Polish contribution

Closes gh-5521

spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc

@@ -1351,11 +1351,14 @@ for use within Logback. This can be useful if you want to access values from you
 `application.properties` file in your logback configuration. The tag works in a similar
 way to Logback's standard `<property>` tag, but rather than specifying a direct `value`
 you specify the `source` of the property (from the `Environment`). You can use the `scope`
-attribute if you need to store the property somewhere other than in `local` scope.
+attribute if you need to store the property somewhere other than in `local` scope. If
+you need a fallback value in case the property is not set in the `Environment`, you can
+use the `defaultValue` attribute.
 
 [source,xml,indent=0]
 ----
-	<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"/>
+	<springProperty scope="context" name="fluentHost" source="myapp.fluentd.host"
+			defaultValue="localhost"/>
 	<appender name="FLUENT" class="ch.qos.logback.more.appenders.DataFluentAppender">
 		<remoteHost>${fluentHost}</remoteHost>
 		...

spring-boot/src/main/java/org/springframework/boot/logging/logback/SpringPropertyAction.java

@@ -62,9 +62,6 @@ class SpringPropertyAction extends Action {
 	private String getValue(String source, String defaultValue) {
 		if (this.environment == null) {
 			addWarn("No Spring Environment available to resolve " + source);
-			return null;
-		}
-		if (source == null) {
 			return defaultValue;
 		}
 		String value = this.environment.getProperty(source);
@@ -76,9 +73,9 @@ class SpringPropertyAction extends Action {
 			String prefix = source.substring(0, lastDot + 1);
 			RelaxedPropertyResolver resolver = new RelaxedPropertyResolver(
 					this.environment, prefix);
-			return resolver.getProperty(source.substring(lastDot + 1));
+			return resolver.getProperty(source.substring(lastDot + 1), defaultValue);
 		}
-		return null;
+		return defaultValue;
 	}
 
 	@Override

spring-boot/src/test/java/org/springframework/boot/logging/logback/SpringBootJoranConfiguratorTests.java

@@ -41,6 +41,7 @@ import static org.hamcrest.Matchers.not;
  *
  * @author Phillip Webb
  * @author Eddú Meléndez
+ * @author Stephane Nicoll
  */
 public class SpringBootJoranConfiguratorTests {
 
@@ -140,10 +141,28 @@ public class SpringBootJoranConfiguratorTests {
 		assertThat(this.context.getProperty("MINE")).isEqualTo("test");
 	}
 
+	@Test
+	public void springPropertyNoValue() throws Exception {
+		initialize("property.xml");
+		assertThat(this.context.getProperty("SIMPLE")).isNull();
+	}
+
+	@Test
+	public void relaxedSpringPropertyNoValue() throws Exception {
+		initialize("property.xml");
+		assertThat(this.context.getProperty("MINE")).isNull();
+	}
+
 	@Test
 	public void springPropertyWithDefaultValue() throws Exception {
-		initialize("property-defaultValue.xml");
-		assertThat(this.context.getProperty("MINE")).isEqualTo("foo");
+		initialize("property-default-value.xml");
+		assertThat(this.context.getProperty("SIMPLE")).isEqualTo("foo");
+	}
+
+	@Test
+	public void relaxedSpringPropertyWithDefaultValue() throws Exception {
+		initialize("property-default-value.xml");
+		assertThat(this.context.getProperty("MINE")).isEqualTo("bar");
 	}
 
 	private void doTestNestedProfile(boolean expected, String... profiles)

spring-boot/src/test/resources/org/springframework/boot/logging/logback/property-defaultValue.xml → spring-boot/src/test/resources/org/springframework/boot/logging/logback/property-default-value.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <configuration>
 	<include resource="org/springframework/boot/logging/logback/base.xml" />
-	<springProperty scope="context" name="MINE" defaultValue="foo"/>
+	<springProperty scope="context" name="SIMPLE" source="testpropertyfoobar" defaultValue="foo"/>
+	<springProperty scope="context" name="MINE" source="my.example-property" defaultValue="bar"/>
 </configuration>

spring-boot/src/test/resources/org/springframework/boot/logging/logback/property.xml

 <?xml version="1.0" encoding="UTF-8"?>
 <configuration>
 	<include resource="org/springframework/boot/logging/logback/base.xml" />
+	<springProperty scope="context" name="SIMPLE" source="testpropertyfoobar"/>
 	<springProperty scope="context" name="MINE" source="my.example-property"/>
 </configuration>