莊周夢(mèng)蝶

呵呵，在《develope J2EE without EJB》中，DTO被狠很地批判了一把，rod說(shuō)這完全是反模式。可實(shí)際項(xiàng)目當(dāng)中，我們還是不得不在使用。VO，PO，一牽扯到概念總是多么復(fù)雜。。。把一個(gè)PO從頭傳到尾？？從頁(yè)面到數(shù)據(jù)庫(kù)，一捅到底？NO，NO，萬(wàn)一你要顯示給用戶的是幾個(gè)PO的結(jié)合怎么辦？萬(wàn)一我們只是需要某幾個(gè)屬性組合在一起顯示怎么辦？一捅到底的策略是多么丑陋，而且你完全把你的數(shù)據(jù)庫(kù)設(shè)計(jì)模型暴露給用戶。所以我們需要一些map工具來(lái)轉(zhuǎn)換，在這方面，過(guò)去我只知道有個(gè) BeanUtils，不夠靈活，而今天，接觸了下dozer，啊，跟spring一樣的理念！靈活多變，你想怎么映射，想怎么換都可以。看看它支持的轉(zhuǎn)換類(lèi)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.

幾乎我們能想到的，它都提供了方法來(lái)做到。而且dozer可以很容易地跟spring集成。下面舉個(gè)簡(jiǎn)單例子：

定義一個(gè)Book對(duì)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;
?}
}
簡(jiǎn)單的，我們要實(shí)例化一個(gè)對(duì)象，然后clone此對(duì)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，如此簡(jiǎn)單，我們把book1的屬性完全復(fù)制給了book2，兩者現(xiàn)在是完全獨(dú)立的對(duì)象。可如果僅僅是這樣，我們用BeanUtils不是也很容易辦到？ book2=(Book)BeanUtils.cloneBean(book1);可如果我要把book1映射給一個(gè)完全不同的類(lèi)的對(duì)象怎么辦？而且他們的屬性名也不相同，怎么辦？比如，一個(gè)CookBook類(lèi)：

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屬性與Book的name屬性名不一樣，我們?cè)撊绾螐?fù)制？dozer通過(guò)xml文件的配置來(lái)靈活地達(dá)到這個(gè)目的。我們配置一個(gè)dozerBeanMapping.xml：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mappings PUBLIC "-//DOZER//DTD MAPPINGS//EN"
"<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>