应用 Castor 把 XML 转换成相应的 JavaBean(二) | 隔叶黄莺 Yanbin Blog

2011-04-23 | 阅读(1,015)

紧接前一篇应用 Castor 把 XML 转换成相应的 JavaBean(一)，本例稍显复杂一些，也就是要使用到映射文件，更复杂的 JavaBean、XML 数据类型和结构，引入自定的 FieldHandler，还有存在 Namespace 的情形。

关于如何使用 Castor 来把 XML 映射成 JavaBean 请着重阅读这个链接 http://www.castor.org/reference/html/XML%20data%20binding.html 中的内容，里面有说明支持的类型，如何定义自己的类型 Handler 及配置 Handler 的属性，mapping.xml 文件怎么写及各部份的意义；还有 castor.properties 的配置，比其中的 suppressNamespaces 为 true 时可以忽略掉 Namespace，默认为 false.

直接看例子吧：

1. persons.xml，这里放了一个 Namespace，并定义了一个 Address 类型，还使得节点名与 Bean 的属性名不一致：

<?xml version="1.0" encoding="UTF-8"?>
<Persons xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
    <Person i:Type="worker">
        <Name>Unmi</Name>
        <Address>st1|st2</Address>
    </Person>
    <Person i:Type="yuan">
        <Name>Fantasia</Name>
        <Address>sz|gd</Address>
    </Person>
</Persons>

<?xml version="1.0" encoding="UTF-8"?>

</Person>

<Name>Fantasia</Name>

</Person>

</Persons>

2. PersonList.java:

package cc.unmi.castor;

import java.util.List;

/**
 * @author Unmi Qiu
 * CreateTime: Apr 23, 2011
 */
public class PersonList {
    List<Person> persons;

    public List<Person> getPersons() {
        return persons;
    }

    public void setPersons(List<Person> persons) {
        this.persons = persons;
    }
}

package cc.unmi.castor;

import java.util.List;

/**

* @author Unmi Qiu

* CreateTime: Apr 23, 2011

public class PersonList {

List<Person> persons;

public List<Person> getPersons() {

return persons;

}

public void setPersons(List<Person> persons) {

this.persons = persons;

}

3. Person.java:

package cc.unmi.castor;


/**
 * @author Unmi Qiu
 * CreateTime: Apr 23, 2011
 */
public class Person {
    private String name;
    private Address address;
    private String type;

    //中间省去所有的 setter/getter 方法

    public String toString() {
        return name + "," + address + "," + type;
    }
}

package cc.unmi.castor;

/**

* @author Unmi Qiu

* CreateTime: Apr 23, 2011

public class Person {

private String name;

private Address address;

private String type;

//中间省去所有的 setter/getter 方法

public String toString() {

return name + "," + address + "," + type;

}

4. Address.java:

package cc.unmi.castor;

/**
 * @author Unmi Qiu
 * CreateTime: Apr 23, 2011
 */
public class Address {
    private String street1;
    private String street2;

    //中间省去所有的 setter/getter 方法

    public String toString() {
        return street1 + "|" + street2;
    }
}

package cc.unmi.castor;

/**

* @author Unmi Qiu

* CreateTime: Apr 23, 2011

public class Address {

private String street1;

private String street2;

//中间省去所有的 setter/getter 方法

public String toString() {

return street1 + "|" + street2;

}

5. AddressHandler.java，自定义的类型处理器，用于在 XML 与 Bean 属性间转换特定的类型：

package cc.unmi.castor;

import org.exolab.castor.mapping.FieldHandler;
import org.exolab.castor.mapping.ValidityException;

/**
 * Custom Address Handler
 * @author Unmi Qiu
 * CreateTime: Apr 23, 2011
 */
public class AddressHandler implements FieldHandler {
   
    public Object getValue(Object object) throws IllegalStateException {
        Person root = (Person)object;
        if(root.getAddress() == null){
            return null;
        }
        
        return root.getAddress().getStreet1()+"|" + root.getAddress().getStreet2();
    }

    public void setValue(Object object, Object value) throws IllegalStateException, IllegalArgumentException {
        Person root = (Person)object;
        
        Address address = new Address();
        String[] streets  = ((String)value).split("\\|");
        address.setStreet1(streets[0]);
        address.setStreet2(streets[1]);
        
        root.setAddress(address);
    }

    public void resetValue(Object object) throws IllegalStateException, IllegalArgumentException {
    }

    public void checkValidity(Object object) throws ValidityException, IllegalStateException {

    }

    public Object newInstance(Object parent) throws IllegalStateException {
        return null;
    }
}

package cc.unmi.castor;

import org.exolab.castor.mapping.FieldHandler;

import org.exolab.castor.mapping.ValidityException;

/**

* Custom Address Handler

* @author Unmi Qiu

* CreateTime: Apr 23, 2011

public class AddressHandler implements FieldHandler {

public Object getValue(Object object) throws IllegalStateException {

Person root = (Person)object;

if(root.getAddress() == null){

return null;

}

return root.getAddress().getStreet1()+"|" + root.getAddress().getStreet2();

}

public void setValue(Object object, Object value) throws IllegalStateException, IllegalArgumentException {

Person root = (Person)object;

Address address = new Address();

String[] streets = ((String)value).split("\\|");

address.setStreet1(streets[0]);

address.setStreet2(streets[1]);

root.setAddress(address);

}

public void resetValue(Object object) throws IllegalStateException, IllegalArgumentException {

}

public void checkValidity(Object object) throws ValidityException, IllegalStateException {

}

public Object newInstance(Object parent) throws IllegalStateException {

return null;

}

这个 Handler 可没有 JAXB 相对应的 Adapter 那么好理解，要复杂的多，习惯下吧。

6. mapping.xml，映射文件，应该能看到它所表达的意思：

<?xml version="1.0"?>
<!DOCTYPE mapping PUBLIC "-//EXOLAB/Castor Mapping DTD Version 1.0//EN"
                         "http://castor.org/mapping.dtd">

<mapping>
    <class name="cc.unmi.castor.PersonList">

        <field name="persons" collection="arraylist" type="cc.unmi.castor.Person">
            <bind-xml name="Person" node="element" />
        </field>
    </class>

    <class name="cc.unmi.castor.Person">
        <map-to xml="Person" />

        <field name="name" type="java.lang.String">
            <bind-xml name="Name" node="element" />
        </field>

        <field name="address" type="string" 
           handler="cc.unmi.castor.AddressHandler">
            <bind-xml name="Address" node="element"/>
        </field>

        <field name="type" type="java.lang.String">
            <bind-xml name="i:Type" QName-prefix="i" node="attribute"
                xmlns:i="http://www.w3.org/2001/XMLSchema-instance" />
        </field>
    </class>

</mapping>

<?xml version="1.0"?>

<!DOCTYPE mapping PUBLIC "-//EXOLAB/Castor Mapping DTD Version 1.0//EN"

"http://castor.org/mapping.dtd">

<bind-xml name="Person" node="element" />

</field>

</class>

<map-to xml="Person" />

<bind-xml name="Name" node="element" />

</field>

<field name="address" type="string"

handler="cc.unmi.castor.AddressHandler">

<bind-xml name="Address" node="element"/>

</field>

<bind-xml name="i:Type" QName-prefix="i" node="attribute"

xmlns:i="http://www.w3.org/2001/XMLSchema-instance" />

</field>

</class>

</mapping>

上面有几点得好好看清楚下：

1） class 节点用 name 指定类型
2） field 节点用 type 指定类型
3） node 属性有是 element 也有对应于 attribute
4） address 的 type 为 string，而不是 cc.unmi.castor.Address，写成后者会报错的。
5）对于 type 节点有 Namespace 时，写法确实很啰嗦的。不过如果在 castor.properties 的配置 suppressNamespaces 为 true 则可以忽略掉 Namespace。

7. Client.java，最后是客户端调用代码：

package cc.unmi.castor;

import java.io.InputStream;
import java.net.URL;

import org.exolab.castor.mapping.Mapping;
import org.exolab.castor.xml.Unmarshaller;
import org.xml.sax.InputSource;


public class Client {

    public static void main(String[] args) throws Exception{
        Mapping mapping = new Mapping();
        URL urlMapping = ClassLoader.getSystemResource("mapping.xml");
        mapping.loadMapping(urlMapping);
        Unmarshaller unmarshaller = new Unmarshaller(PersonList.class);
        unmarshaller.setMapping(mapping);
        
        InputStream xmlInputStream = ClassLoader.getSystemResourceAsStream("persons.xml");
        InputSource inputSource = new InputSource(xmlInputStream);
        PersonList personList = (PersonList)unmarshaller.unmarshal(inputSource);
        System.out.println(personList.getPersons());
    }
}

package cc.unmi.castor;

import java.io.InputStream;

import java.net.URL;

import org.exolab.castor.mapping.Mapping;

import org.exolab.castor.xml.Unmarshaller;

import org.xml.sax.InputSource;

public class Client {

public static void main(String[] args) throws Exception{

Mapping mapping = new Mapping();

URL urlMapping = ClassLoader.getSystemResource("mapping.xml");

mapping.loadMapping(urlMapping);

Unmarshaller unmarshaller = new Unmarshaller(PersonList.class);

unmarshaller.setMapping(mapping);

InputStream xmlInputStream = ClassLoader.getSystemResourceAsStream("persons.xml");

InputSource inputSource = new InputSource(xmlInputStream);

PersonList personList = (PersonList)unmarshaller.unmarshal(inputSource);

System.out.println(personList.getPersons());

}

执行上面的代码控制台输出结果为：

[Unmi,st1|st2,worker, Fantasia,sz|gd,yuan]

结果正确。

最后还是说要用好下 Castor，请仔细阅读 http://www.castor.org/reference/html/XML%20data%20binding.html。原以为 Castor 的资料比 JAXB 少，现在才知道错了。而且就这样稍加深入的了解了下，发现 Castor 确实够强悍的。

参考：1. http://www.castor.org/xml-mapping.html
             2. http://castor.org/spring-xml-intro.html
             3. http://www.castor.org/xml-framework.html
             4. http://www.castor.org/reference/html/XML%20data%20binding.html

本文链接 https://yanbin.blog/castor-xml-to-javabean-2/, 来自隔叶黄莺 Yanbin Blog

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