Add Liquibase rollback file support

Add a `liquibase.rollback-file` property which can be used to write
a rollback file when migrations occur.

Fixes gh-1826
Closes gh-5535

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/liquibase/LiquibaseAutoConfiguration.java

@@ -105,6 +105,7 @@ public class LiquibaseAutoConfiguration {
 			liquibase.setShouldRun(this.properties.isEnabled());
 			liquibase.setLabels(this.properties.getLabels());
 			liquibase.setChangeLogParameters(this.properties.getParameters());
+			liquibase.setRollbackFile(this.properties.getRollbackFile());
 			return liquibase;
 		}
 

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/liquibase/LiquibaseProperties.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.liquibase;
 
+import java.io.File;
 import java.util.Map;
 
 import javax.validation.constraints.NotNull;
@@ -90,6 +91,11 @@ public class LiquibaseProperties {
 	 */
 	private Map<String, String> parameters;
 
+	/**
+	 * The file to which rollback SQL will be written when an update is performed.
+	 */
+	private File rollbackFile;
+
 	public String getChangeLog() {
 		return this.changeLog;
 	}
@@ -178,4 +184,12 @@ public class LiquibaseProperties {
 		this.parameters = parameters;
 	}
 
+	public File getRollbackFile() {
+		return this.rollbackFile;
+	}
+
+	public void setRollbackFile(File rollbackFile) {
+		this.rollbackFile = rollbackFile;
+	}
+
 }

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/liquibase/LiquibaseAutoConfigurationTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.liquibase;
 
+import java.io.File;
 import java.util.Map;
 
 import liquibase.integration.spring.SpringLiquibase;
@@ -24,6 +25,7 @@ import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
+import org.junit.rules.TemporaryFolder;
 
 import org.springframework.beans.factory.BeanCreationException;
 import org.springframework.boot.autoconfigure.PropertyPlaceholderAutoConfiguration;
@@ -32,6 +34,7 @@ import org.springframework.boot.liquibase.CommonsLoggingLiquibaseLogger;
 import org.springframework.boot.test.util.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.test.util.ReflectionTestUtils;
+import org.springframework.util.FileCopyUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -45,6 +48,9 @@ public class LiquibaseAutoConfigurationTests {
 	@Rule
 	public ExpectedException expected = ExpectedException.none();
 
+	@Rule
+	public TemporaryFolder temp = new TemporaryFolder();
+
 	private AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
 
 	@Before
@@ -192,4 +198,20 @@ public class LiquibaseAutoConfigurationTests {
 		assertThat(parameters.get("foo")).isEqualTo("bar");
 	}
 
+	@Test
+	public void testRollbackFile() throws Exception {
+		File file = this.temp.newFile("rollback-file.sql");
+		EnvironmentTestUtils.addEnvironment(this.context,
+				"liquibase.rollbackFile:" + file.getAbsolutePath());
+		this.context.register(EmbeddedDataSourceConfiguration.class,
+				LiquibaseAutoConfiguration.class,
+				PropertyPlaceholderAutoConfiguration.class);
+		this.context.refresh();
+		SpringLiquibase liquibase = this.context.getBean(SpringLiquibase.class);
+		File actualFile = (File) ReflectionTestUtils.getField(liquibase, "rollbackFile");
+		assertThat(actualFile).isEqualTo(file).exists();
+		String content = new String(FileCopyUtils.copyToByteArray(file));
+		assertThat(content).contains("DROP TABLE PUBLIC.customer;");
+	}
+
 }