Ignore binding failures for env vars and system properties

1.3.0.M4 tightened up the configuration property binding such that
ignoreUnknownFields = false now works as intended. Unfortunately, this
has led to some complaints as applications that worked with 1.2.x have
stopped working. For example, a SERVER_HOME environment variable does
not cause a failure in 1.2.x despite there being no home property on
ServerProperties but will now fail in 1.3.0.M4.

This commit updates RelaxedDataBinder to ignore binding failures for
properties that come from a source outside of the application’s control,
namely environment variables and system properties.

Closes gh-3775

spring-boot/src/main/java/org/springframework/boot/bind/RelaxedDataBinder.java

@@ -18,6 +18,7 @@ package org.springframework.boot.bind;
 
 import java.net.InetAddress;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
@@ -35,6 +36,7 @@ import org.springframework.beans.MutablePropertyValues;
 import org.springframework.beans.NotWritablePropertyException;
 import org.springframework.beans.PropertyValue;
 import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.env.StandardEnvironment;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 import org.springframework.util.StringUtils;
@@ -54,6 +56,11 @@ import org.springframework.validation.DataBinder;
  */
 public class RelaxedDataBinder extends DataBinder {
 
+	private static final Set<String> BENIGN_PROPERTY_SOURCE_NAMES = Collections
+			.unmodifiableSet(new HashSet<String>(Arrays.asList(
+					StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,
+					StandardEnvironment.SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME)));
+
 	private static final Object BLANK = new Object();
 
 	private String namePrefix;
@@ -254,13 +261,21 @@ public class RelaxedDataBinder extends DataBinder {
 						}
 						catch (NotWritablePropertyException ex) {
 							PropertyOrigin origin = findPropertyOrigin(pv);
+							if (isFatal(origin)) {
 								if (origin != null) {
-								throw new RelaxedBindingNotWritablePropertyException(ex,
-										origin);
+									throw new RelaxedBindingNotWritablePropertyException(
+											ex, origin);
 								}
+								else {
 									throw ex;
 								}
 							}
+							else {
+								logger.debug("Ignoring benign property binding failure",
+										ex);
+							}
+						}
+					}
 				};
 				beanWrapper.setConversionService(new RelaxedConversionService(
 						getConversionService()));
@@ -271,6 +286,13 @@ public class RelaxedDataBinder extends DataBinder {
 		};
 	}
 
+	private boolean isFatal(PropertyOrigin origin) {
+		if (origin == null) {
+			return true;
+		}
+		return !BENIGN_PROPERTY_SOURCE_NAMES.contains(origin.getSource().getName());
+	}
+
 	private PropertyOrigin findPropertyOrigin(PropertyValue propertyValue) {
 		if (propertyValue instanceof OriginCapablePropertyValue) {
 			return ((OriginCapablePropertyValue) propertyValue).getOrigin();

spring-boot/src/test/java/org/springframework/boot/bind/PropertiesConfigurationFactoryTests.java

@@ -24,8 +24,11 @@ import javax.validation.constraints.NotNull;
 import org.junit.Test;
 import org.springframework.beans.NotWritablePropertyException;
 import org.springframework.context.support.StaticMessageSource;
+import org.springframework.core.env.MutablePropertySources;
+import org.springframework.core.env.StandardEnvironment;
 import org.springframework.core.io.ByteArrayResource;
 import org.springframework.core.io.support.PropertiesLoaderUtils;
+import org.springframework.mock.env.MockPropertySource;
 import org.springframework.validation.BindException;
 import org.springframework.validation.Validator;
 import org.springframework.validation.beanvalidation.SpringValidatorAdapter;
@@ -82,6 +85,37 @@ public class PropertiesConfigurationFactoryTests {
 		bindFoo("bar: blah");
 	}
 
+	@Test
+	public void systemEnvironmentBindingFailuresAreIgnored() throws Exception {
+		setupFactory();
+		MutablePropertySources propertySources = new MutablePropertySources();
+		MockPropertySource propertySource = new MockPropertySource(
+				StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME);
+		propertySource.setProperty("doesNotExist", "foo");
+		propertySource.setProperty("name", "bar");
+		propertySources.addFirst(propertySource);
+		this.factory.setPropertySources(propertySources);
+		this.factory.setIgnoreUnknownFields(false);
+		this.factory.afterPropertiesSet();
+		this.factory.getObject();
+		Foo foo = this.factory.getObject();
+		assertEquals("bar", foo.name);
+	}
+
+	@Test
+	public void systemPropertyBindingFailuresAreIgnored() throws Exception {
+		setupFactory();
+		MutablePropertySources propertySources = new MutablePropertySources();
+		MockPropertySource propertySource = new MockPropertySource(
+				StandardEnvironment.SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME);
+		propertySource.setProperty("doesNotExist", "foo");
+		propertySource.setProperty("name", "bar");
+		propertySources.addFirst(propertySource);
+		this.factory.setPropertySources(propertySources);
+		this.factory.setIgnoreUnknownFields(false);
+		this.factory.afterPropertiesSet();
+	}
+
 	private Foo createFoo(final String values) throws Exception {
 		setupFactory();
 		return bindFoo(values);