背景
在分层的代码架构中，层与层之间的对象避免不了要做很多转换、赋值等操作，这些操作重复且繁琐，于是乎催生出很多工具来优雅，高效地完成这个操作，有BeanUtils、BeanCopier、Dozer、Orika等等，本文将讲述上面几个工具的使用、性能对比及原理分析。
性能分析
其实这几个工具要做的事情很简单，而且在使用上也是类似的，所以我觉得先给大家看看性能分析的对比结果，让大家有一个大概的认识。我是使用JMH来做性能分析的，代码如下：
要复制的对象比较简单，包含了一些基本类型；有一次warmup，因为一些工具是需要“预编译”和做缓存的，这样做对比才会比较客观；分别复制1000、10000、100000个对象，这是比较常用数量级了吧。
@BenchmarkMode(Mode.AverageTime) @OutputTimeUnit(TimeUnit.MICROSECONDS) @Fork(1) @Warmup(iterations = 1) @State(Scope.Benchmark) public class BeanMapperBenchmark { @Param({"1000", "10000", "100000"}) private int times; private int time; private static MapperFactory mapperFactory; private static Mapper mapper; static { mapperFactory = new DefaultMapperFactory.Builder().build(); mapperFactory.classMap(SourceVO.class, TargetVO.class) .byDefault() .register(); mapper = DozerBeanMapperBuilder.create() .withMappingBuilder(new BeanMappingBuilder() { @Override protected void configure() { mapping(SourceVO.class, TargetVO.class) .fields("fullName", "name") .exclude("in"); } }).build(); } public static void main(String[] args) throws Exception { Options options = new OptionsBuilder() .include(BeanMapperBenchmark.class.getName()).measurementIterations(3) .build(); new Runner(options).run(); } @Setup public void prepare() { this.time = times; } @Benchmark public void springBeanUtilTest(){ SourceVO sourceVO = getSourceVO(); for(int i = 0; i < time; i++){ TargetVO targetVO = new TargetVO(); BeanUtils.copyProperties(sourceVO, targetVO); } } @Benchmark public void apacheBeanUtilTest() throws Exception{ SourceVO sourceVO = getSourceVO(); for(int i = 0; i < time; i++){ TargetVO targetVO = new TargetVO(); org.apache.commons.beanutils.BeanUtils.copyProperties(targetVO, sourceVO); } } @Benchmark public void beanCopierTest(){ SourceVO sourceVO = getSourceVO(); for(int i = 0; i < time; i++){ TargetVO targetVO = new TargetVO(); BeanCopier bc = BeanCopier.create(SourceVO.class, TargetVO.class, false); bc.copy(sourceVO, targetVO, null); } } @Benchmark public void dozerTest(){ SourceVO sourceVO = getSourceVO(); for(int i = 0; i < time; i++){ TargetVO map = mapper.map(sourceVO, TargetVO.class); } } @Benchmark public void orikaTest(){ SourceVO sourceVO = getSourceVO(); for(int i = 0; i < time; i++){ MapperFacade mapper = mapperFactory.getMapperFacade(); TargetVO map = mapper.map(sourceVO, TargetVO.class); } } private SourceVO getSourceVO(){ SourceVO sourceVO = new SourceVO(); sourceVO.setP1(1); sourceVO.setP2(2L); sourceVO.setP3(new Integer(3).byteValue()); sourceVO.setDate1(new Date()); sourceVO.setPattr1("1"); sourceVO.setIn(new SourceVO.Inner(1)); sourceVO.setFullName("alben"); return sourceVO; } }
在我macbook下运行后的结果如下：
图片
Score表示的是平均运行时间，单位是微秒。从执行效率来看，可以看出 beanCopier > orika > springBeanUtil > dozer > apacheBeanUtil。这样的结果跟它们各自的实现原理有很大的关系，
下面将详细每个工具的使用及实现原理。
Spring的BeanUtils
使用
这个工具可能是大家日常使用最多的，因为是Spring自带的，使用也简单：BeanUtils.copyProperties(sourceVO, targetVO);
原理
Spring BeanUtils的实现原理也比较简答，就是通过Java的Introspector获取到两个类的PropertyDescriptor，对比两个属性具有相同的名字和类型，如果是，则进行赋值（通过ReadMethod获取值，通过WriteMethod赋值），否则忽略。
为了提高性能Spring对BeanInfo和PropertyDescriptor进行了缓存。
（源码基于：org.springframework:spring-beans:4.3.9.RELEASE）
/** * Copy the property values of the given source bean into the given target bean. * <p>Note: The source and target classes do not have to match or even be derived * from each other, as long as the properties match. Any bean properties that the * source bean exposes but the target bean does not will silently be ignored. * @param source the source bean * @param target the target bean * @param editable the class (or interface) to restrict property setting to * @param ignoreProperties array of property names to ignore * @throws BeansException if the copying failed * @see BeanWrapper */ private static void copyProperties(Object source, Object target, Class<?> editable, String... ignoreProperties) throws BeansException { Assert.notNull(source, "Source must not be null"); Assert.notNull(target, "Target must not be null"); Class<?> actualEditable = target.getClass(); if (editable != null) { if (!editable.isInstance(target)) { throw new IllegalArgumentException("Target class [" + target.getClass().getName() + "] not assignable to Editable class [" + editable.getName() + "]"); } actualEditable = editable; } //获取target类的属性（有缓存） PropertyDescriptor[] targetPds = getPropertyDescriptors(actualEditable); List<String> ignoreList = (ignoreProperties != null ? Arrays.asList(ignoreProperties) : null); for (PropertyDescriptor targetPd : targetPds) { Method writeMethod = targetPd.getWriteMethod(); if (writeMethod != null && (ignoreList == null || !ignoreList.contains(targetPd.getName()))) { //获取source类的属性（有缓存） PropertyDescriptor sourcePd = getPropertyDescriptor(source.getClass(), targetPd.getName()); if (sourcePd != null) { Method readMethod = sourcePd.getReadMethod(); if (readMethod != null && //判断target的setter方法入参和source的getter方法返回类型是否一致 ClassUtils.isAssignable(writeMethod.getParameterTypes()[0], readMethod.getReturnType())) { try { if (!Modifier.isPublic(readMethod.getDeclaringClass().getModifiers())) { readMethod.setAccessible(true); } //获取源值 Object value = readMethod.invoke(source); if (!Modifier.isPublic(writeMethod.getDeclaringClass().getModifiers())) { writeMethod.setAccessible(true); } //赋值到target writeMethod.invoke(target, value); } catch (Throwable ex) { throw new FatalBeanException( "Could not copy property '" + targetPd.getName() + "' from source to target", ex); } } } } } }
小结
Spring BeanUtils的实现就是这么简洁，这也是它性能比较高的原因。
不过，过于简洁就失去了灵活性和可扩展性了，Spring BeanUtils的使用限制也比较明显，要求类属性的名字和类型一致，这点在使用时要注意。
Apache的BeanUtils
使用
Apache的BeanUtils和Spring的BeanUtils的使用是一样的：
BeanUtils.copyProperties(targetVO, sourceVO);
要注意，source和target的入参位置不同。
原理
Apache的BeanUtils的实现原理跟Spring的BeanUtils一样，也是主要通过Java的Introspector机制获取到类的属性来进行赋值操作，对BeanInfo和PropertyDescriptor同样有缓存，但是Apache BeanUtils加了一些不那么使用的特性（包括支持Map类型、支持自定义的DynaBean类型、支持属性名的表达式等等）在里面，使得性能相对Spring的BeanUtils来说有所下降。
（源码基于：commons-beanutils:commons-beanutils:1.9.3）
public void copyProperties(final Object dest, final Object orig) throws IllegalAccessException, InvocationTargetException { if (dest == null) { throw new IllegalArgumentException ("No destination bean specified"); } if (orig == null) { throw new IllegalArgumentException("No origin bean specified"); } if (log.isDebugEnabled()) { log.debug("BeanUtils.copyProperties(" + dest + ", " + orig + ")"); } // Apache Common自定义的DynaBean if (orig instanceof DynaBean) { final DynaProperty[] origDescriptors = ((DynaBean) orig).getDynaClass().getDynaProperties(); for (DynaProperty origDescriptor : origDescriptors) { final String name = origDescriptor.getName(); // Need to check isReadable() for WrapDynaBean // (see Jira issue# BEANUTILS-61) if (getPropertyUtils().isReadable(orig, name) && getPropertyUtils().isWriteable(dest, name)) { final Object value = ((DynaBean) orig).get(name); copyProperty(dest, name, value); } } // Map类型 } else if (orig instanceof Map) { @SuppressWarnings("unchecked") final // Map properties are always of type <String, Object> Map<String, Object> propMap = (Map<String, Object>) orig; for (final Map.Entry<String, Object> entry : propMap.entrySet()) { final String name = entry.getKey(); if (getPropertyUtils().isWriteable(dest, name)) { copyProperty(dest, name, entry.getValue()); } } // 标准的JavaBean } else { final PropertyDescriptor[] origDescriptors = //获取PropertyDescriptor getPropertyUtils().getPropertyDescriptors(orig); for (PropertyDescriptor origDescriptor : origDescriptors) { final String name = origDescriptor.getName(); if ("class".equals(name)) { continue; // No point in trying to set an object's class } //是否可读和可写 if (getPropertyUtils().isReadable(orig, name) && getPropertyUtils().isWriteable(dest, name)) { try { //获取源值 final Object value = getPropertyUtils().getSimpleProperty(orig, name); //赋值操作 copyProperty(dest, name, value); } catch (final NoSuchMethodException e) { // Should not happen } } } } }
小结
Apache BeanUtils的实现跟Spring BeanUtils总体上类似，但是性能却低很多，这个可以从上面性能比较看出来。阿里的Java规范是不建议使用的。
BeanCopier
使用
BeanCopier在cglib包里，它的使用也比较简单：
@Test public void beanCopierSimpleTest() { SourceVO sourceVO = getSourceVO(); log.info("source={}", GsonUtil.toJson(sourceVO)); TargetVO targetVO = new TargetVO(); BeanCopier bc = BeanCopier.create(SourceVO.class, TargetVO.class, false); bc.copy(sourceVO, targetVO, null); log.info("target={}", GsonUtil.toJson(targetVO)); }
只需要预先定义好要转换的source类和target类就好了，可以选择是否使用Converter，这个下面会说到。
在上面的性能测试中，BeanCopier是所有中表现最好的，那么我们分析一下它的实现原理。
原理
BeanCopier的实现原理跟BeanUtils截然不同，它不是利用反射对属性进行赋值，而是直接使用cglib来生成带有的get/set方法的class类，然后执行。由于是直接生成字节码执行，所以BeanCopier的性能接近手写
get/set。
BeanCopier.create方法
public static BeanCopier create(Class source, Class target, boolean useConverter) { Generator gen = new Generator(); gen.setSource(source); gen.setTarget(target); gen.setUseConverter(useConverter); return gen.create(); } public BeanCopier create() { Object key = KEY_FACTORY.newInstance(source.getName(), target.getName(), useConverter); return (BeanCopier)super.create(key); }
这里的意思是用KEY_FACTORY创建一个BeanCopier出来，然后调用create方法来生成字节码。
KEY_FACTORY其实就是用cglib通过BeanCopierKey接口生成出来的一个类
private static final BeanCopierKey KEY_FACTORY = (BeanCopierKey)KeyFactory.create(BeanCopierKey.class); interface BeanCopierKey { public Object newInstance(String source, String target, boolean useConverter); }
通过设置
System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY, "path");
可以让cglib输出生成类的class文件，我们可以反编译看看里面的代码
下面是KEY_FACTORY的类
public class BeanCopier$BeanCopierKey$$KeyFactoryByCGLIB$$f32401fd extends KeyFactory implements BeanCopierKey { private final String FIELD_0; private final String FIELD_1; private final boolean FIELD_2; public BeanCopier$BeanCopierKey$$KeyFactoryByCGLIB$$f32401fd() { } public Object newInstance(String var1, String var2, boolean var3) { return new BeanCopier$BeanCopierKey$$KeyFactoryByCGLIB$$f32401fd(var1, var2, var3); } public BeanCopier$BeanCopierKey$$KeyFactoryByCGLIB$$f32401fd(String var1, String var2, boolean var3) { this.FIELD_0 = var1; this.FIELD_1 = var2; this.FIELD_2 = var3; } //省去hashCode等方法。。。 }
继续跟踪Generator.create方法，由于Generator是继承AbstractClassGenerator，这个AbstractClassGenerator是cglib用来生成字节码的一个模板类，Generator的super.create其实调用
AbstractClassGenerator的create方法，最终会调用到Generator的模板方法generateClass方法，我们不去细究AbstractClassGenerator的细节，重点看generateClass。
这个是一个生成java类的方法，理解起来就好像我们平时写代码一样。
public void generateClass(ClassVisitor v) { Type sourceType = Type.getType(source); Type targetType = Type.getType(target); ClassEmitter ce = new ClassEmitter(v); //开始“写”类，这里有修饰符、类名、父类等信息 ce.begin_class(Constants.V1_2, Constants.ACC_PUBLIC, getClassName(), BEAN_COPIER, null, Constants.SOURCE_FILE); //没有构造方法 EmitUtils.null_constructor(ce); //开始“写”一个方法，方法名是copy CodeEmitter e = ce.begin_method(Constants.ACC_PUBLIC, COPY, null); //通过Introspector获取source类和target类的PropertyDescriptor PropertyDescriptor[] getters = ReflectUtils.getBeanGetters(source); PropertyDescriptor[] setters = ReflectUtils.getBeanSetters(target); Map names = new HashMap(); for (int i = 0; i < getters.length; i++) { names.put(getters[i].getName(), getters[i]); } Local targetLocal = e.make_local(); Local sourceLocal = e.make_local(); if (useConverter) { e.load_arg(1); e.checkcast(targetType); e.store_local(targetLocal); e.load_arg(0); e.checkcast(sourceType); e.store_local(sourceLocal); } else { e.load_arg(1); e.checkcast(targetType); e.load_arg(0); e.checkcast(sourceType); } //通过属性名来生成转换的代码 //以setter作为遍历 for (int i = 0; i < setters.length; i++) { PropertyDescriptor setter = setters[i]; //根据setter的name获取getter PropertyDescriptor getter = (PropertyDescriptor)names.get(setter.getName()); if (getter != null) { //获取读写方法 MethodInfo read = ReflectUtils.getMethodInfo(getter.getReadMethod()); MethodInfo write = ReflectUtils.getMethodInfo(setter.getWriteMethod()); //如果用了useConverter，则进行下面的拼装代码方式 if (useConverter) { Type setterType = write.getSignature().getArgumentTypes()[0]; e.load_local(targetLocal); e.load_arg(2); e.load_local(sourceLocal); e.invoke(read); e.box(read.getSignature().getReturnType()); EmitUtils.load_class(e, setterType); e.push(write.getSignature().getName()); e.invoke_interface(CONVERTER, CONVERT); e.unbox_or_zero(setterType); e.invoke(write); //compatible用来判断getter和setter是否类型一致 } else if (compatible(getter, setter)) { e.dup2(); e.invoke(read); e.invoke(write); } } } e.return_value(); e.end_method(); ce.end_class(); } private static boolean compatible(PropertyDescriptor getter, PropertyDescriptor setter) { // TODO: allow automatic widening conversions? return setter.getPropertyType().isAssignableFrom(getter.getPropertyType()); }
即使没有使用过cglib也能读懂生成代码的流程吧，我们看看没有使用useConverter的情况下生成的代码：
public class Object$$BeanCopierByCGLIB$$d1d970c8 extends BeanCopier { public Object$$BeanCopierByCGLIB$$d1d970c8() { } public void copy(Object var1, Object var2, Converter var3) { TargetVO var10000 = (TargetVO)var2; SourceVO var10001 = (SourceVO)var1; var10000.setDate1(((SourceVO)var1).getDate1()); var10000.setIn(var10001.getIn()); var10000.setListData(var10001.getListData()); var10000.setMapData(var10001.getMapData()); var10000.setP1(var10001.getP1()); var10000.setP2(var10001.getP2()); var10000.setP3(var10001.getP3()); var10000.setPattr1(var10001.getPattr1()); } }
在对比上面生成代码的代码是不是阔然开朗了。
再看看使用useConverter的情况：
public class Object$$BeanCopierByCGLIB$$d1d970c7 extends BeanCopier { private static final Class CGLIB$load_class$java$2Eutil$2EDate; private static final Class CGLIB$load_class$beanmapper_compare$2Evo$2ESourceVO$24Inner; private static final Class CGLIB$load_class$java$2Eutil$2EList; private static final Class CGLIB$load_class$java$2Eutil$2EMap; private static final Class CGLIB$load_class$java$2Elang$2EInteger; private static final Class CGLIB$load_class$java$2Elang$2ELong; private static final Class CGLIB$load_class$java$2Elang$2EByte; private static final Class CGLIB$load_class$java$2Elang$2EString; public Object$$BeanCopierByCGLIB$$d1d970c7() { } public void copy(Object var1, Object var2, Converter var3) { TargetVO var4 = (TargetVO)var2; SourceVO var5 = (SourceVO)var1; var4.setDate1((Date)var3.convert(var5.getDate1(), CGLIB$load_class$java$2Eutil$2EDate, "setDate1")); var4.setIn((Inner)var3.convert(var5.getIn(), CGLIB$load_class$beanmapper_compare$2Evo$2ESourceVO$24Inner, "setIn")); var4.setListData((List)var3.convert(var5.getListData(), CGLIB$load_class$java$2Eutil$2EList, "setListData")); var4.setMapData((Map)var3.convert(var5.getMapData(), CGLIB$load_class$java$2Eutil$2EMap, "setMapData")); var4.setP1((Integer)var3.convert(var5.getP1(), CGLIB$load_class$java$2Elang$2EInteger, "setP1")); var4.setP2((Long)var3.convert(var5.getP2(), CGLIB$load_class$java$2Elang$2ELong, "setP2")); var4.setP3((Byte)var3.convert(var5.getP3(), CGLIB$load_class$java$2Elang$2EByte, "setP3")); var4.setPattr1((String)var3.convert(var5.getPattr1(), CGLIB$load_class$java$2Elang$2EString, "setPattr1")); var4.setSeq((Long)var3.convert(var5.getSeq(), CGLIB$load_class$java$2Elang$2ELong, "setSeq")); } static void CGLIB$STATICHOOK1() { CGLIB$load_class$java$2Eutil$2EDate = Class.forName("java.util.Date"); CGLIB$load_class$beanmapper_compare$2Evo$2ESourceVO$24Inner = Class.forName("beanmapper_compare.vo.SourceVO$Inner"); CGLIB$load_class$java$2Eutil$2EList = Class.forName("java.util.List"); CGLIB$load_class$java$2Eutil$2EMap = Class.forName("java.util.Map"); CGLIB$load_class$java$2Elang$2EInteger = Class.forName("java.lang.Integer"); CGLIB$load_class$java$2Elang$2ELong = Class.forName("java.lang.Long"); CGLIB$load_class$java$2Elang$2EByte = Class.forName("java.lang.Byte"); CGLIB$load_class$java$2Elang$2EString = Class.forName("java.lang.String"); } static { CGLIB$STATICHOOK1(); } }
小结
BeanCopier性能确实很高，但从源码可以看出BeanCopier只会拷贝名称和类型都相同的属性，而且如果一旦使用Converter，BeanCopier只使用Converter定义的规则去拷贝属性，所以在convert方法中要考虑所有的属性。
Dozer
使用
上面提到的BeanUtils和BeanCopier都是功能比较简单的，需要属性名称一样，甚至类型也要一样。但是在大多数情况下这个要求就相对苛刻了，要知道有些VO由于各种原因不能修改，有些是外部接口SDK的对象，
有些对象的命名规则不同，例如有驼峰型的，有下划线的等等，各种什么情况都有。所以我们更加需要的是更加灵活丰富的功能，甚至可以做到定制化的转换。
Dozer就提供了这些功能，有支持同名隐式映射，支持基本类型互相转换，支持显示指定映射关系，支持exclude字段，支持递归匹配映射，支持深度匹配，支持Date to String的date-formate，支持自定义转换Converter，支持一次mapping定义多处使用，支持EventListener事件监听等等。不仅如此，Dozer在使用方式上，除了支持API，还支持XML和注解，满足大家的喜好。更多的功能可以参考这里
由于其功能很丰富，不可能每个都演示，这里只是给个大概认识，更详细的功能，或者XML和注解的配置，请看官方文档。
private Mapper dozerMapper; @Before public void setup(){ dozerMapper = DozerBeanMapperBuilder.create() .withMappingBuilder(new BeanMappingBuilder() { @Override protected void configure() { mapping(SourceVO.class, TargetVO.class) .fields("fullName", "name") .exclude("in"); } }) .withCustomConverter(null) .withEventListener(null) .build(); } @Test public void dozerTest(){ SourceVO sourceVO = getSourceVO(); log.info("sourceVO={}", GsonUtil.toJson(sourceVO)); TargetVO map = dozerMapper.map(sourceVO, TargetVO.class); log.info("map={}", GsonUtil.toJson(map)); }
原理
Dozer的实现原理本质上还是用反射/Introspector那套，但是其丰富的功能，以及支持多种实现方式（API、XML、注解）使得代码看上去有点复杂，在翻阅代码时，我们大可不必理会这些类，只需要知道它们大体的作用就行了，重点关注核心流程和代码的实现。下面我们重点看看构建mapper的build方法和实现映射的map方法。
build方法很简单，它是一个初始化的动作，就是通过用户的配置来构建出一系列后面要用到的配置对象、上下文对象，或其他封装对象，我们不必深究这些对象是怎么实现的，从名字上我们大概能猜出这些对象是干嘛，负责什么就可以了。
DozerBeanMapper(List<String> mappingFiles, BeanContainer beanContainer, DestBeanCreator destBeanCreator, DestBeanBuilderCreator destBeanBuilderCreator, BeanMappingGenerator beanMappingGenerator, PropertyDescriptorFactory propertyDescriptorFactory, List<CustomConverter> customConverters, List<MappingFileData> mappingsFileData, List<EventListener> eventListeners, CustomFieldMapper customFieldMapper, Map<String, CustomConverter> customConvertersWithId, ClassMappings customMappings, Configuration globalConfiguration, CacheManager cacheManager) { this.beanContainer = beanContainer; this.destBeanCreator = destBeanCreator; this.destBeanBuilderCreator = destBeanBuilderCreator; this.beanMappingGenerator = beanMappingGenerator; this.propertyDescriptorFactory = propertyDescriptorFactory; this.customConverters = new ArrayList<>(customConverters); this.eventListeners = new ArrayList<>(eventListeners); this.mappingFiles = new ArrayList<>(mappingFiles); this.customFieldMapper = customFieldMapper; this.customConvertersWithId = new HashMap<>(customConvertersWithId); this.eventManager = new DefaultEventManager(eventListeners); this.customMappings = customMappings; this.globalConfiguration = globalConfiguration; this.cacheManager = cacheManager; }
map方法是映射对象的过程，其入口是MappingProcessor的mapGeneral方法
private <T> T mapGeneral(Object srcObj, final Class<T> destClass, final T destObj, final String mapId) { srcObj = MappingUtils.deProxy(srcObj, beanContainer); Class<T> destType; T result; if (destClass == null) { destType = (Class<T>)destObj.getClass(); result = destObj; } else { destType = destClass; result = null; } ClassMap classMap = null; try { //构建ClassMap //ClassMap是包括src类和dest类和其他配置的一个封装 classMap = getClassMap(srcObj.getClass(), destType, mapId); //注册事件 eventManager.on(new DefaultEvent(EventTypes.MAPPING_STARTED, classMap, null, srcObj, result, null)); //看看有没有自定义converter Class<?> converterClass = MappingUtils.findCustomConverter(converterByDestTypeCache, classMap.getCustomConverters(), srcObj .getClass(), destType); if (destObj == null) { // If this is a nested MapperAware conversion this mapping can be already processed // but we can do this optimization only in case of no destObject, instead we must copy to the dest object Object alreadyMappedValue = mappedFields.getMappedValue(srcObj, destType, mapId); if (alreadyMappedValue != null) { return (T)alreadyMappedValue; } } //优先使用自定义converter进行映射 if (converterClass != null) { return (T)mapUsingCustomConverter(converterClass, srcObj.getClass(), srcObj, destType, result, null, true); } //也是对配置进行了封装 BeanCreationDirective creationDirective = new BeanCreationDirective(srcObj, classMap.getSrcClassToMap(), classMap.getDestClassToMap(), destType, classMap.getDestClassBeanFactory(), classMap.getDestClassBeanFactoryId(), classMap.getDestClassCreateMethod(), classMap.getDestClass().isSkipConstructor()); //继续进行映射 result = createByCreationDirectiveAndMap(creationDirective, classMap, srcObj, result, false, null); } catch (Throwable e) { MappingUtils.throwMappingException(e); } eventManager.on(new DefaultEvent(EventTypes.MAPPING_FINISHED, classMap, null, srcObj, result, null)); return result; }
一般情况下createByCreationDirectiveAndMap方法会一直调用到mapFromFieldMap方法，而在没有自定义converter的情况下会调用mapOrRecurseObject方法
大多数情况下字段的映射会在这个方法做一般的解析
private Object mapOrRecurseObject(Object srcObj, Object srcFieldValue, Class<?> destFieldType, FieldMap fieldMap, Object destObj) { Class<?> srcFieldClass = srcFieldValue != null ? srcFieldValue.getClass() : fieldMap.getSrcFieldType(srcObj.getClass()); Class<?> converterClass = MappingUtils.determineCustomConverter(fieldMap, converterByDestTypeCache, fieldMap.getClassMap() .getCustomConverters(), srcFieldClass, destFieldType); //自定义converter的处理 if (converterClass != null) { return mapUsingCustomConverter(converterClass, srcFieldClass, srcFieldValue, destFieldType, destObj, fieldMap, false); } if (srcFieldValue == null) { return null; } String srcFieldName = fieldMap.getSrcFieldName(); String destFieldName = fieldMap.getDestFieldName(); if (!(DozerConstants.SELF_KEYWORD.equals(srcFieldName) && DozerConstants.SELF_KEYWORD.equals(destFieldName))) { Object alreadyMappedValue = mappedFields.getMappedValue(srcFieldValue, destFieldType, fieldMap.getMapId()); if (alreadyMappedValue != null) { return alreadyMappedValue; } } //如果只是浅拷贝则直接返回（可配置） if (fieldMap.isCopyByReference()) { // just get the src and return it, no transformation. return srcFieldValue; } //对Map类型的处理 boolean isSrcFieldClassSupportedMap = MappingUtils.isSupportedMap(srcFieldClass); boolean isDestFieldTypeSupportedMap = MappingUtils.isSupportedMap(destFieldType); if (isSrcFieldClassSupportedMap && isDestFieldTypeSupportedMap) { return mapMap(srcObj, (Map<?, ?>)srcFieldValue, fieldMap, destObj); } if (fieldMap instanceof MapFieldMap && destFieldType.equals(Object.class)) { destFieldType = fieldMap.getDestHintContainer() != null ? fieldMap.getDestHintContainer().getHint() : srcFieldClass; } //对基本类型的映射处理 //PrimitiveOrWrapperConverter类支持兼容了基本类型之间的互相转换 if (primitiveConverter.accepts(srcFieldClass) || primitiveConverter.accepts(destFieldType)) { // Primitive or Wrapper conversion if (fieldMap.getDestHintContainer() != null) { Class<?> destHintType = fieldMap.getDestHintType(srcFieldValue.getClass()); // if the destType is null this means that there was more than one hint. // we must have already set the destType then. if (destHintType != null) { destFieldType = destHintType; } } //#1841448 - if trim-strings=true, then use a trimmed src string value when converting to dest value Object convertSrcFieldValue = srcFieldValue; if (fieldMap.isTrimStrings() && srcFieldValue.getClass().equals(String.class)) { convertSrcFieldValue = ((String)srcFieldValue).trim(); } DateFormatContainer dfContainer = new DateFormatContainer(fieldMap.getDateFormat()); if (fieldMap instanceof MapFieldMap && !primitiveConverter.accepts(destFieldType)) { return primitiveConverter.convert(convertSrcFieldValue, convertSrcFieldValue.getClass(), dfContainer); } else { return primitiveConverter.convert(convertSrcFieldValue, destFieldType, dfContainer, destFieldName, destObj); } } //对集合类型的映射处理 if (MappingUtils.isSupportedCollection(srcFieldClass) && (MappingUtils.isSupportedCollection(destFieldType))) { return mapCollection(srcObj, srcFieldValue, fieldMap, destObj); } //对枚举类型的映射处理 if (MappingUtils.isEnumType(srcFieldClass, destFieldType)) { return mapEnum((Enum)srcFieldValue, (Class<Enum>)destFieldType); } if (fieldMap.getDestDeepIndexHintContainer() != null) { destFieldType = fieldMap.getDestDeepIndexHintContainer().getHint(); } //其他复杂对象类型的处理 return mapCustomObject(fieldMap, destObj, destFieldType, destFieldName, srcFieldValue); }
mapCustomObject方法。其实你会发现这个方法最重要的一点就是做递归处理，无论是最后调用createByCreationDirectiveAndMap还是mapToDestObject方法。
private Object mapCustomObject(FieldMap fieldMap, Object destObj, Class<?> destFieldType, String destFieldName, Object srcFieldValue) { srcFieldValue = MappingUtils.deProxy(srcFieldValue, beanContainer); // Custom java bean. Need to make sure that the destination object is not // already instantiated. Object result = null; // in case of iterate feature new objects are created in any case if (!DozerConstants.ITERATE.equals(fieldMap.getDestFieldType())) { result = getExistingValue(fieldMap, destObj, destFieldType); } // if the field is not null than we don't want a new instance if (result == null) { // first check to see if this plain old field map has hints to the actual // type. if (fieldMap.getDestHintContainer() != null) { Class<?> destHintType = fieldMap.getDestHintType(srcFieldValue.getClass()); // if the destType is null this means that there was more than one hint. // we must have already set the destType then. if (destHintType != null) { destFieldType = destHintType; } } // Check to see if explicit map-id has been specified for the field // mapping String mapId = fieldMap.getMapId(); Class<?> targetClass; if (fieldMap.getDestHintContainer() != null && fieldMap.getDestHintContainer().getHint() != null) { targetClass = fieldMap.getDestHintContainer().getHint(); } else { targetClass = destFieldType; } ClassMap classMap = getClassMap(srcFieldValue.getClass(), targetClass, mapId); BeanCreationDirective creationDirective = new BeanCreationDirective(srcFieldValue, classMap.getSrcClassToMap(), classMap.getDestClassToMap(), destFieldType, classMap.getDestClassBeanFactory(), classMap.getDestClassBeanFactoryId(), fieldMap.getDestFieldCreateMethod() != null ? fieldMap.getDestFieldCreateMethod() : classMap.getDestClassCreateMethod(), classMap.getDestClass().isSkipConstructor(), destObj, destFieldName); result = createByCreationDirectiveAndMap(creationDirective, classMap, srcFieldValue, null, false, fieldMap.getMapId()); } else { mapToDestObject(null, srcFieldValue, result, false, fieldMap.getMapId()); } return result; }
小结
Dozer功能强大，但底层还是用反射那套，所以在性能测试中它的表现一般，仅次于Apache的BeanUtils。如果不追求性能的话，可以使用。
Orika
Orika可以说是几乎集成了上述几个工具的优点，不仅具有丰富的功能，底层使用Javassist生成字节码，运行 效率很高的。
使用
Orika基本支持了Dozer支持的功能，这里我也是简单介绍一下Orika的使用，具体更详细的API可以参考User Guide。
private MapperFactory mapperFactory; @Before public void setup() { mapperFactory = new DefaultMapperFactory.Builder().build(); ConverterFactory converterFactory = mapperFactory.getConverterFactory(); converterFactory.registerConverter(new TypeConverter()); mapperFactory.classMap(SourceVO.class, TargetVO.class) .field("fullName", "name") .field("type", "enumType") .exclude("in") .byDefault() .register(); } @Test public void main() { MapperFacade mapper = mapperFactory.getMapperFacade(); SourceVO sourceVO = getSourceVO(); log.info("sourceVO={}", GsonUtil.toJson(sourceVO)); TargetVO map = mapper.map(sourceVO, TargetVO.class); log.info("map={}", GsonUtil.toJson(map)); }
原理
在讲解实现原理时，我们先看看Orika在背后干了什么事情。
通过增加以下配置，我们可以看到Orika在做映射过程中生成mapper的源码和字节码。
System.setProperty("ma.glasnost.orika.writeSourceFiles", "true"); System.setProperty("ma.glasnost.orika.writeClassFiles", "true"); System.setProperty("ma.glasnost.orika.writeSourceFilesToPath", "path"); System.setProperty("ma.glasnost.orika.writeClassFilesToPath", "path");
用上面的例子，我们看看Orika生成的java代码：
package ma.glasnost.orika.generated; public class Orika_TargetVO_SourceVO_Mapper947163525829122$0 extends ma.glasnost.orika.impl.GeneratedMapperBase { public void mapAtoB(java.lang.Object a, java.lang.Object b, ma.glasnost.orika.MappingContext mappingContext) { super.mapAtoB(a, b, mappingContext); // sourceType: SourceVO beanmapper_compare.vo.SourceVO source = ((beanmapper_compare.vo.SourceVO)a); // destinationType: TargetVO beanmapper_compare.vo.TargetVO destination = ((beanmapper_compare.vo.TargetVO)b); destination.setName(((java.lang.String)source.getFullName())); if ( !(((java.lang.Integer)source.getType()) == null)){ destination.setEnumType(((beanmapper_compare.vo.TargetVO.EnumType)((ma.glasnost.orika.Converter)usedConverters[0]).convert(((java.lang.Integer)source.getType()), ((ma.glasnost.orika.metadata.Type)usedTypes[0]), mappingContext))); } else { destination.setEnumType(null); } if ( !(((java.util.Date)source.getDate1()) == null)){ destination.setDate1(((java.util.Date)((ma.glasnost.orika.Converter)usedConverters[1]).convert(((java.util.Date)source.getDate1()), ((ma.glasnost.orika.metadata.Type)usedTypes[1]), mappingContext))); } else { destination.setDate1(null); }if ( !(((java.util.List)source.getListData()) == null)) { java.util.List new_listData = ((java.util.List)new java.util.ArrayList()); new_listData.addAll(mapperFacade.mapAsList(((java.util.List)source.getListData()), ((ma.glasnost.orika.metadata.Type)usedTypes[2]), ((ma.glasnost.orika.metadata.Type)usedTypes[3]), mappingContext)); destination.setListData(new_listData); } else { if ( !(((java.util.List)destination.getListData()) == null)) { destination.setListData(null); }; }if ( !(((java.util.Map)source.getMapData()) == null)){ java.util.Map new_mapData = ((java.util.Map)new java.util.LinkedHashMap()); for( java.util.Iterator mapData_$_iter = ((java.util.Map)source.getMapData()).entrySet().iterator(); mapData_$_iter.hasNext(); ) { java.util.Map.Entry sourceMapDataEntry = ((java.util.Map.Entry)mapData_$_iter.next()); java.lang.Integer newMapDataKey = null; java.util.List newMapDataVal = null; if ( !(((java.lang.Long)sourceMapDataEntry.getKey()) == null)){ newMapDataKey = ((java.lang.Integer)((ma.glasnost.orika.Converter)usedConverters[2]).convert(((java.lang.Long)sourceMapDataEntry.getKey()), ((ma.glasnost.orika.metadata.Type)usedTypes[3]), mappingContext)); } else { newMapDataKey = null; } if ( !(((java.util.List)sourceMapDataEntry.getValue()) == null)) { java.util.List new_newMapDataVal = ((java.util.List)new java.util.ArrayList()); new_newMapDataVal.addAll(mapperFacade.mapAsList(((java.util.List)sourceMapDataEntry.getValue()), ((ma.glasnost.orika.metadata.Type)usedTypes[2]), ((ma.glasnost.orika.metadata.Type)usedTypes[4]), mappingContext)); newMapDataVal = new_newMapDataVal; } else { if ( !(newMapDataVal == null)) { newMapDataVal = null; }; } new_mapData.put(newMapDataKey, newMapDataVal); } destination.setMapData(new_mapData); } else { destination.setMapData(null); } destination.setP1(((java.lang.Integer)source.getP1())); destination.setP2(((java.lang.Long)source.getP2())); destination.setP3(((java.lang.Byte)source.getP3())); destination.setPattr1(((java.lang.String)source.getPattr1())); if ( !(((java.lang.String)source.getSeq()) == null)){ destination.setSeq(((java.lang.Long)((ma.glasnost.orika.Converter)usedConverters[3]).convert(((java.lang.String)source.getSeq()), ((ma.glasnost.orika.metadata.Type)usedTypes[2]), mappingContext))); } else { destination.setSeq(null); } if(customMapper != null) { customMapper.mapAtoB(source, destination, mappingContext); } } public void mapBtoA(java.lang.Object a, java.lang.Object b, ma.glasnost.orika.MappingContext mappingContext) { super.mapBtoA(a, b, mappingContext); // sourceType: TargetVO beanmapper_compare.vo.TargetVO source = ((beanmapper_compare.vo.TargetVO)a); // destinationType: SourceVO beanmapper_compare.vo.SourceVO destination = ((beanmapper_compare.vo.SourceVO)b); destination.setFullName(((java.lang.String)source.getName())); if ( !(((beanmapper_compare.vo.TargetVO.EnumType)source.getEnumType()) == null)){ destination.setType(((java.lang.Integer)((ma.glasnost.orika.Converter)usedConverters[0]).convert(((beanmapper_compare.vo.TargetVO.EnumType)source.getEnumType()), ((ma.glasnost.orika.metadata.Type)usedTypes[3]), mappingContext))); } else { destination.setType(null); } if ( !(((java.util.Date)source.getDate1()) == null)){ destination.setDate1(((java.util.Date)((ma.glasnost.orika.Converter)usedConverters[1]).convert(((java.util.Date)source.getDate1()), ((ma.glasnost.orika.metadata.Type)usedTypes[1]), mappingContext))); } else { destination.setDate1(null); }if ( !(((java.util.List)source.getListData()) == null)) { java.util.List new_listData = ((java.util.List)new java.util.ArrayList()); new_listData.addAll(mapperFacade.mapAsList(((java.util.List)source.getListData()), ((ma.glasnost.orika.metadata.Type)usedTypes[3]), ((ma.glasnost.orika.metadata.Type)usedTypes[2]), mappingContext)); destination.setListData(new_listData); } else { if ( !(((java.util.List)destination.getListData()) == null)) { destination.setListData(null); }; }if ( !(((java.util.Map)source.getMapData()) == null)){ java.util.Map new_mapData = ((java.util.Map)new java.util.LinkedHashMap()); for( java.util.Iterator mapData_$_iter = ((java.util.Map)source.getMapData()).entrySet().iterator(); mapData_$_iter.hasNext(); ) { java.util.Map.Entry sourceMapDataEntry = ((java.util.Map.Entry)mapData_$_iter.next()); java.lang.Long newMapDataKey = null; java.util.List newMapDataVal = null; if ( !(((java.lang.Integer)sourceMapDataEntry.getKey()) == null)){ newMapDataKey = ((java.lang.Long)((ma.glasnost.orika.Converter)usedConverters[2]).convert(((java.lang.Integer)sourceMapDataEntry.getKey()), ((ma.glasnost.orika.metadata.Type)usedTypes[2]), mappingContext)); } else { newMapDataKey = null; } if ( !(((java.util.List)sourceMapDataEntry.getValue()) == null)) { java.util.List new_newMapDataVal = ((java.util.List)new java.util.ArrayList()); new_newMapDataVal.addAll(mapperFacade.mapAsList(((java.util.List)sourceMapDataEntry.getValue()), ((ma.glasnost.orika.metadata.Type)usedTypes[4]), ((ma.glasnost.orika.metadata.Type)usedTypes[2]), mappingContext)); newMapDataVal = new_newMapDataVal; } else { if ( !(newMapDataVal == null)) { newMapDataVal = null; }; } new_mapData.put(newMapDataKey, newMapDataVal); } destination.setMapData(new_mapData); } else { destination.setMapData(null); } destination.setP1(((java.lang.Integer)source.getP1())); destination.setP2(((java.lang.Long)source.getP2())); destination.setP3(((java.lang.Byte)source.getP3())); destination.setPattr1(((java.lang.String)source.getPattr1())); if ( !(((java.lang.Long)source.getSeq()) == null)){ destination.setSeq(((java.lang.String)((ma.glasnost.orika.Converter)usedConverters[4]).convert(((java.lang.Long)source.getSeq()), ((ma.glasnost.orika.metadata.Type)usedTypes[5]), mappingContext))); } else { destination.setSeq(null); } if(customMapper != null) { customMapper.mapBtoA(source, destination, mappingContext); } } }
这个mapper类就两个方法mapAtoB和mapBtoA，从名字看猜到前者是负责src -> dest的映射，后者是负责dest -> src的映射。
好，我们们看看实现的过程。
Orika的使用跟Dozer的类似，首先通过配置生成一个MapperFactory，再用MapperFacade来作为映射的统一入口，这里MapperFactory和MapperFacade都是单例的。mapperFactory在做配置类映射时，只是注册了ClassMap，还没有真正的生成mapper的字节码，是在第一次调用getMapperFacade方法时才初始化mapper。下面看看getMapperFacade。
（源码基于 ma.glasnost.orika:orika-core:1.5.4）
public MapperFacade getMapperFacade() { if (!isBuilt) { synchronized (mapperFacade) { if (!isBuilt) { build(); } } } return mapperFacade; }
利用注册的ClassMap信息和MappingContext上下文信息来构造mapper
public synchronized void build() { if (!isBuilding && !isBuilt) { isBuilding = true; MappingContext context = contextFactory.getContext(); try { if (useBuiltinConverters) { BuiltinConverters.register(converterFactory); } converterFactory.setMapperFacade(mapperFacade); for (Map.Entry<MapperKey, ClassMap<Object, Object>> classMapEntry : classMapRegistry.entrySet()) { ClassMap<Object, Object> classMap = classMapEntry.getValue(); if (classMap.getUsedMappers().isEmpty()) { classMapEntry.setValue(classMap.copyWithUsedMappers(discoverUsedMappers(classMap))); } } buildClassMapRegistry(); Map<ClassMap<?, ?>, GeneratedMapperBase> generatedMappers = new HashMap<ClassMap<?, ?>, GeneratedMapperBase>(); //重点看这里 //在使用mapperFactory配置classMap时，会存放在classMapRegistry里 for (ClassMap<?, ?> classMap : classMapRegistry.values()) { //对每个classMap生成一个mapper，重点看buildMapper方法 generatedMappers.put(classMap, buildMapper(classMap, false, context)); } Set<Entry<ClassMap<?, ?>, GeneratedMapperBase>> generatedMapperEntries = generatedMappers.entrySet(); for (Entry<ClassMap<?, ?>, GeneratedMapperBase> generatedMapperEntry : generatedMapperEntries) { buildObjectFactories(generatedMapperEntry.getKey(), context); initializeUsedMappers(generatedMapperEntry.getValue(), generatedMapperEntry.getKey(), context); } } finally { contextFactory.release(context); } isBuilt = true; isBuilding = false; } } public Set<ClassMap<Object, Object>> lookupUsedClassMap(MapperKey mapperKey) { Set<ClassMap<Object, Object>> usedClassMapSet = usedMapperMetadataRegistry.get(mapperKey); if (usedClassMapSet == null) { usedClassMapSet = Collections.emptySet(); } return usedClassMapSet; }
跟踪buildMapper方法
private GeneratedMapperBase buildMapper(ClassMap<?, ?> classMap, boolean isAutoGenerated, MappingContext context) { register(classMap.getAType(), classMap.getBType(), isAutoGenerated); register(classMap.getBType(), classMap.getAType(), isAutoGenerated); final MapperKey mapperKey = new MapperKey(classMap.getAType(), classMap.getBType()); //调用mapperGenerator的build方法生成mapper final GeneratedMapperBase mapper = mapperGenerator.build(classMap, context); mapper.setMapperFacade(mapperFacade); mapper.setFromAutoMapping(isAutoGenerated); if (classMap.getCustomizedMapper() != null) { final Mapper<Object, Object> customizedMapper = (Mapper<Object, Object>) classMap.getCustomizedMapper(); mapper.setCustomMapper(customizedMapper); } mappersRegistry.remove(mapper); //生成的mapper存放到mappersRegistry mappersRegistry.add(mapper); classMapRegistry.put(mapperKey, (ClassMap<Object, Object>) classMap); return mapper; }
MapperGenerator的build方法
public GeneratedMapperBase build(ClassMap<?, ?> classMap, MappingContext context) { StringBuilder logDetails = null; try { compilerStrategy.assureTypeIsAccessible(classMap.getAType().getRawType()); compilerStrategy.assureTypeIsAccessible(classMap.getBType().getRawType()); if (LOGGER.isDebugEnabled()) { logDetails = new StringBuilder(); String srcName = TypeFactory.nameOf(classMap.getAType(), classMap.getBType()); String dstName = TypeFactory.nameOf(classMap.getBType(), classMap.getAType()); logDetails.append("Generating new mapper for (" + srcName + ", " + dstName + ")"); } //构建用来生成源码及字节码的上下文 final SourceCodeContext mapperCode = new SourceCodeContext(classMap.getMapperClassName(), GeneratedMapperBase.class, context, logDetails); Set<FieldMap> mappedFields = new LinkedHashSet<FieldMap>(); //增加mapAtoB方法 mappedFields.addAll(addMapMethod(mapperCode, true, classMap, logDetails)); //增加mapBtoA方法 //addMapMethod方法基本就是手写代码的过程，有兴趣的读者可以看看 mappedFields.addAll(addMapMethod(mapperCode, false, classMap, logDetails)); //生成一个mapper实例 GeneratedMapperBase instance = mapperCode.getInstance(); instance.setAType(classMap.getAType()); instance.setBType(classMap.getBType()); instance.setFavorsExtension(classMap.favorsExtension()); if (logDetails != null) { LOGGER.debug(logDetails.toString()); logDetails = null; } classMap = classMap.copy(mappedFields); context.registerMapperGeneration(classMap); return instance; } catch (final Exception e) { if (logDetails != null) { logDetails.append("\n<---- ERROR occurred here"); LOGGER.debug(logDetails.toString()); } throw new MappingException(e); }
生成mapper实例
T instance = (T) compileClass().newInstance(); protected Class<?> compileClass() throws SourceCodeGenerationException { try { return compilerStrategy.compileClass(this); } catch (SourceCodeGenerationException e) { throw e; } }
这里的compilerStrategy的默认是用Javassist（你也可以自定义生成字节码的策略）
JavassistCompilerStrategy的compileClass方法
这基本上就是一个使用Javassist的过程，经过前面的各种铺垫（通过配置信息、上下文信息、拼装java源代码等等），终于来到这一步
public Class<?> compileClass(SourceCodeContext sourceCode) throws SourceCodeGenerationException { StringBuilder className = new StringBuilder(sourceCode.getClassName()); CtClass byteCodeClass = null; int attempts = 0; Random rand = RANDOM; while (byteCodeClass == null) { try { //创建一个类 byteCodeClass = classPool.makeClass(className.toString()); } catch (RuntimeException e) { if (attempts < 5) { className.append(Integer.toHexString(rand.nextInt())); } else { // No longer likely to be accidental name collision; // propagate the error throw e; } } } CtClass abstractMapperClass; Class<?> compiledClass; try { //把源码写到磁盘（通过上面提到的配置） writeSourceFile(sourceCode); Boolean existing = superClasses.put(sourceCode.getSuperClass(), true); if (existing == null || !existing) { classPool.insertClassPath(new ClassClassPath(sourceCode.getSuperClass())); } if (registerClassLoader(Thread.currentThread().getContextClassLoader())) { classPool.insertClassPath(new LoaderClassPath(Thread.currentThread().getContextClassLoader())); } abstractMapperClass = classPool.get(sourceCode.getSuperClass().getCanonicalName()); byteCodeClass.setSuperclass(abstractMapperClass); //增加字段 for (String fieldDef : sourceCode.getFields()) { try { byteCodeClass.addField(CtField.make(fieldDef, byteCodeClass)); } catch (CannotCompileException e) { LOG.error("An exception occurred while compiling: " + fieldDef + " for " + sourceCode.getClassName(), e); throw e; } } //增加方法，这里主要就是mapAtoB和mapBtoA方法 //直接用源码通过Javassist往类“加”方法 for (String methodDef : sourceCode.getMethods()) { try { byteCodeClass.addMethod(CtNewMethod.make(methodDef, byteCodeClass)); } catch (CannotCompileException e) { LOG.error( "An exception occured while compiling the following method:\n\n " + methodDef + "\n\n for " + sourceCode.getClassName() + "\n", e); throw e; } } //生成类 compiledClass = byteCodeClass.toClass(Thread.currentThread().getContextClassLoader(), this.getClass().getProtectionDomain()); //字节码文件写磁盘 writeClassFile(sourceCode, byteCodeClass); } catch (NotFoundException e) { throw new SourceCodeGenerationException(e); } catch (CannotCompileException e) { throw new SourceCodeGenerationException("Error compiling " + sourceCode.getClassName(), e); } catch (IOException e) { throw new SourceCodeGenerationException("Could not write files for " + sourceCode.getClassName(), e); } return compiledClass; }
好，mapper类生成了，现在就看在调用MapperFacade的map方法是如何使用这个mapper类的。
其实很简单，还记得生成的mapper是放到mappersRegistry吗，跟踪代码，在resolveMappingStrategy方法根据typeA和typeB在mappersRegistry找到mapper，在调用mapper的mapAtoB或mapBtoA方法即可。
小结
总体来说，Orika是一个功能强大的而且性能很高的工具，推荐使用。
总结
通过对BeanUtils、BeanCopier、Dozer、Orika这几个工具的对比，我们得知了它们的性能以及实现原理。在使用时，我们可以根据自己的实际情况选择，推荐使用Orika。
参考资料
打开 orika 的正确方式
