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起源：https://albenw.github.io/post…
背景
在分层的代码架构中，层与层之间的对象防止不了要做很多转换、赋值等操作，这些操作反复且繁琐，于是乎催生出很多工具来优雅，高效地实现这个操作，有 BeanUtils、BeanCopier、Dozer、Orika 等等，本文将讲述下面几个工具的应用、性能比照及原理剖析。
性能剖析
其实这几个工具要做的事件很简略，而且在应用上也是相似的，所以我感觉先给大家看看性能剖析的比照后果，让大家有一个大略的意识。我是应用 JMH 来做性能剖析的，代码如下：
要复制的对象比较简单，蕴含了一些根本类型；有一次 warmup，因为一些工具是须要“预编译”和做缓存的，这样做比照才会比拟主观；别离复制 1000、10000、100000 个对象，这是比拟罕用数量级了吧。
@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 下运行后的后果如下：
Score 示意的是均匀运行工夫，单位是微秒。从执行效率来看，能够看出 beanCopier > orika > springBeanUtil > dozer > apacheBeanUtil。这样的后果跟它们各自的实现原理有很大的关系，
上面将具体每个工具的应用及实现原理。
Spring 的 BeanUtils
应用
这个工具可能是大家日常应用最多的，因为是 Spring 自带的，应用也简略：BeanUtils.copyProperties(sourceVO, targetVO);
原理
Spring BeanUtils 的实现原理也比拟简答，就是通过 Java 的 Introspector 获取到两个类的PropertyDescriptor，比照两个属性具备雷同的名字和类型，如果是，则进行赋值（通过 ReadMethod 获取值，通过 WriteMethod 赋值），否则疏忽。
为了进步性能 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 办法入参和 source 的 getter 办法返回类型是否统一
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，这也是它性能比拟高的起因。
不过，过于简洁就失去了灵活性和可扩展性了，Spring BeanUtils 的应用限度也比拟显著，要求类属性的名字和类型统一，这点在应用时要留神。
Apache 的 BeanUtils
应用
Apache 的 BeanUtils 和 Spring 的 BeanUtils 的应用是一样的：
BeanUtils.copyProperties(targetVO, sourceVO); 要留神，source 和 target 的入参地位不同。
原理
Apache 的 BeanUtils 的实现原理跟 Spring 的 BeanUtils 一样，也是次要通过 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，然而 Apache BeanUtils 加了一些不那么应用的个性（包含反对 Map 类型、反对自定义的 DynaBean 类型、反对属性名的表达式等等）在外面，使得性能绝对 Spring 的 BeanUtils 来说有所降落。
（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());
}
}
// 规范的 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 总体上相似，然而性能却低很多，这个能够从下面性能比拟看进去。阿里的 Java 标准是不倡议应用的。
BeanCopier
应用
BeanCopier 在 cglib 包里，它的应用也比较简单：
@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));
} 只须要事后定义好要转换的 source 类和 target 类就好了，能够抉择是否应用Converter，这个上面会说到。
在下面的性能测试中，BeanCopier 是所有中体现最好的，那么咱们剖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，而是间接应用 cglib 来生成带有的 get/set 办法的 class 类，而后执行。因为是间接生成字节码执行，所以 BeanCopier 的性能靠近手写
get/set。
BeanCopier.create 办法
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 创立一个 BeanCopier 进去，而后调用 create 办法来生成字节码。
KEY_FACTORY 其实就是用 cglib 通过 BeanCopierKey 接口生成进去的一个类
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"); 能够让 cglib 输入生成类的 class 文件，咱们能够反编译看看外面的代码
上面是 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 等办法。。。} 持续跟踪 Generator.create 办法，因为 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 办法，最终会调用到 Generator 的模板办法 generateClass 办法，咱们不去细究 AbstractClassGenerator 的细节，重点看 generateClass。
这个是一个生成 java 类的办法，了解起来就如同咱们平时写代码一样。
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”一个办法，办法名是 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];
// 依据 setter 的 name 获取 getter
PropertyDescriptor getter = (PropertyDescriptor)names.get(setter.getName());
if (getter != null) {
// 获取读写办法
MethodInfo read = ReflectUtils.getMethodInfo(getter.getReadMethod());
MethodInfo write = ReflectUtils.getMethodInfo(setter.getWriteMethod());
// 如果用了 useConverter，则进行上面的拼装代码形式
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 是否类型统一
} 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());
} 即便没有应用过 cglib 也能读懂生成代码的流程吧，咱们看看没有应用 useConverter 的状况下生成的代码：
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());
}
} 在比照下面生成代码的代码是不是阔然开朗了。
再看看应用 useConverter 的状况：
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 性能的确很高，但从源码能够看出 BeanCopier 只会拷贝名称和类型都雷同的属性，而且如果一旦应用 Converter，BeanCopier 只应用 Converter 定义的规定去拷贝属性，所以在 convert 办法中要思考所有的属性。
Dozer
应用
下面提到的 BeanUtils 和 BeanCopier 都是性能比较简单的，须要属性名称一样，甚至类型也要一样。然而在大多数状况下这个要求就绝对刻薄了，要晓得有些 VO 因为各种起因不能批改，有些是内部接口 SDK 的对象，
有些对象的命名规定不同，例如有驼峰型的，有下划线的等等，各种什么状况都有。所以咱们更加须要的是更加灵便丰盛的性能，甚至能够做到定制化的转换。
Dozer 就提供了这些性能，有反对同名隐式映射，反对根本类型相互转换，反对显示指定映射关系，反对 exclude 字段，反对递归匹配映射，反对深度匹配，反对 Date to String 的 date-formate，反对自定义转换 Converter，反对一次 mapping 定义多处应用，反对 EventListener 事件监听等等。不仅如此，Dozer 在应用形式上，除了反对 API，还反对 XML 和注解，满足大家的爱好。更多的性能能够参考这里
因为其性能很丰盛，不可能每个都演示，这里只是给个大略意识，更具体的性能，或者 XML 和注解的配置，请看官网文档。
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 的实现原理实质上还是用反射 /Introspector 那套，然而其丰盛的性能，以及反对多种实现形式（API、XML、注解）使得代码看上去有点简单，在翻阅代码时，咱们大可不必理睬这些类，只须要晓得它们大体的作用就行了，重点关注外围流程和代码的实现。上面咱们重点看看构建 mapper 的 build 办法和实现映射的 map 办法。
build 办法很简略，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前面要用到的配置对象、上下文对象，或其余封装对象，咱们不用深究这些对象是怎么实现的，从名字上咱们大略能猜出这些对象是干嘛，负责什么就能够了。
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 办法是映射对象的过程，其入口是 MappingProcessor 的 mapGeneral 办法
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 是包含 src 类和 dest 类和其余配置的一个封装
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;
}
}
// 优先应用自定义 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());
// 持续进行映射
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;
} 个别状况下 createByCreationDirectiveAndMap 办法会始终调用到 mapFromFieldMap 办法，而在没有自定义 converter 的状况下会调用 mapOrRecurseObject 办法
大多数状况下字段的映射会在这个办法做个别的解析
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 的解决
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;}
}
// 如果只是浅拷贝则间接返回（可配置）if (fieldMap.isCopyByReference()) {
// just get the src and return it, no transformation.
return srcFieldValue;
}
// 对 Map 类型的解决
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;
}
// 对根本类型的映射解决
//PrimitiveOrWrapperConverter 类反对兼容了根本类型之间的相互转换
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);
}
}
// 对汇合类型的映射解决
if (MappingUtils.isSupportedCollection(srcFieldClass) && (MappingUtils.isSupportedCollection(destFieldType))) {return mapCollection(srcObj, srcFieldValue, fieldMap, destObj);
}
// 对枚举类型的映射解决
if (MappingUtils.isEnumType(srcFieldClass, destFieldType)) {return mapEnum((Enum)srcFieldValue, (Class<Enum>)destFieldType);
}
if (fieldMap.getDestDeepIndexHintContainer() != null) {destFieldType = fieldMap.getDestDeepIndexHintContainer().getHint();}
// 其余简单对象类型的解决
return mapCustomObject(fieldMap, destObj, destFieldType, destFieldName, srcFieldValue);
} mapCustomObject 办法。其实你会发现这个办法最重要的一点就是做递归解决，无论是最初调用 createByCreationDirectiveAndMap 还是 mapToDestObject 办法。
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体现个别，仅次于 Apache 的 BeanUtils。如果不谋求性能的话，能够应用。
Orika
Orika 能够说是简直集成了上述几个工具的长处，不仅具备丰盛的性能，底层应用 Javassist 生成字节码，运行 效率很高的。
应用
Orika 根本反对了 Dozer 反对的性能，这里我也是简略介绍一下 Orika 的应用，具体更具体的 API 能够参考 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
在解说实现原理时，咱们先看看 Orika 在背地干了什么事件。
通过减少以下配置，咱们能够看到 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"); 用下面的例子，咱们看看 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 类就两个办法 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，咱们们看看实现的过程。
Orika 的应用跟 Dozer 的相似，首先通过配置生成一个 MapperFactory，再用MapperFacade 来作为映射的对立入口，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 办法时才初始化 mapper。上面看看 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 上下文信息来结构 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
// 在应用 mapperFactory 配置 classMap 时，会寄存在 classMapRegistry 里
for (ClassMap<?, ?> classMap : classMapRegistry.values()) {
// 对每个 classMap 生成一个 mapper，重点看 buildMapper 办法
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 办法
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 办法生成 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 寄存到 mappersRegistry
mappersRegistry.add(mapper);
classMapRegistry.put(mapperKey, (ClassMap<Object, Object>) classMap);
return mapper;
} MapperGenerator 的 build 办法
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>();
// 减少 mapAtoB 办法
mappedFields.addAll(addMapMethod(mapperCode, true, classMap, logDetails));
// 减少 mapBtoA 办法
//addMapMethod 办法根本就是手写代码的过程，有趣味的读者能够看看
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（你也能够自定义生成字节码的策略）
JavassistCompilerStrategy 的 compileClass 办法
这基本上就是一个应用 Javassist 的过程，通过后面的各种铺垫（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 {
// 创立一个类
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（通过下面提到的配置）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);
// 减少字段
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;
}
}
// 减少办法，这里次要就是 mapAtoB 和 mapBtoA 办法
// 间接用源码通过 Javassist 往类“加”办法
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，当初就看在调用 MapperFacade 的 map 办法是如何应用这个 mapper 类的。
其实很简略，还记得生成的 mapper 是放到 mappersRegistry 吗，跟踪代码，在 resolveMappingStrategy 办法依据 typeA 和 typeB 在 mappersRegistry 找到 mapper，在调用 mapper 的 mapAtoB 或 mapBtoA 办法即可。
小结
总体来说，Orika 是一个功能强大的而且性能很高的工具，举荐应用。
总结
通过对 BeanUtils、BeanCopier、Dozer、Orika 这几个工具的比照，咱们得悉了它们的性能以及实现原理。在应用时，咱们能够依据本人的理论状况抉择，举荐应用 Orika。
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