JAXB2 性能优化

jaxb2 实体类转xml

    public static String toXML(Object obj, String encode, boolean format, boolean fragment) {
        try {
            JAXBContext.newInstance(obj.getClass());
            Marshaller marshaller = jaxbContext.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_ENCODING, encode);           // 编码格式
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, format);   // 是否格式化生成的xml串
            marshaller.setProperty(Marshaller.JAXB_FRAGMENT, fragment);         // 是否省略xm头声明信息
            StringWriter writer = new StringWriter();
            marshaller.marshal(obj, writer);
            return writer.toString();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

jaxb2 xml转实体类

public static <T> T fromXML(String xml, Class<T> valueType) {
        try {
            JAXBContext jaxbContext = JAXBContext.newInstance(valueType);
            Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
            return (T) unmarshaller.unmarshal(new StringReader(xml));
        } catch (Exception e) {
            throw new RuntimeException(e.getMessage());
        }
    }

　　经测试，改两个方法，当调用次数达到一定量的时候，耗时从3ms到33ms，性能急剧下降。经分析发现，是由于JAXBContext.newInstance()方法导致的下降。
　　方法改造如下：

    static Map<String, JAXBContext> jaxbContextMap = new HashMap<String, JAXBContext>();

    /**
     * java实体类转xml
     */
    public static String toXML(Object obj, String encode, boolean format, boolean fragment) {
        try {
            JAXBContext jaxbContext = jaxbContextMap.get(obj.getClass().getName());
            if(jaxbContext == null){
                // 如果每次都调用JAXBContext.newInstance方法，会导致性能急剧下降
                jaxbContext = JAXBContext.newInstance(obj.getClass());
                jaxbContextMap.put(obj.getClass().getName(), jaxbContext);
            }

            Marshaller marshaller = jaxbContext.createMarshaller();
            marshaller.setProperty(Marshaller.JAXB_ENCODING, encode);           // 编码格式
            marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, format);   // 是否格式化生成的xml串
            marshaller.setProperty(Marshaller.JAXB_FRAGMENT, fragment);         // 是否省略xm头声明信息
            StringWriter writer = new StringWriter();
            marshaller.marshal(obj, writer);
            return writer.toString();
        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }

    /**
     * xml转java实体类
     */
    @SuppressWarnings("unchecked")
    public static <T> T fromXML(String xml, Class<T> valueType) {
        try {
            JAXBContext jaxbContext = jaxbContextMap.get(valueType.getName());
            if(jaxbContext == null){
                jaxbContext = JAXBContext.newInstance(valueType);
                jaxbContextMap.put(valueType.getName(), jaxbContext);
            }
            Unmarshaller unmarshaller = jaxbContext.createUnmarshaller();
            return (T) unmarshaller.unmarshal(new StringReader(xml));
        } catch (Exception e) {
            throw new RuntimeException(e.getMessage());
        }
    }