eclipselink，MOXy，JAXB，Json工具类

• 从String中转成JSON对象
  最近使用json来传递对象，JAXB，基于JAVA annotation，因此代码简洁，所以选用支持JAXB的MOXy，以前一直用google Gson，这个适合手动解析JSON，它在一些很大的JSON对象上速度很快，但是不利于快速开发，且维护复杂，代码不友好。

Gson中的fromJson 方法也可以解析简单对象，如{"type":0,"score":0.0}。但复杂对象，包含数组，内嵌其他对象，我没有成功。

第一次使用MOXy，版本2.5.0，解析JSON出错：

MOXy deserialization exception: A descriptor with default root element was not found in the project

 

网上查了下，statckoverflow的

http://stackoverflow.com/questions/14246033/moxy-deserialization-exception-a-descriptor-with-default-root-element-was-not-f

上面说是没有指定root属性：

public static <T>T fromJson(StreamSource streamSource, Class<?> cls, boolean hasRoot)

throws JAXBException, ClassCastException {

Map<String, Object> properties = new HashMap<String, Object>(2);

properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");

properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, hasRoot);//---->这个需要设为false

.createContext(new Class[] { cls }, properties);

Unmarshaller un = jc.createUnmarshaller();

JAXBElement<T> elem = (JAXBElement<T>) un.unmarshal(streamSource,cls);//-->当JSON不含root时，必须指定cls类型。所以，这里必须要用StreamSource，而不能直接用reader，否则没法指定cls类型。

return  (T)(elem.getValue());

 

}

import java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.Unmarshaller;
import javax.xml.transform.stream.StreamSource;

import org.eclipse.persistence.jaxb.JAXBContextProperties;

public class DtoUtil {
	@SuppressWarnings("unchecked")
	public static <T>T fromJson(StreamSource streamSource, Class<?> cls, boolean hasRoot)
			throws JAXBException, ClassCastException {
		Map<String, Object> properties = new HashMap<String, Object>(2);
		properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");
		properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, hasRoot);
		JAXBContext jc = org.eclipse.persistence.jaxb.JAXBContextFactory
				.createContext(new Class[] { cls }, properties);
		Unmarshaller un = jc.createUnmarshaller();
		JAXBElement<T> elem = (JAXBElement<T>) un.unmarshal(streamSource,cls);
		return  (T)(elem.getValue());
	}
	public static <T> String toJson(T obj,Class<?>cls,boolean hasRoot) throws JAXBException,
			ClassCastException {
		Map<String, Object> properties = new HashMap<String, Object>(2);
		properties.put(JAXBContextProperties.MEDIA_TYPE, "application/json");
		properties.put(JAXBContextProperties.JSON_INCLUDE_ROOT, hasRoot);
		JAXBContext jc = org.eclipse.persistence.jaxb.JAXBContextFactory
				.createContext(new Class[] { cls }, properties);
		Marshaller marshaller = jc.createMarshaller();
		StringWriter writer = new StringWriter();
		marshaller.marshal(obj, writer);
		return writer.toString();
	}
}

 

 

maven dependency：

<dependency>

<groupId>org.eclipse.persistence</groupId>

<artifactId>eclipselink</artifactId>

<version>2.5.0</version>

</dependency>

 

用法，如：

DtoUtil.fromJson(new StreamSource(reader), cls, hasRoot);

DtoUtil.toJson(obj, cls, hasRoot);