I hope the article "sample Analysis of getSpringFactoriesInstances Source Code in springboot" shared by the editor will be helpful to you. At the same time, I also hope you will support us and pay attention to the industry information channel. More related knowledge is waiting for you to learn!

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