SpringBoot学习小结之Dozer

前言

Dozer是一个Java Bean到Java Bean的Mapper，可将数据从一个对象递归复制到另一个对象。Dozer支持简单属性、复杂属性映射，Java中常见集合相互映射和递归映射。

Dozer可以看做是一个对象属性拷贝工具，适用于模型转换，同样的工具还有很多，例如Cglib的BeanCopier、Apache 的PropertyUtils、Spring的BeanUtils。

Dozer与上述工具相比，最大的优势就是支持不同名属性映射。当然，最大的劣势就是性能差。这里附上一张其他博主做性能测试的表格。相关博文

类	方法	归属	单次耗时[ms]	100万次耗时[ms]	平均耗时[ms]
BeanCopier	copy	Cglib	0.005071	58.415201	0.000058
BeanUtils	copyProperties	Spring	0.072082	2155.744378	0.002155
PropertyUtils	copyProperties	Apache	0.164118	16714.877932	0.016714
DozerBeanMapper	map	Dozer	0.598338	19158.842820	0.019158

所以，当系统数据量不大、对性能要求不高，或者需要非同名属性映射时可以考虑使用Dozer。

springboot使用dozer pom依赖。

<dependency><groupId>com.github.dozermapper</groupId><artifactId>dozer-spring-boot-starter</artifactId><version>6.5.0</version>
</dependency>

一、Configuration配置

简单配置

application.yml
```
dozer:mapping-files: classpath:dozer/first.xml
```
dozer.mapping-files是dozer-spring-boot-start自带属性，可以通过application.yml配置，多个用逗号隔开

通配符配置

默认不支持通配符配置，需要编写配置文件

dozer:mapping-files: classpath:dozer/*.xml

@Configuration
public class DozerConfig {@Beanpublic DozerBeanMapperFactoryBean dozerMapper(@Value("${dozer.mapping-files}") Resource[] resources) throws IOException {DozerBeanMapperFactoryBean dozerBeanMapperFactoryBean = new DozerBeanMapperFactoryBean();dozerBeanMapperFactoryBean.setMappingFiles(resources);return dozerBeanMapperFactoryBean;}
}

mapping配置文件示例

<?xml version="1.0" encoding="UTF-8"?>
<mappings xmlns="http://dozermapper.github.io/schema/bean-mapping"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://dozermapper.github.io/schema/bean-mapping http://dozermapper.github.io/schema/bean-mapping.xsd"><mapping><class-a>org.dozer.vo.TestObject</class-a><class-b>org.dozer.vo.TestObjectPrime</class-b><field><a>one</a><b>onePrime</b></field></mapping>
</mappings>

二、工具类

@Component
public class DozerUtil {private static Mapper dozerMapper;@Autowiredpublic void setDozerMapper(Mapper dozerMapper) {DozerUtil.dozerMapper = dozerMapper;}/*** 构造新的destinationClass实例对象，通过source对象中的字段内容* 映射到destinationClass实例对象中，并返回新的destinationClass实例对象。** @param source           源数据对象* @param destinationClass 要构造新的实例对象Class*/public static <T> T map(Object source, Class<T> destinationClass) {return dozerMapper.map(source, destinationClass);}/*** 将对象source的所有属性值拷贝到对象destination中.** @param source            对象source* @param destinationObject 对象destination*/public static void map(Object source, Object destinationObject) {dozerMapper.map(source, destinationObject);}/*** List数据源映射** @param sourceList* @param destinationClass* @param <T>* @return List<T>*/public static <T> List<T> mapList(Collection sourceList, Class<T> destinationClass) {List destinationList = new ArrayList<>();for (Iterator iterator = sourceList.iterator(); iterator.hasNext(); ) {Object sourceObject = iterator.next();Object destinationObject = dozerMapper.map(sourceObject, destinationClass);destinationList.add(destinationObject);}return destinationList;}

三、常用的几种映射

Bean到Bean

Bean和Bean之间映射，这是最常见的映射。Dozer默认同名映射，即不用配置文件就可以实现Bean之间的同名映射。使用Mapping配置文件即可实现非同名属性的映射。
Bean List到Bean List

实际上还是Bean之间的映射，将srcList中Bean映射完后装入destList中

Date到String

单个字段

<field><a date-format="yyyy-MM-dd HH:mm:ss">dateObject</a><b>dateString</b>
</field>

单个类所有Date字段

<mapping date-format="yyyy-MM-dd HH:mm:ss">
</mapping>

HashMap到Bean

hashMap可以通过将key配置成Bean的field名，和Bean映射

四、高级功能

自定义转换器

自定义类型转换器需要实现com.github.dozermapper.core.CustomConverter接口或者继承com.github.dozermapper.core.DozerConverter类

以CustomConverter示例：Enum映射String

public enum Color {RED("red"), GREEN("green"), YELLOW("yellow");private String value;Color(String value) {this.value = value;}public static Color newInstance(String color) throws Exception {switch (color) {case "red" : return RED;case "green": return GREEN;case "yellow": return YELLOW;default: throw new Exception("unknow color:" + color);}}@Overridepublic String toString() {return value;}
}

@Data
public class FlowerVo {private Integer id;private String purchaseDateStr;private String colorStr;
}

@Data
public class Flower {private Integer id;private Date purchaseDate;private Color color;
}

public class EnumColorCustomConverter implements CustomConverter {@Overridepublic Object convert(Object existingDestinationFieldValue, Object sourceFieldValue, Class<?> destinationClass, Class<?> sourceClass) {if (sourceFieldValue == null) {return null;}if (sourceFieldValue instanceof Color) {return sourceFieldValue.toString();} if (sourceFieldValue instanceof String && destinationClass.equals(Color.class)) {try {return Color.newInstance((String)sourceFieldValue);} catch (Exception e) {e.printStackTrace();}} else{throw new MappingException("Converter EnumColorCustomConverter "+ "used incorrectly. Arguments passed in were:"+ sourceFieldValue);}return  null;}
}

<mapping><class-a>com.aabond.entity.Flower</class-a><class-b>com.aabond.entity.FlowerVo</class-b><field><a >purchaseDate</a><b date-format="yyyy-MM-dd HH:mm:ss">purchaseDateStr</b></field><field custom-converter="com.aabond.converter.EnumColorCustomConverter"><a>color</a><b>colorStr</b></field>
</mapping>

@Test
public void testDozer() {Flower flower = new Flower();flower.setId(1);flower.setPurchaseDate(new Date());flower.setColor(Color.RED);FlowerVo f = DozerUtil.map(flower, FlowerVo.class);System.out.println(f);//assertThat(map, isA(Flower.class));}

更多配置
关于XML配置,更详细信息可以查看官方文档，下面介绍一些常用的配置

Date和String 全局映射

<mappings><configuration><date-format>yyyy-MM-dd HH:mm:ss</date-format><!-- more --></configuration>
</mappings>

遇到错误策略默认true
```
<stop-on-errors>true</stop-on-errors>
```
同名属性映射默认true
```
<wildcard>true</wildcard>
```
字符串Trim
```
<trim-strings>false</trim-strings>
```

全局自定义转换器

<custom-converters> <converter type="org.dozer.converters.TestCustomConverter" ><class-a>org.dozer.vo.TestCustomConverterObject</class-a><class-b>another.type.to.Associate</class-b></converter>
</custom-converters>

null值不映射

<field map-null="false"><a>oneFoo2</a><b>oneFooPrime2</b>
</field>

单项映射
dozer默认是双向映射，可以通过配置改成单项映射
- 支持字段单项映射
```
<field type="one-way"><a>oneFoo2</a><b>oneFooPrime2</b>
</field>
```
- 支持类单项映射
```
<mapping type="one-way">
</mapping>
```

复制引用

Dozer支持复制引用

<field copy-by-reference="true"><a>copyByReference</a><b>copyByReferencePrime</b>
</field>

支持全局配置

<configuration><copy-by-references><copy-by-reference>com.github.dozermapper.core.vo.NoExtendBaseObjectGlobalCopyByReference</copy-by-reference></copy-by-references>
</configuration>

参考：

https://blog.csdn.net/u012534326/article/details/102611483
http://dozer.sourceforge.net/dozer-user-guide.pdf
https://dozermapper.github.io/gitbook/