java – 如何在返回多种类型的XML的URL上使用Spring RestTemplate和JAXB编组

我需要对一个返回“< job />或者< exception />并始终处于状态码200.(跛脚第三方产品！).

我有如下代码：

Job job = getRestTemplate().postForObject(url,postData,Job.class);

我的applicationContext.xml看起来像：

<bean id="restTemplate" class="org.springframework.web.client.RestTemplate">
    <constructor-arg ref="httpClientFactory"/>

    <property name="messageConverters">
        <list>
            <bean class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">
                <property name="marshaller" ref="jaxbMarshaller"/>
                <property name="unmarshaller" ref="jaxbMarshaller"/>
            </bean>
            <bean class="org.springframework.http.converter.FormHttpMessageConverter"/>
            <bean class="org.springframework.http.converter.StringHttpMessageConverter"/>
        </list>
    </property>
</bean>

<bean id="jaxbMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
    <property name="classesToBeBound">
        <list>
            <value>domain.fullspec.Job</value>
            <value>domain.fullspec.Exception</value>
        </list>
    </property>
</bean>

当我尝试使这个电话和服务失败,我得到：

Failed to convert value of type 'domain.fullspec.Exception' to required type 'domain.fullspec.Job'

在postForObject()调用中,我要求一个Job.class,而不是得到一个,它正在变得不安.

我想我需要能够做的事情是：

Object o = getRestTemplate().postForObject(url,Object.class);
if (o instanceof Job.class) {
   ...
else if (o instanceof Exception.class) {
}

但是这不行,因为JAXB抱怨说它不知道如何组织到Object.class – 并不奇怪.

我试图创建MarshallingHttpMessageConverter的子类并重写readFromSource()

protected Object readFromSource(类clazz,HttpHeaders头,源代码){

Object o = null;
    try {
        o = super.readFromSource(clazz,headers,source);
    } catch (Exception e) {
        try {
            o = super.readFromSource(MyCustomException.class,source);
        } catch (IOException e1) {
            log.info("Failed readFromSource "+e);
        }
    }

    return o;
}

不幸的是,这不工作,因为在我重试之前,源代码中的底层输入流已被关闭.

有意见的建议,

汤姆

更新：我已经通过获取一个inputStream的副本来工作

protected Object readFromSource(Class<?> clazz,HttpHeaders headers,Source source) {
    InputStream is = ((StreamSource) source).getInputStream();

    // Take a copy of the input stream so we can use it for initial JAXB conversion
    // and if that fails,we can try to convert to Exception
    CopyInputStream copyInputStream = new CopyInputStream(is);

    // input stream in source is empty now,so reset using copy
    ((StreamSource) source).setInputStream(copyInputStream.getCopy());

    Object o = null;
    try {
        o = super.readFromSource(clazz,source);
      // we have failed to unmarshal to 'clazz' - assume it is <exception> and unmarshal to MyCustomException

    } catch (Exception e) {
        try {

            // reset input stream using copy
            ((StreamSource) source).setInputStream(copyInputStream.getCopy());
            o = super.readFromSource(MyCustomException.class,source);

        } catch (IOException e1) {
            e1.printStackTrace();  
        }
        e.printStackTrace();
    }
    return o;

}

CopyInputStream取自http://www.velocityreviews.com/forums/t143479-how-to-make-a-copy-of-inputstream-object.html,我将其粘贴到这里.

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;

public class CopyInputStream
{
private InputStream _is;
private ByteArrayOutputStream _copy = new ByteArrayOutputStream();

/**
 * 
 */
public CopyInputStream(InputStream is)
{
    _is = is;

    try
    {
        copy();
    }
    catch(IOException ex)
    {
        // do nothing
    }
}

private int copy() throws IOException
{
    int read = 0;
    int chunk = 0;
    byte[] data = new byte[256];

    while(-1 != (chunk = _is.read(data)))
    {
        read += data.length;
        _copy.write(data,chunk);
    }

    return read;
}

public InputStream getCopy()
{
    return (InputStream)new ByteArrayInputStream(_copy.toByteArray());
}
}

解决方法

我读了RestTemplate source code,你目前正在调用这个API：

public <T> T postForObject(URI url,Object request,Class<T> responseType) throws RestClientException {
    HttpEntityRequestCallback requestCallback = new HttpEntityRequestCallback(request,responseType);
    HttpMessageConverterExtractor<T> responseExtractor =
            new HttpMessageConverterExtractor<T>(responseType,getMessageConverters());
    return execute(url,HttpMethod.POST,requestCallback,responseExtractor);
}

您可以看到,它会根据您的响应类型返回类型T.您可能需要做的是对RestTemplate进行子类化,并添加一个返回Object而不是类型T的新的PostForObject()API,以便您可以对返回的对象执行instanceof检查.

UPDATE

我一直在想这个问题的解决方案,而不是使用内置的RestTemplate,为什么不自己写？我认为比子类RestTemplate更好的添加一个新的方法.

这是我的例子…授予,我没有测试这个代码,但它应该给你一个想法：

// reuse the same marshaller wired in RestTemplate
@Autowired
private Jaxb2Marshaller jaxb2Marshaller;

public Object genericPost(String url) {
    // using Commons HttpClient
    HttpClient client = new HttpClient();
    PostMethod method = new PostMethod(url);

    // add your data here
    method.addParameter("data","your-data");

    try {
        int returnCode = client.executeMethod(method);

        // status code is 200
        if (returnCode == HttpStatus.SC_OK) {
            // using Commons IO to convert inputstream to string
            String xml = IOUtil.toString(method.getResponseBodyAsStream());
            return jaxb2Marshaller.unmarshal(new StreamSource(new ByteArrayInputStream(xml.getBytes("UTF-8"))));
        }
        else {
            // handle error
        }
    }
    catch (Exception e) {
        throw new RuntimeException(e);
    }
    finally {
        method.releaseConnection();
    }

    return null;
}

如果有些情况需要重新使用RestTemplate中的一些API,那么您可以构建一个适配器来封装您的自定义实现并重用RestTemplate API,而不会在您的代码中实际暴露RestTemplate API.

例如,您可以创建一个适配器接口,如下所示：

public interface MyRestTemplateAdapter {
    Object genericPost(String url);

    // same signature from RestTemplate that you want to reuse
    <T> T postForObject(String url,Class<T> responseType,Object... uriVariables);
}

具体的定制休息模板看起来像这样：

public class MyRestTemplateAdapterImpl implements MyRestTemplateAdapter {
    @Autowired
    private RestTemplate    restTemplate;

    @Autowired
    private Jaxb2Marshaller jaxb2Marshaller;

    public Object genericPost(String url) {
        // code from above
    }

    public <T> T postForObject(String url,Object... uriVariables) {
        return restTemplate.postForObject(url,request,responseType);
    }
}

我仍然认为这种方法比使用RestTemplate的子类更清晰,您可以更好地控制如何处理Web服务调用的结果.

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