BAEL-2878 Guide to Spring's ApplicationContextRunner

spring-boot-autoconfiguration/src/main/java/com/baeldung/autoconfiguration/service/CustomService.java

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+package com.baeldung.autoconfiguration.service;
+
+public class CustomService implements SimpleService {
+
+    @Override
+    public String serve() {
+        return "Custom Service";
+    }
+
+}

spring-boot-autoconfiguration/src/main/java/com/baeldung/autoconfiguration/service/DefaultService.java

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+package com.baeldung.autoconfiguration.service;
+
+public class DefaultService implements SimpleService {
+
+    @Override
+    public String serve() {
+        return "Default Service";
+    }
+
+}

spring-boot-autoconfiguration/src/main/java/com/baeldung/autoconfiguration/service/SimpleService.java

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+package com.baeldung.autoconfiguration.service;
+
+public interface SimpleService {
+
+    public String serve();
+
+}

spring-boot-autoconfiguration/src/test/java/com/baeldung/autoconfiguration/ConditionalOnBeanTest.java

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+package com.baeldung.autoconfiguration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+public class ConditionalOnBeanTest {
+
+    private final ApplicationContextRunner contextRunner = new ApplicationContextRunner();
+
+    @Test
+    public void whenDependentBeanIsPresent_thenConditionalBeanCreated() {
+        this.contextRunner.withUserConfiguration(basicConfiguration.class, ConditionalOnBeanConfiguration.class)
+            .run((context) -> {
+                assertThat(context).hasBean("created");
+                assertThat(context).getBean("created")
+                    .isEqualTo("This is always created");
+                assertThat(context).hasBean("createOnBean");
+                assertThat(context).getBean("createOnBean")
+                    .isEqualTo("This is created when bean (name=created) is present");
+            });
+    }
+
+    @Test
+    public void whenDependentBeanIsPresent_thenConditionalMissingBeanIgnored() {
+        this.contextRunner.withUserConfiguration(basicConfiguration.class, ConditionalOnMissingBeanConfiguration.class)
+            .run((context) -> {
+                assertThat(context).hasBean("created");
+                assertThat(context).getBean("created")
+                    .isEqualTo("This is always created");
+                assertThat(context).doesNotHaveBean("createOnMissingBean");
+            });
+    }
+
+    @Test
+    public void whenDependentBeanIsNotPresent_thenConditionalMissingBeanCreated() {
+        this.contextRunner.withUserConfiguration(ConditionalOnMissingBeanConfiguration.class)
+            .run((context) -> {
+                assertThat(context).hasBean("createOnMissingBean");
+                assertThat(context).getBean("createOnMissingBean")
+                    .isEqualTo("This is created when bean (name=created) is missing");
+                assertThat(context).doesNotHaveBean("created");
+            });
+    }
+
+    @Configuration
+    protected static class basicConfiguration {
+        @Bean
+        public String created() {
+            return "This is always created";
+        }
+    }
+
+    @Configuration
+    @ConditionalOnBean(name = "created")
+    protected static class ConditionalOnBeanConfiguration {
+        @Bean
+        public String createOnBean() {
+            return "This is created when bean (name=created) is present";
+        }
+    }
+
+    @Configuration
+    @ConditionalOnMissingBean(name = "created")
+    protected static class ConditionalOnMissingBeanConfiguration {
+        @Bean
+        public String createOnMissingBean() {
+            return "This is created when bean (name=created) is missing";
+        }
+    }
+
+}

spring-boot-autoconfiguration/src/test/java/com/baeldung/autoconfiguration/ConditionalOnClassTest.java

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+package com.baeldung.autoconfiguration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingClass;
+import org.springframework.boot.test.context.FilteredClassLoader;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+public class ConditionalOnClassTest {
+
+    private final ApplicationContextRunner contextRunner = new ApplicationContextRunner();
+
+    @Test
+    public void whenDependentClassIsPresent_thenBeanCreated() {
+        this.contextRunner.withUserConfiguration(ConditionalOnClassConfiguration.class)
+            .run(context -> {
+                assertThat(context).hasBean("created");
+                assertThat(context.getBean("created")).isEqualTo("This is created when ConditionalOnClassTest is present on the classpath");
+            });
+    }
+
+    @Test
+    public void whenDependentClassIsPresent_thenBeanMissing() {
+        this.contextRunner.withUserConfiguration(ConditionalOnMissingClassConfiguration.class)
+            .run(context -> {
+                assertThat(context).doesNotHaveBean("missed");
+            });
+    }
+
+    @Test
+    public void whenDependentClassIsNotPresent_thenBeanMissing() {
+        this.contextRunner.withUserConfiguration(ConditionalOnClassConfiguration.class)
+            .withClassLoader(new FilteredClassLoader(ConditionalOnClassTest.class))
+            .run((context) -> {
+                assertThat(context).doesNotHaveBean("created");
+                assertThat(context).doesNotHaveBean(ConditionalOnClassTest.class);
+
+            });
+    }
+
+    @Test
+    public void whenDependentClassIsNotPresent_thenBeanCreated() {
+        this.contextRunner.withUserConfiguration(ConditionalOnMissingClassConfiguration.class)
+            .withClassLoader(new FilteredClassLoader(ConditionalOnClassTest.class))
+            .run((context) -> {
+                assertThat(context).hasBean("missed");
+                assertThat(context).getBean("missed")
+                    .isEqualTo("This is missed when ConditionalOnClassTest is present on the classpath");
+                assertThat(context).doesNotHaveBean(ConditionalOnClassTest.class);
+
+            });
+    }
+
+    @Configuration
+    @ConditionalOnClass(ConditionalOnClassTest.class)
+    protected static class ConditionalOnClassConfiguration {
+        @Bean
+        public String created() {
+            return "This is created when ConditionalOnClassTest is present on the classpath";
+        }
+    }
+
+    @Configuration
+    @ConditionalOnMissingClass("com.baeldung.autoconfiguration.ConditionalOnClassTest")
+    protected static class ConditionalOnMissingClassConfiguration {
+        @Bean
+        public String missed() {
+            return "This is missed when ConditionalOnClassTest is present on the classpath";
+        }
+    }
+
+}

spring-boot-autoconfiguration/src/test/java/com/baeldung/autoconfiguration/ConditionalOnPropertyTest.java

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+package com.baeldung.autoconfiguration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.test.context.TestPropertySource;
+
+import com.baeldung.autoconfiguration.service.CustomService;
+import com.baeldung.autoconfiguration.service.DefaultService;
+import com.baeldung.autoconfiguration.service.SimpleService;
+
+public class ConditionalOnPropertyTest {
+
+    private final ApplicationContextRunner contextRunner = new ApplicationContextRunner();
+
+    @Test
+    public void whenGivenCustomPropertyValue_thenCustomServiceCreated() {
+        this.contextRunner.withPropertyValues("com.baeldung.service=custom")
+            .withUserConfiguration(SimpleServiceConfiguration.class)
+            .run(context -> {
+                assertThat(context).hasBean("customService");
+                SimpleService simpleService = context.getBean(CustomService.class);
+                assertThat(simpleService.serve()).isEqualTo("Custom Service");
+                assertThat(context).doesNotHaveBean("defaultService");
+            });
+    }
+
+    @Test
+    public void whenGivenDefaultPropertyValue_thenDefaultServiceCreated() {
+        this.contextRunner.withPropertyValues("com.baeldung.service=default")
+            .withUserConfiguration(SimpleServiceConfiguration.class)
+            .run(context -> {
+                assertThat(context).hasBean("defaultService");
+                SimpleService simpleService = context.getBean(DefaultService.class);
+                assertThat(simpleService.serve()).isEqualTo("Default Service");
+                assertThat(context).doesNotHaveBean("customService");
+            });
+    }
+
+    @Configuration
+    @TestPropertySource("classpath:ConditionalOnPropertyTest.properties")
+    protected static class SimpleServiceConfiguration {
+
+        @Bean
+        @ConditionalOnProperty(name = "com.baeldung.service", havingValue = "default")
+        @ConditionalOnMissingBean
+        public DefaultService defaultService() {
+            return new DefaultService();
+        }
+
+        @Bean
+        @ConditionalOnProperty(name = "com.baeldung.service", havingValue = "custom")
+        @ConditionalOnMissingBean
+        public CustomService customService() {
+            return new CustomService();
+        }
+    }
+
+}

spring-boot-autoconfiguration/src/test/resources/ConditionalOnPropertyTest.properties

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+com.baeldung.service=custom