Unlock Spring Boot Internals: 8 Essential Tools to Inspect Your Application

Environment: SpringBoot 3.2.5

1. Get Process ID

Use ApplicationPid to obtain the current process ID.

ApplicationPid pid = new ApplicationPid();
System.out.printf("Process ID: %s%n", pid.toString());

Output example: Process ID: 24416 Alternative methods:

# Register listener in META-INF/spring.factories
org.springframework.context.ApplicationListener=\
org.springframework.boot.context.ApplicationPidFileWriter

Configure the file path:

spring:
  pid:
    file: d:/app.pid

File content (example):

Another way using the JMX bean:

String pid = ManagementFactory.getRuntimeMXBean().getName().split("@")[0];

2. Application Home Directory

ApplicationHome provides the main directory of the application, handling JAR files, exploded archives, or directly run programs.

ApplicationHome home = new ApplicationHome();
System.out.printf("dir: %s, source: %s%n", home.getDir(), home.getSource());

IDE run output: dir: D:\java\workspace\test-app, source: null JAR run output:

dir: D:\java\workspace\test-app\target,
source: D:\java\workspace\test-app\target\test-app-1.0.0.jar

3. Get Java Version

Use JavaVersion to retrieve the Java version at runtime.

System.out.printf("Java Version: %s%n", JavaVersion.getJavaVersion());

Output example: Java Version: 17 JavaVersion is an enum covering versions 17‑22; you can compare versions with isEqualOrNewerThan and isOlderThan.

4. Application Temporary Directory

ApplicationTemp gives access to a dedicated temporary directory for the Spring Boot application.

ApplicationTemp temp = new ApplicationTemp();
System.out.printf("Temp directory: %s%n", temp.getDir());

Output example:

Temp directory: C:\Users\MSI-NB\AppData\Local\Temp\561929B2C764E67BCDA2DF9DAE26EF121F7E5365

5. System Properties / Environment Variables

Use SystemProperties to read system properties; if a property is missing, it falls back to environment variables.

System.out.printf("java.home=%s%n", SystemProperties.get("java.home"));

Output example: java.home=D:\software\jre The get method accepts var‑args keys and returns the first non‑null value.

6. Instantiator – Bulk Bean Creation

Instantiator is a simple factory that creates multiple instances of a given type using supplied class names.

public interface DAO {}
public class A implements DAO {}
public class B implements DAO {}

Instantiator<DAO> instant = new Instantiator<>(DAO.class, p -> {});
List<DAO> ret = instant.instantiate(List.of("com.pack.A", "com.pack.B"));
System.out.printf("%s%n", ret);

Output example:

[com.pack.A@3127cb44, com.pack.B@3234474]

7. Resource Loading

Load .properties, .xml, or .yaml resources using PropertiesPropertySourceLoader and YamlPropertySourceLoader .

// Load properties file
PropertiesPropertySourceLoader propertyLoader = new PropertiesPropertySourceLoader();
List<PropertySource<?>> list = propertyLoader.load("pack", new ClassPathResource("pack.properties"));
System.out.printf("pack.*: %s%n", list.get(0).getSource());

// Load yaml file
YamlPropertySourceLoader yamlLoader = new YamlPropertySourceLoader();
List<PropertySource<?>> yamls = yamlLoader.load("pack", new ClassPathResource("pack.yml"));
System.out.printf("pack.*: %s%n", yamls.get(0).getSource());

The loaded PropertySource objects can be registered with the Environment for direct access.

8. Get Base Packages

Retrieve the base packages of the current application context using AutoConfigurationPackages .

private ConfigurableApplicationContext context;
System.out.printf("basePackages: %s%n", AutoConfigurationPackages.get(context));

Output example: basePackages: [com.pack] The underlying bean is private, so this static helper is the only way to access it.