呵呵，在《develope J2EE without EJB》中，DTO被狠很地批判了一把，rod说这完全是反模式。可实际项目当中，我们还是不得不在使用。VO，PO，一牵扯到概念总是多么复杂。。。把一个PO从头传到尾？？从页面到数据库，一捅到底？NO，NO，万一你要显示给用户的是几个PO的结合怎么办？万一我们只是需要某几个属性组合在一起显示怎么办？一捅到底的策略是多么丑陋，而且你完全把你的数据库设计模型暴露给用户。所以我们需要一些map工具来转换，在这方面，过去我只知道有个 BeanUtils，不够灵活，而今天，接触了下dozer，啊，跟spring一样的理念！灵活多变，你想怎么映射，想怎么换都可以。看看它支持的转换类型：
• Primitive to Primitive Wrapper
• Primitive to Custom Wrapper
• Primitive Wrapper to Primitive Wrapper
• Primitive to Primitive
• Complex Type to Complex Type
• String to Primitive
• String to Primitive Wrapper
• String to Complex Type if the Complex Type contains a String constructor
• Each of these can be mapped to one another: java.util.Date, java.sql.Date, java.sql.Time,
java.sql.Timestamp, java.util.Calendar, java.util.GregorianCalendar
• String to any of the supported Date/Calendar Objects if an explicit date format mapping attribute is
specified.
• Objects containing a toString() method that produces a long representing time in (ms) to any
supported Date/Calendar object.
几乎我们能想到的，它都提供了方法来做到。而且dozer可以很容易地跟spring集成。下面举个简单例子：
定义一个Book对象：
package com.denny_blue.dozerdemo;
public class Book {
private String name;
private String author;
public Book(){
}
public void setAuthor(String author) {
this.author = author;
}
public String getAuthor() {
return (this.author);
}
public void setName(String name){
this.name=name;
}
public String getName(){
return this.name;
}
}
简单的，我们要实例化一个对象，然后clone此对象，注意，是clone！
package com.denny_blue.dozerdemo;
import net.sf.dozer.util.mapping.DozerBeanMapper;
import java.util.List;
import java.util.ArrayList;
public class MyFirstDozerDemo {
public static void main(String args[]){
Book book1=new Book();
book1.setAuthor("dennis");
book1.setName("dozer demo");
DozerBeanMapper mapper=new DozerBeanMapper();
Book book2=new Book();
mapper.map(book1,book2);
book2=(Book)mapper.map(book1,com.denny_blue.dozerdemo.Book.class);
System.out.println("book2's name:"+book2.getName());
}
}
OK，如此简单，我们把book1的属性完全复制给了book2，两者现在是完全独立的对象。可如果仅仅是这样，我们用BeanUtils不是也很容易办到？ book2=(Book)BeanUtils.cloneBean(book1);可如果我要把book1映射给一个完全不同的类的对象怎么办？而且他们的属性名也不相同，怎么办？比如，一个CookBook类：
package com.denny_blue.dozerdemo;
public class CookBook {
private String bookName;
private String author;
public CookBook(){}
public String getBookName() {
return (this.bookName);
}
public void setBookName(String bookName) {
this.bookName = bookName;
}
public String getAuthor() {
return (this.author);
}
public void setAuthor(String author) {
this.author = author;
}
}
它的bookName属性与Book的name属性名不一样，我们该如何复制？dozer通过xml文件的配置来灵活地达到这个目的。我们配置一个dozerBeanMapping.xml：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mappings PUBLIC "-//DOZER//DTD MAPPINGS//EN"
"http://dozer.sourceforge.net/dtd/dozerbeanmapping.dtd">
<mappings>
<configuration>
<stop-on-errors>false</stop-on-errors>
<date-format>MM/dd/yyyy HH:mm</date-format>
<wildcard>true</wildcard>
</configuration>
<mapping>
<class-a>com.denny_blue.dozerdemo.Book</class-a>
<class-b>com.denny_blue.dozerdemo.CookBook</class-b>
<field>
<a>name</a>
<b>bookName</b>
</field>
<field>
<a>author</a>
<b>author</b>
</field>
</mapping>
</mappings>
如上所示，<class-a>指定所要复制的源对象，<class-b>复制的目标对象，<a>源对象的属性名， <b>目标对象的属性名。wildcard默认为true,在此时默认对所有属性进行map，如果为false，则只对在xml文件中配置的属性进行map。此时的demo 看起来像这样：
package com.denny_blue.dozerdemo;
import net.sf.dozer.util.mapping.DozerBeanMapper;
import java.util.List;
import java.util.ArrayList;
public class MyFirstDozerDemo {
public static void main(String args[]){
Book book1=new Book();
book1.setAuthor("dennis");
book1.setName("dozer demo");
DozerBeanMapper mapper=new DozerBeanMapper();
book2=(Book)mapper.map(book1,com.denny_blue.dozerdemo.Book.class);
CookBook cookBook=new CookBook();
List myMappingFiles = new ArrayList();
myMappingFiles.add("dozerBeanMapping.xml");
mapper.setMappingFiles(myMappingFiles);
cookBook=(CookBook)mapper.map(book1,CookBook.class);
System.out.println("cookBook's name:"+ cookBook.getBookName()+" cookBook's author:"+
cookBook.getAuthor());
}
}
通过mapper.setMappingFiles()设置映射文件，可以添加多个配置文件，也可以把所有的映射写在一个配置文件里面。 更多复杂例子请见它自带的doc
文章转自庄周梦蝶 ，原文发布时间5.17