JAXB是很强大的
XML <--> Java Class映射工具。很可惜它默认不支持对Hashmap的映射。但我们可以通过使用XmlJavaTypeAdapter来扩展实现,本文介绍详细方法。
首先创建一个带有HashMap的Class:
package net.bluedash;
import java.util.HashMap;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Foo {
@XmlJavaTypeAdapter(MyHashMapAdapter.class)
HashMap hashmap;
public Foo() {
hashmap = new HashMap();
}
public HashMap getHashmap() {
return hashmap;
}
public void setHashmap(HashMap hashmap) {
this.hashmap = hashmap;
}
}
我们使用自己的MyHashMapAdapter.class来映射HashMap:
package net.bluedash;
import java.util.HashMap;
import java.util.List;
import java.util.Set;
import java.util.Map.Entry;
import javax.xml.bind.annotation.adapters.XmlAdapter;
public final class MyHashMapAdapter extends XmlAdapter<MyHashMapType, HashMap> {
@Override
public MyHashMapType marshal(HashMap arg0) throws Exception {
MyHashMapType myHashMapType = new MyHashMapType();
for (Entry entry : (Set<Entry>) arg0.entrySet()) {
MyHashEntryType myHashEntryType = new MyHashEntryType();
myHashEntryType.key = (Integer) entry.getKey();
myHashEntryType.value = (String) entry.getValue();
myHashMapType.entries.add(myHashEntryType);
// myHashMapType = myHashEntryType;
}
return myHashMapType;
}
@Override
public HashMap unmarshal(MyHashMapType arg0) throws Exception {
HashMap hashMap = new HashMap();
for (MyHashEntryType myHashEntryType : (List<MyHashEntryType>) arg0.entries) {
hashMap.put(myHashEntryType.key, myHashEntryType.value);
}
return hashMap;
}
}
里面使用了
自定义的MyHashMapType:
package net.bluedash;
import java.util.ArrayList;
import java.util.List;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
@XmlRootElement
public class MyHashMapType {
@XmlElement(required = true)
public List<MyHashEntryType> entries = new ArrayList<MyHashEntryType>();
}
使用MyHashEntryType来实现对HashMap每一条数据的映射:
package net.bluedash;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlType;
import javax.xml.bind.annotation.XmlValue;
@XmlAccessorType(XmlAccessType.FIELD)
@XmlType
public class MyHashEntryType {
@XmlAttribute
public Integer key;
@XmlValue
public String value;
}
下面做一个Demo来使用一下我们的Adapter:
package net.bluedash;
import java.io.File;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
public class App {
public static void main(String[] args) throws JAXBException {
JAXBContext jaxbContext = JAXBContext.newInstance(Foo.class);
Foo foo = new Foo();
foo.getHashmap().put(1, "One");
foo.getHashmap().put(2, "Two");
foo.getHashmap().put(3, "Three");
Marshaller marshaller = jaxbContext.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
// Output the generated XML:
marshaller.marshal(foo, System.out);
// Save the output to a foo.xml
File xmlFile = new File("foo.xml");
marshaller.marshal(foo, xmlFile);
// Restore the Foo class from xml file
Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
Foo createdFoo = (Foo) unmarshaller.unmarshal(xmlFile);
// See the result
System.out.println(createdFoo.hashmap);
}
}
代码运行结果如下:
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<foo>
<hashmap>
<entries key="1">One</entries>
<entries key="2">Two</entries>
<entries key="3">Three</entries>
</hashmap>
</foo>
{1=One, 2=Two, 3=Three}
我将上面的
例子放在了github上面,可以取下来动手玩玩看:
% git clone git://github.com/liweinan/jaxb-hashmap.git
执行下述
Maven命令运行:
mvn exec:java -Dexec.mainClass="net.bluedash.App"