Javax Transformer 在多线程服务中为 null

Question

我正在使用 Javax Transformer class 来使用 xslts 转换 xml。负载较小时一切正常。但是当负载到来时，事情就开始崩溃了。基本上 transformer 表现出奇怪的行为并设置为 null 从而抛出异常。

代码

@Service
public class XmlProcessorUtil {

    private static final ObjectPool<XPath> pool = new GenericObjectPool<XPath>(new 
      XPathPoolFactory());

    public  String transformXmlUsingXsltWithParams(String xsltPath, Document xml, 
          HashMap<String, String> params) {
        Source xslt = new StreamSource(new File(xsltPath));
        Source xmlSource = new DOMSource(xml);
        return transformXmlUsingXsltWithParams(xslt, xmlSource, params);
    }

    public  String transformXmlUsingXsltWithParams(Source xslt, Source xml, HashMap<String, String> params)
    {
        String result = "";
        StringWriter writer = new StringWriter();

        if(xslt == null)
            return null;

        Transformer transformer = null;

        try
        {
            transformer = TransformerFactory.newInstance().newTransformer(xslt);
        }
        catch (Exception e)
        {

            return null;
        }

        if(params != null && !params.isEmpty())
        {
            for(String key : params.keySet())
            {
                if(transformer != null)
                    transformer.setParameter(key, params.get(key));
            }
        }
        try
        {
            if(transformer==null) {
                LOGGER.info("Transformer is null!!");
            }
            if(xml==null) {
                LOGGER.info("XML  is null!!");
            }
            transformer.transform(xml, new StreamResult(writer));
        }
        catch (TransformerException e)
        {
            e.printStackTrace();
            return null;
        }
        result = writer.toString();
        return result;
    }
}

在日志中搜索时，有很多 "Transformer is null!!" 的实例。此外，错误是间歇性的。 class 是一个 bean，用于转换的方法 (transformXmlUsingXsltWithParams) 是一个实例方法，很明显。没有例外设置这个

transformer = TransformerFactory.newInstance().newTransformer(xslt);

但变压器仍然是空的。

PS：此方法被多个线程高度调用，因此我在函数中使用 transformer 作为局部变量

谁能提供解决方法。

编辑：

@Bean 
    TransformerFactory transformerFactory() {
        return TransformerFactory.newInstance();
    }

@Service
public class XmlProcessorUtil {

    private static final ObjectPool<XPath> pool = new GenericObjectPool<XPath>(new XPathPoolFactory());

    public static final org.slf4j.Logger LOGGER = LoggerFactory.getLogger(XmlProcessorUtil.class);

    @Autowired
    TransformerFactory transformerFactory ;

    public  String transformXmlUsingXsltWithParams(String xsltPath, Document xml, HashMap<String, String> params) {
        Source xslt = new StreamSource(new File(xsltPath));
        Source xmlSource = new DOMSource(xml);
        return transformXmlUsingXsltWithParams(xslt, xmlSource, params);
    }

    public  String transformXmlUsingXsltWithParams(Source xslt, Source xml, HashMap<String, String> params)
    {
        String result = "";
        StringWriter writer = new StringWriter();

        if(xslt == null)
            return null;

        Transformer transformer = null;

        try
        {
            transformer = transformerFactory.newTemplates(xslt).newTransformer();
        }
        catch (Exception e)
        {
            LOGGER.warn("Error in setting transformer",e);
            return null;
        }

        if(params != null && !params.isEmpty())
        {
            for(String key : params.keySet())
            {
                if(transformer != null)
                    transformer.setParameter(key, params.get(key));
            }
        }
        try
        {
            if(transformer==null) {
                LOGGER.info("Transformer is null!!");
            }
            if(xml==null) {
                LOGGER.info("XML  is null!!");
            }
            transformer.transform(xml, new StreamResult(writer));
        }
        catch (TransformerException e)
        {
            e.printStackTrace();
            return null;
        }
        result = writer.toString();
        return result;
    }
}

Answer 1

不完全清楚这里发生了什么，但是您在多线程环境中使用 JAXP 看起来完全不对。

您应该尝试为整个应用程序创建一个 TransformerFactory 实例。您应该为每个样式表创建一个 Templates 对象，如果同一个样式表要用于多个转换则将其缓存。并且您应该为每个转换创建一个 Transformer（使用 Templates.newTransformer()），注意 Transformer 只能在单个线程中使用。

Javax Transformer 在多线程服务中为 null

Javax Transformer is null in mutli threaded service

java

xslt

spring

javabeans

spring-boot