如何简化这种解析方法？

Question

我正在编写代码以从文件中解组 XML。我事先不知道 XML 基于哪个模式，所以我尝试使用不同 Jaxb2Marshaller 实例形式的多个模式来解组它。

该方法需要：

1. 尝试使用每个编组器解组 XML

2. 如果成功，则返回结果对象

3. 如果失败，请尝试下一个 marshaller

4. 如果所有编组器都失败，则抛出带有最后一条错误消息的异常

这是当前代码：

private Object getObject(final byte[] data) throws MyException {

    String lastErrorMessage = "";

    for (final Jaxb2Marshaller marshaller : this.marshallers) {

        try {

            return marshaller.unmarshal(new StreamSource(new ByteArrayInputStream(data)));

        } catch (final XmlMappingException e) {

            LOGGER.warn("Invalid XML", e);

            lastErrorMessage = e.getMessage();

        }

    }

    throw new MyException(lastErrorMessage);

}

我觉得这种方法在不同的抽象层次上做了太多的事情：

• 迭代编组器

• 应用编组器

• 返回结果

• 捕捉异常

• 抛出异常

但我看不到简化它的方法。每个编组器都需要 try-catch 块（因为除了最后一个之外，我应该捕获并忽略这些 XmlMappingExceptions）。该块要么返回一个结果对象，要么返回 lastErrorMessage，在迭代下面需要它来抛出 MyException。

我能想到的唯一解决方案是创建一些人为的 Result 类，其中包含结果对象或错误消息，但感觉很笨拙。还有其他见解吗？

Answer 1

这个怎么样？public class MultiUnmarshaller {&nbsp; &nbsp; private final List<Jaxb2Marshaller> marshallers;&nbsp; &nbsp; private Object value;&nbsp; &nbsp; private String error;&nbsp; &nbsp; public MultiUnmarshaller(List<Jaxb2Marshaller> marshallers) {&nbsp; &nbsp; &nbsp; &nbsp; this.marshallers = marshallers;&nbsp; &nbsp; }&nbsp; &nbsp; private void init() {&nbsp; &nbsp; &nbsp; &nbsp; error = "No marshallers available";&nbsp; &nbsp; &nbsp; &nbsp; value = null;&nbsp; &nbsp; }&nbsp; &nbsp; public Object getObject(byte[] data) throws MyException {&nbsp; &nbsp; &nbsp; &nbsp; init();&nbsp; &nbsp; &nbsp; &nbsp; Iterator<Jaxb2Marshaller> it = marshallers.iterator();&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp; &nbsp; &nbsp; &nbsp; while(it.hasNext() && errorMessage != null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; unmarshalObject(marshaller, data);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; return produceResult();&nbsp; &nbsp; }&nbsp; &nbsp; private void unmarshalObject(Jaxb2Marshaller marshaller, byte[] data) {&nbsp; &nbsp; &nbsp; &nbsp; try {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; value = marshaller.unmarshal(new StreamSource(new&nbsp; &nbsp; &nbsp;ByteArrayInputStream(data)));&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error = null;&nbsp; &nbsp; &nbsp; &nbsp; } catch (final XmlMappingException e) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; LOGGER.warn("Invalid XML", e);&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; error = e.getMessage();&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }&nbsp; &nbsp; private Object produceResult() {&nbsp; &nbsp; &nbsp; &nbsp; if (error == null) {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; return value;&nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; &nbsp; &nbsp; else {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; throw new MyException(error);&nbsp; &nbsp; &nbsp; &nbsp; }&nbsp; &nbsp; }&nbsp; &nbsp;&nbsp;}

Answer 2

我想要具有如下粒度的方法：private Object getObject(byte[] data) throws MyException {&nbsp; &nbsp; Result result;&nbsp; &nbsp; for (Jaxb2Marshaller marshaller : this.marshallers) {&nbsp; &nbsp; &nbsp; &nbsp; result = getObject(marshaller, data);&nbsp; &nbsp; }&nbsp; &nbsp; return handleError(result);}private Result getObject(Jaxb2Marshaller marshaller, byte[] data) {&nbsp; &nbsp; try {&nbsp; &nbsp; &nbsp; &nbsp; return Result.value(marshaller.unmarshal(new StreamSource(new ByteArrayInputStream(data))));&nbsp; &nbsp; } catch (final XmlMappingException e) {&nbsp; &nbsp; &nbsp; &nbsp; LOGGER.warn("Invalid XML", e);&nbsp; &nbsp; &nbsp; &nbsp; return Result.error(e.getMessage());&nbsp; &nbsp; }}private Object handleError(Result result) {&nbsp; &nbsp; if (result.isError()) {&nbsp; &nbsp; &nbsp; &nbsp; throw new MyException(result.errroMessage);&nbsp; &nbsp; }&nbsp; &nbsp; else {&nbsp; &nbsp; &nbsp; &nbsp; return result.value;&nbsp; &nbsp; &nbsp; &nbsp;&nbsp;&nbsp; &nbsp; }}但是附加的 Result 类是冗长而笨拙的：private class Result {&nbsp; &nbsp; String errorMessage;&nbsp; &nbsp; Object value;&nbsp; &nbsp; static Result error(String errorMessage) {&nbsp; &nbsp; &nbsp; &nbsp; Result result = new Result();&nbsp; &nbsp; &nbsp; &nbsp; result.errorMessage = errorMessage;&nbsp; &nbsp; &nbsp; &nbsp; return result;&nbsp; &nbsp; }&nbsp; &nbsp; static Result value(Object value) {&nbsp; &nbsp; &nbsp; &nbsp; Result result = new Result();&nbsp; &nbsp; &nbsp; &nbsp; result.value = value;&nbsp; &nbsp; &nbsp; &nbsp; return result;&nbsp; &nbsp; }&nbsp; &nbsp; boolean isError() {&nbsp; &nbsp; &nbsp; &nbsp; return errorMessage != null;&nbsp; &nbsp; }}