add default value

src/main/java/org/jilt/Builder.java

@@ -333,4 +333,11 @@
     @Retention(RetentionPolicy.SOURCE)
     @interface Ignore {
     }
+
+    @Target(ElementType.FIELD)
+    @Retention(RetentionPolicy.SOURCE)
+    @interface Default {
+
+        String value();
+    }
 }

src/main/java/org/jilt/internal/AbstractBuilderGenerator.java

@@ -88,12 +88,14 @@ public final void generateBuilderClass() throws Exception {
         for (VariableElement attribute : attributes) {
             String fieldName = attributeSimpleName(attribute);
             TypeName fieldType = TypeName.get(attribute.asType());
+            Builder.Default defaultAnnot = attribute.getAnnotation(Builder.Default.class);
 
             builderClassBuilder.addField(FieldSpec
                     .builder(fieldType, fieldName,
                             this.builderClassNeedsToBeAbstract()
                                 ? Modifier.PROTECTED
                                 : Modifier.PRIVATE)
+                            .initializer(defaultAnnot != null ? defaultAnnot.value() : "")
                     .build());
 
             MethodSpec setterMethod = this.generateBuilderSetterMethod(attribute);

src/test/java/org/jilt/test/DefaultTest.java

@@ -0,0 +1,28 @@
+package org.jilt.test;
+
+import org.jilt.test.data.defaultvalue.DefaultValue;
+import org.jilt.test.data.defaultvalue.DefaultValueBuilder;
+import org.junit.Test;
+
+import java.util.Collections;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DefaultTest {
+
+    @Test
+    public void set_attribute_to_default_value_when_is_not_specified_in_builder(){
+        DefaultValue value = DefaultValueBuilder
+                .defaultValue()
+                .attr4(12)
+                .build();
+
+
+        assertThat(value.attr1).isEqualTo(1);
+        assertThat(value.attr2).isEqualTo("attr2");
+        assertThat(value.attr3).isTrue();
+        assertThat(value.attr4).isEqualTo(12);
+        assertThat(value.attrs).isEqualTo(Collections.emptySet());
+    }
+
+}

src/test/java/org/jilt/test/data/defaultvalue/DefaultValue.java

@@ -0,0 +1,32 @@
+package org.jilt.test.data.defaultvalue;
+
+import org.jilt.Builder;
+
+import java.util.Set;
+
+@Builder
+public class DefaultValue {
+
+    @Builder.Default("1")
+    public int attr1;
+
+    @Builder.Default("\"attr2\"")
+    public String attr2;
+
+    @Builder.Default("true")
+    public boolean attr3;
+
+    @Builder.Default("1000")
+    public int attr4;
+
+    @Builder.Default("java.util.Collections.emptySet()")
+    public Set<String> attrs;
+
+    public DefaultValue(int attr1, String attr2, boolean attr3, int attr4, Set<String> attrs) {
+        this.attr1 = attr1;
+        this.attr2 = attr2;
+        this.attr3 = attr3;
+        this.attr4 = attr4;
+        this.attrs = attrs;
+    }
+}