莊周夢蝶

呵呵，在《develope J2EE without EJB》中，DTO被狠很地批判了一把，rod說這完全是反模式。可實際項目當中，我們還是不得不在使用。VO，PO，一牽扯到概念總是多么復雜。。。把一個PO從頭傳到尾？？從頁面到數據庫，一捅到底？NO，NO，萬一你要顯示給用戶的是幾個PO的結合怎么辦？萬一我們只是需要某幾個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據庫設計模型暴露給用戶。所以我們需要一些map工具來轉換，在這方面，過去我只知道有個 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。看看它支持的轉換類型：

? 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，它都提供了方法來做到。而且dozer可以很容易地跟spring集成。下面舉個簡單例子：

定義一個Book對象：

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;
?}
}
簡單的，我們要實例化一個對象，然后clone此對象，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，如此簡單，我們把book1的屬性完全復制給了book2，兩者現在是完全獨立的對象。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映射給一個完全不同的類的對象怎么辦？而且他們的屬性名也不相同，怎么辦？比如，一個CookBook類：

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，我們該如何復制？dozer通過xml文件的配置來靈活地達到這個目的。我們配置一個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>