add valueswithdefaults example (#2369)

* add values with defaults example

* add additional examples

* remove unused imports

spring-core/src/main/java/com/baeldung/valuewithdefaults/ValuesWithDefaultsApp.java

@@ -0,0 +1,75 @@
+package com.baeldung.valuewithdefaults;
+
+import java.util.Arrays;
+import java.util.List;
+
+import javax.annotation.PostConstruct;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.PropertySource;
+import org.springframework.util.Assert;
+
+import com.google.common.collect.Lists;
+import com.google.common.primitives.Ints;
+
+/**
+ * Demonstrates setting defaults for @Value annotation.  Note that there are no properties 
+ * defined in the specified property source.  We also assume that the user here
+ * does not have a system property named some.key.
+ *
+ */
+@Configuration
+@PropertySource(name = "myProperties", value = "valueswithdefaults.properties")
+public class ValuesWithDefaultsApp {
+
+    @Value("${some.key:my default value}")
+    private String stringWithDefaultValue;
+
+    @Value("${some.key:}")
+    private String stringWithBlankDefaultValue;
+
+    @Value("${some.key:true}")
+    private boolean booleanWithDefaultValue;
+    
+    @Value("${some.key:42}")
+    private int intWithDefaultValue;  
+
+    @Value("${some.key:one,two,three}")
+    private String[] stringArrayWithDefaults;
+
+    @Value("${some.key:1,2,3}")
+    private int[] intArrayWithDefaults;
+
+    @Value("#{systemProperties['some.key'] ?: 'my default system property value'}")
+    private String spelWithDefaultValue;
+    
+
+    public static void main(String[] args) {
+        ApplicationContext applicationContext = new AnnotationConfigApplicationContext(ValuesWithDefaultsApp.class);
+    }
+
+    @PostConstruct
+    public void afterInitialize() {
+    	// strings
+    	Assert.isTrue(stringWithDefaultValue.equals("my default value"));
+    	Assert.isTrue(stringWithBlankDefaultValue.equals(""));
+    	
+    	// other primitives
+    	Assert.isTrue(booleanWithDefaultValue);
+    	Assert.isTrue(intWithDefaultValue == 42);
+    	
+    	// arrays
+    	List<String> stringListValues = Lists.newArrayList("one", "two", "three");
+    	Assert.isTrue(Arrays.asList(stringArrayWithDefaults).containsAll(stringListValues));
+
+    	List<Integer> intListValues = Lists.newArrayList(1, 2, 3);
+    	Assert.isTrue(Ints.asList(intArrayWithDefaults).containsAll(intListValues));
+
+    	// SpEL
+    	Assert.isTrue(spelWithDefaultValue.equals("my default system property value"));
+    	
+    }
+}