实现bean动态生成xml报文（只需修改bean上变量的标签，不用修改别的代码）

最近项目中需要调用webService接口，请求时会传送xml报文，查阅了网上很多资料发现每次不一样的xml格式都需要修改生成xml的方法里的代码，并没有真正的做到通过bean来动态生成xml报文，因此现开发一个不需要修改生成xml的方法来动态生成xml报文(提示：此方法只适合三层嵌套的xml报文，如需更多嵌套则需要进行改进)

1.添加所需的包

		<dependency>
	            <groupId>org.jdomgroupId>
	            <artifactId>jdomartifactId>
	            <version>2.0.2version>
	    dependency>

2.编写能够判断xml层级的标签（可自己随意命名做区分）

• 生成Root标签类，来代表当前bean里的变量哪一个是根节点

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

//这里注意:RetentionPolicy需要手动导包
@Retention(RetentionPolicy.RUNTIME)
public @interface Root {

}

• 生成First标签类，来代表当前bean里的变量哪一个是子节点

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy.RUNTIME)
public @interface First {

}

3.编写动态生成xml的代码

import java.util.HashMap;
import java.util.Map;
import java.io.ByteArrayOutputStream;
import java.lang.reflect.Field;

import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.output.Format;
import org.jdom2.output.XMLOutputter;

import com.annotation.First;
import com.annotation.Root;
import com.entity.NodeInfo;


public class BeanToXmlUtil {

	/**
	 * 通过bean自动生成xml(只满足于三层)
	 * @param t
	 * @return
	 * @throws IllegalArgumentException
	 * @throws IllegalAccessException
	 */
	public  <T> String beanToXml(T t) throws IllegalArgumentException, IllegalAccessException {
		String xml = "";
		Element xmlRoot = null;
		Class<?> xmlClass = t.getClass();
		Map<String,NodeInfo> firstMap = new HashMap<String,NodeInfo>();
		for(Field field : xmlClass.getDeclaredFields()){
			field.setAccessible(true); // true 能够取到到类中的私有属性,默认为false
			if(field.isAnnotationPresent(Root.class)){
				xmlRoot = new Element(field.getName());
			}
			if(field.isAnnotationPresent(First.class)){ 
				NodeInfo nodeInfo = new NodeInfo();
				nodeInfo.setParent(xmlRoot.getName());
				nodeInfo.setValue(field.get(t));
				firstMap.put(field.getName(), nodeInfo);
			}
		}
		for (Map.Entry<String, NodeInfo> entry : firstMap.entrySet()) {
			Element element = new Element(entry.getKey());
			if(!((entry.getValue().getValue()) instanceof String)){
				for(Field fNode : entry.getValue().getValue().getClass().getDeclaredFields()){
					fNode.setAccessible(true);
					if(fNode.isAnnotationPresent(First.class)){
						Element elementNode = new Element(fNode.getName());
						elementNode.setText((String) fNode.get(entry.getValue().getValue()));
						element.addContent(elementNode);
					}
				}
			}else{
				element.setText((String)entry.getValue().getValue());
			}
			xmlRoot.addContent(element);
	    }
		Document doc = new Document(xmlRoot);
		XMLOutputter out = new XMLOutputter();
		Format format = Format.getCompactFormat();
		format.setEncoding("UTF-8");
		format.setIndent("\t");
		out.setFormat(format);// 设置文件编码，默认为UTF-8
		ByteArrayOutputStream bo = new ByteArrayOutputStream();
		try {
			out.output(doc, bo);
			xml = new String(bo.toByteArray(), "UTF-8");
		} catch (Exception e) {
			e.printStackTrace();;
		}
		return xml;
	}
}

//记录节点的相关信息
public class NodeInfo {

	private Object value;
	private String parent;
	
	public String getParent() {
		return parent;
	}
	public void setParent(String parent) {
		this.parent = parent;
	}
	public Object getValue() {
		return value;
	}
	public void setValue(Object value) {
		this.value = value;
	}	
}

4.测试bean

import com.annotation.First;
import com.annotation.Root;

public class TestXml {
	
	@Root
	private String Xml;
	
	@First
	private UserData userData;
	
	@First
	private String ext;

	public String getXml() {
		return Xml;
	}

	public void setXml(String xml) {
		Xml = xml;
	}

	public UserData getUserData() {
		return userData;
	}

	public void setUserData(UserData userData) {
		this.userData = userData;
	}

	public String getExt() {
		return ext;
	}

	public void setExt(String ext) {
		this.ext = ext;
	}
}

import com.annotation.First;

public class UserData {

	@First
	private String name;
	
	@First
	private String age;

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getAge() {
		return age;
	}

	public void setAge(String age) {
		this.age = age;
	}
	
}

5.进行测试

public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException {
	TestXml testXml= new TestXml();
	UserData userData = new UserData();
	userData.setName("xxp");
	userData.setAge("18");
	testXml.setExt("xxp is 18");
	testXml.setUserData(userData);
	BeanToXmlUtil.beanToXml(testXml);
	
}

结果

6.总结

优点：此篇方法能只修改bean上的标签来动态生成xml，无需修改生成xml中的代码

缺点：多层（3层以上）嵌套的问题，需要改进代码，深度大的话要不断的进行遍历

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