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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:

upload successful

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BeanInfoPropertyDescriptor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MapperFactoryMapperFacade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。

文章目录
  1. 1. 背景
  2. 2. 性能分析
  3. 3. Spring的BeanUtils
    1. 3.1. 使用
    2. 3.2. 原理
    3. 3.3. 小结
  4. 4. Apache的BeanUtils
    1. 4.1. 使用
    2. 4.2. 原理
    3. 4.3. 小结
  5. 5. BeanCopier
    1. 5.1. 使用
    2. 5.2. 原理
    3. 5.3. 小结
  6. 6. Dozer
    1. 6.1. 使用
    2. 6.2. 原理
    3. 6.3. 小结
  7. 7. Orika
    1. 7.1. 使用
  8. 8. 原理
  9. 9. 小结
  10. 10. 总结