SoFunction
Updated on 2025-03-04

Detailed explanation of the source code API mechanism for file parsing

introduction

Spring Boot is an open source framework for quickly building applications based on Spring framework. It greatly simplifies the development and deployment process of Spring applications through features such as automatic configuration, starting dependency and embedded servers. This article will explore the background history, business scenarios, functional points and underlying principles of Spring Boot in depth, and simulate the startup process of Spring Boot through Java code handwriting, especiallyThe source code API mechanism for parsing files.

1. Background history of Spring Boot

1.1 The Origin and Development of Spring Boot

Spring Boot is a framework developed by the Pivotal team. It is based on the Spring framework and aims to simplify the development and deployment of Spring applications. Spring Boot was first released in 2014. Its original design was designed to deal with the frequent configuration redundancy and duplicate code problems in complex enterprise-level application development.

The development history of Spring Boot can be divided into several key stages:

  • Early Development (2013-2014): Spring Boot started development, and released version 1.0.0 in April 2014, introducing core features such as automatic configuration, start-up dependencies and command line interface (CLI).
  • Rapid development (2015-2017): Spring Boot has released multiple versions, constantly introducing new features and improvements, such as enhancement of Actuator, better testing support, etc., which has gradually become a popular framework in the Java development field.
  • Maturity and wide application (2018 to present): Spring Boot continues to update and improve small versions to adapt to changing technical needs, and plays an important role in cloud-native application development, containerized deployment, etc.

1.2 The core features of Spring Boot

The core features of Spring Boot can be summarized as follows:

  • Automatic configuration: Automatically configure Spring applications based on the dependencies and environment in the classpath to reduce the workload of manual configuration.
  • Starting dependency: Provide a series of starting dependencies to simplify dependencies in the project.
  • Embed server: Built-in servers such as Tomcat, Jetty or Undertow, and the application can be run directly without an external server.
  • Production ready: Provides monitoring, health checks, external configuration and other functions to enable applications to run smoothly in the production environment.

2. Spring Boot's business scenarios and functional points

2.1 Business scenarios

Spring Boot is suitable for a variety of business scenarios, including but not limited to:

  • Microservice architecture: Spring Boot can quickly create standalone, independently deployable microservice applications.
  • RESTful API Development: Provides rich support and simplified tools and features to develop RESTful APIs.
  • Web Application Development: Support the development of various web applications, such as single page applications, multi-page applications, websites, etc.
  • Batch Application: Provides support for batch applications, including task scheduling, processing of large data volumes, transaction management, etc.
  • Data access: Simplify integration with databases and other data sources, simplifying the development of the data access layer through automatic configuration and starting dependencies.

2.2 Functional Points

Spring Boot has a lot of functional points, and the following are some key functional points:

  • Automatic configuration: Automatically configure the application based on the dependencies and configuration files under the classpath.
  • Starting dependency: Provides a range of starting dependencies for the rapid introduction of common third-party libraries and frameworks.
  • Embed server: Built-in Tomcat, Jetty, Undertow and other servers, developers can package the application into executable JAR or WAR files and run it directly.
  • Monitoring and management: Provides some monitoring and management tools, such as Actuator module, to help developers monitor and manage the running status of applications in real time.
  • External configuration: Support external configuration, and applications can be flexibly configured through configuration files, environment variables, etc.

3. The underlying principle of Spring Boot

3.1 Automatic configuration principle

Spring Boot's automatic configuration mechanism is one of its core features. It passes@EnableAutoConfigurationAnnotation implementation automatically configures appropriate Spring components according to dependencies in the classpath. The implementation of automatic configuration mainly depends onSpringFactoriesLoaderClass and@EnableAutoConfigurationannotation.

When Spring Boot starts,SpringFactoriesLoaderWill scan the classpathMETA-INF/file, load the automatic configuration class defined in it. Each automatic configuration class will decide whether it takes effect based on certain conditions (such as whether there is a specific class or bean in the classpath).

3.2 File parsing source code API mechanism

Files are a key component of Spring Boot's automatic configuration mechanism. It is located under the classpathMETA-INFIn the directory, the automatic configuration classes and other extension points used to define Spring Boot.

3.2.1 File structure

A file is a simple attribute file with the following structure:

=\

Each line defines the interface name of an extension point and the corresponding implementation class name, and multiple implementation classes are separated by commas.

3.2.2 The parsing mechanism of SpringFactoriesLoader class

SpringFactoriesLoaderClass is Spring Boot for loadingThe tool class for the class defined in the file. The main methodloadFactoriesAll implementation classes used to load the specified interface:

public static <T> List<T> loadFactories(Class<T> factoryClass, ClassLoader classLoader) {
String factoryClassName = ();
try {
        Enumeration<URL> urls = (classLoader != null ? ("META-INF/") :
                ("META-INF/"));
        List<String> factoryNames = new ArrayList<>();
while (()) {
URL url = ();
Properties properties = (new UrlResource(url));
String factoryNamesProperty = (factoryClassName);
for (String factoryName : (factoryNamesProperty)) {
                (());
            }
        }
return instantiateFactories(factoryClass, factoryNames, classLoader);
    }
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
"META-INF/"]", ex);
    }
}

The method first passesMethods to find allMETA-INF/The URL of the file, then load the contents of these files one by one, parse out all implementation class names of the specified interface, and finally create instances of these classes through reflection and return.

3.3 Implementation principle of embedded server

Spring Boot has built-in servers such as Tomcat, Jetty or Undertow, allowing applications to run directly on these servers without external containers. The implementation principle of embedded server mainly includes the following steps:

  • Select a server: Choose which embedded server to use according to the project's dependency and configuration. For example, if the project containsspring-boot-starter-webDepend on, the Tomcat server is used by default.
  • Configure the server: Set the server's port number, context path, Session timeout and other attributes through configuration files or Java configuration classes.
  • Start the server: Create and start the embedded server when the application starts. Spring Boot byEmbeddedServletContainerFactoryInterfaces and implementation classes to manage the creation and startup process of embedded servers.

4. Handwriting simulation of Spring Boot startup process

In order to understand the startup process of Spring Boot more deeply, we can simulate the startup process of Spring Boot through Java code handwriting. Here is a simple simulation implementation:

4.1 Defining annotations and configuration classes

First, we define a custom annotation@ZhouyuSpringBootApplication, used to identify the startup class of Spring Boot application:

import ;
@SpringBootApplication
public @interface ZhouyuSpringBootApplication {
}

Then, we define a configuration classWebConfig, for configuring Spring MVC and view resolver:

import ;
import ;
import ;
import ;
import ;
import ;
import ;
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "")
public class WebConfig implements WebMvcConfigurer {
@Bean
public ViewResolver viewResolver() {
InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
        ("/WEB-INF/views/");
        (".jsp");
return viewResolver;
    }
}

4.2 Create SpringApplication class

Next, we create a custom oneSpringApplicationClass, used to start Spring Boot application:

import ;
import ;
import ;
public class ZhouyuSpringApplication {
public static void run(Class<?> primarySource, String... args) {
ConfigurableApplicationContext context = (primarySource, args);
        ();
    }
}

4.3 Create a startup class

Finally, we create a startup classMyAppand use@ZhouyuSpringBootApplicationAnnotation for annotation:

import ;
import ;
@ZhouyuSpringBootApplication
public class MyApp {
public static void main(String[] args) {
        (, args);
    }
}

4.4 Analysis of simulation files

For simulationThe file parsing process, we can create a tool classSpringFactoriesLoader, used to load all implementation classes of the specified interface:

import ;
import ;
import ;
import ;
import ;
import ;
public class SpringFactoriesLoader {
public static <T> List<T> loadFactories(Class<T> factoryClass, ClassLoader classLoader) throws IOException {
String factoryClassName = ();
        List<String> factoryNames = new ArrayList<>();
        Enumeration<URL> urls = ("META-INF/");
while (()) {
URL url = ();
try (InputStream is = ()) {
Properties properties = new Properties();
                (is);
String factoryNamesProperty = (factoryClassName);
for (String factoryName : (",")) {
                    (());
                }
            }
        }
        List<T> factories = new ArrayList<>();
for (String factoryName : factoryNames) {
try {
                Class<?> factoryClass = (factoryName, true, classLoader);
T factory = (T) ().newInstance();
                (factory);
            } catch (Exception e) {
throw new IllegalArgumentException("Unable to instantiate factory class: " + factoryName, e);
            }
        }
return factories;
    }
}

We can then use this tool class in the startup class to load and register the autoconfiguration class:

import ;
import ;
import ;
import ;
@ZhouyuSpringBootApplication
public class MyApp {
public static void main(String[] args) throws IOException {
        List&lt;ConfigurationClassPostProcessor&gt; postProcessors = (
                , ());
// Register automatic configuration classfor (ConfigurationClassPostProcessor postProcessor : postProcessors) {
// Here you can add logic to register the automatic configuration class        }
        (, args);
    }
}

It should be noted that the above code is just a simple simulation implementation and does not completely cover all the details of Spring Boot's startup process and automatic configuration mechanism. In practical applications, the startup process and automatic configuration mechanism of Spring Boot are much more complex, involving the collaborative work of multiple components and classes.

V. Conclusion

This article provides readers with a deeper understanding of Spring Boot by exploring the background history, business scenarios, functional points and underlying principles of Spring Boot. At the same time, the Spring Boot startup process is simulated by handwriting, especiallyThe source code API mechanism of file parsing enables readers to understand Spring Boot's automatic configuration mechanism more intuitively. I hope this article can provide useful reference and help for readers to better use Spring Boot in practical applications.

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