BAEL-1217 Guide to Spring Type Conversions

spring-boot/.gitignore

@@ -2,4 +2,3 @@
 .settings/
 .classpath
 .project
-/.apt_generated/

spring-boot/src/main/java/org/baeldung/config/WebConfig.java

@@ -1,7 +1,11 @@
 package org.baeldung.config;
 
+import org.baeldung.converter.GenericBigDecimalConverter;
+import org.baeldung.converter.StringToEnumConverterFactory;
+import org.baeldung.converter.StringToEmployeeConverter;
 import org.baeldung.web.resolver.HeaderVersionArgumentResolver;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.format.FormatterRegistry;
 import org.springframework.web.method.support.HandlerMethodArgumentResolver;
 import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
 
@@ -14,4 +18,11 @@ public class WebConfig extends WebMvcConfigurerAdapter {
     public void addArgumentResolvers(final List<HandlerMethodArgumentResolver> argumentResolvers) {
         argumentResolvers.add(new HeaderVersionArgumentResolver());
     }
+
+    @Override
+    public void addFormatters(FormatterRegistry registry) {
+        registry.addConverter(new StringToEmployeeConverter());
+        registry.addConverterFactory(new StringToEnumConverterFactory());
+        registry.addConverter(new GenericBigDecimalConverter());
+    }
 }

spring-boot/src/main/java/org/baeldung/converter/GenericBigDecimalConverter.java

@@ -0,0 +1,36 @@
+package org.baeldung.converter;
+
+import com.google.common.collect.ImmutableSet;
+import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.convert.converter.GenericConverter;
+
+import java.math.BigDecimal;
+import java.util.Set;
+
+public class GenericBigDecimalConverter implements GenericConverter {
+    @Override
+    public Set<ConvertiblePair> getConvertibleTypes () {
+
+        ConvertiblePair[] pairs = new ConvertiblePair[] {
+                new ConvertiblePair(Number.class, BigDecimal.class),
+                new ConvertiblePair(String.class, BigDecimal.class)};
+
+        return ImmutableSet.copyOf(pairs);
+    }
+
+    @Override
+    public Object convert (Object source, TypeDescriptor sourceType,
+                           TypeDescriptor targetType) {
+        if (sourceType.getType() == BigDecimal.class) {
+            return source;
+        }
+
+        if(sourceType.getType() == String.class) {
+            String number = (String) source;
+            return new BigDecimal(number);
+        } else {
+            Number number = (Number) source;
+            return new BigDecimal(number.doubleValue());
+        }
+    }
+}

spring-boot/src/main/java/org/baeldung/converter/StringToEmployeeConverter.java

@@ -0,0 +1,14 @@
+package org.baeldung.converter;
+
+
+import com.baeldung.toggle.Employee;
+import org.springframework.core.convert.converter.Converter;
+
+public class StringToEmployeeConverter implements Converter<String, Employee> {
+
+    @Override
+    public Employee convert(String from) {
+        String[] data = from.split(",");
+        return new Employee(Long.parseLong(data[0]), Double.parseDouble(data[1]));
+    }
+}

spring-boot/src/test/java/org/baeldung/converter/CustomConverterTest.java

@@ -0,0 +1,45 @@
+package org.baeldung.converter;
+
+import com.baeldung.toggle.Employee;
+import org.baeldung.Application;
+import org.baeldung.domain.Modes;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.core.convert.ConversionService;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.test.context.web.WebAppConfiguration;
+
+import java.math.BigDecimal;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringBootTest(classes = Application.class)
+@WebAppConfiguration
+public class CustomConverterTest {
+
+    @Autowired
+    ConversionService conversionService;
+
+    @Test
+    public void whenConvertStringToIntegerUsingDefaultConverter_thenSuccess() {
+        System.out.println(conversionService.convert("25", Integer.class));
+    }
+
+    @Test
+    public void whenConvertStringToEmployee_thenSuccess() {
+        System.out.println(conversionService.convert("1,50000.00", Employee.class));
+    }
+
+    @Test
+    public void whenConvertStringToEnum_thenSuccess() {
+        System.out.println(conversionService.convert("ALPHA", Modes.class));
+    }
+
+    @Test
+    public void whenConvertingToBigDecimalUsingGenericConverter_thenSuccess() {
+        System.out.println(conversionService.convert(Integer.valueOf(11), BigDecimal.class));
+        System.out.println(conversionService.convert(Double.valueOf(25.23), BigDecimal.class));
+        System.out.println(conversionService.convert("2.32", BigDecimal.class));
+    }
+}