xml rpc with sping beans

最近在处理web services时用到apache xmlrpc，这里简单总结一下。

1.选用xml rpc

web services有很多种实现，这里选用xml rpc的是因为公司各个项目都支持xml rpc的调用，其他的web services实现并非完全支持；xml rpc与平台无关；xml rpc可以保证项目与项目之间的无侵入性。

2.spring bean

由于目前的业务组件都由spring container去管理、增强，所以理想的实现是在xml rpc的server端作为服务的beans都由spring container提供。但是 xml rpc server端的默认实现中，服务beans都由classloader去加载，代码如下：

//org.apache.xmlrpc.server.PropertyHandlerMapping
public void load(ClassLoader pClassLoader, Map pMap) throws XmlRpcException {
        for (Iterator iter = pMap.entrySet().iterator();  iter.hasNext();  ) {
            Map.Entry entry = (Map.Entry) iter.next();
            String key = (String) entry.getKey();
            String value = (String) entry.getValue();
            Class c = newHandlerClass(pClassLoader, value);
            registerPublicMethods(key, c);
        }
}

//org.apache.xmlrpc.metadata.Util
    /**
     * Creates a new instance of <code>pClass</code>.
     */
    public static Object newInstance(Class pClass) throws XmlRpcException {
        try {
            return pClass.newInstance();
        } catch (InstantiationException e) {
            throw new XmlRpcException("Failed to instantiate class " + pClass.getName(), e);
        } catch (IllegalAccessException e) {
            throw new XmlRpcException("Illegal access when instantiating class " + pClass.getName(), e);
        }
    }

 

 这样取得一个bean的实例并不能满足我们的要求，例如我们取的bean不能通过依赖注入得到相关属性；不能通过spring中设置的aop切面做动态的增强…………

有鉴于此，我们有必要自己实现一个xml rpc server的factorybean，并将其交由spring container管理。代码如下：

/**
 * <li>xmlrpc server 工厂</li>
 * 
 * @author yangpeng 2008-8-1 上午09:18:34
 */
public class XmlRpcServletServerFactoryBean extends ApplicationObjectSupport
		implements FactoryBean, InitializingBean {

	private XmlRpcServletServer server;
	/** XmlRpcServletServer的属性集合 */
	private Map<String, String> serverProperties;
	/** 是否在父BeanFactory中寻找xml rpc services */
	private boolean detectServersInAncestorContexts = false;
	private AbstractReflectiveHandlerMapping.AuthenticationHandler authenticationHandler;
	private RequestProcessorFactoryFactory requestProcessorFactoryFactory;
	private TypeConverterFactory typeConverterFactory;
	protected Log log = LogFactory.getLog(XmlRpcServletServerFactoryBean.class);

	public Object getObject() throws Exception {
		return server;
	}
	public Class<?> getObjectType() {
		return XmlRpcServletServer.class;
	}
	public boolean isSingleton() {
		return true;
	}
	public void afterPropertiesSet() throws Exception {
		server = new XmlRpcServletServer();
		initServerProperties();
		server.setHandlerMapping(newXmlRpcHandlerMapping());
	}
	protected void initServerProperties() {
		if (null != serverProperties) {
			Set<String> keys = serverProperties.keySet();
			for (String key : keys) {
				String value = serverProperties.get(key);
				try {
					if (!ReflectionUtil.setProperty(this, key, value)
							&& !ReflectionUtil.setProperty(server, key, value)
							&& !ReflectionUtil.setProperty(server.getConfig(),
									key, value)) {
						throw new BeanInitializationException("key:" + key
								+ ";value:" + value + " is wrong property!");
					}
				}
				catch (IllegalAccessException e) {
					log.error(e);
					throw new BeanInitializationException("key:" + key
							+ ";value:" + value + " is wrong property!");
				}
				catch (InvocationTargetException e) {
					log.error(e);
					throw new BeanInitializationException("key:" + key
							+ ";value:" + value + " is wrong property!");
				}
			}
		}
	}
	protected XmlRpcHandlerMapping newXmlRpcHandlerMapping()
			throws XmlRpcException {
		SpringPropertyHandlerMapping mapping = new SpringPropertyHandlerMapping();
		mapping.setAuthenticationHandler(authenticationHandler);
		if (requestProcessorFactoryFactory != null) {
			mapping
					.setRequestProcessorFactoryFactory(requestProcessorFactoryFactory);
		}
		if (typeConverterFactory != null) {
			mapping.setTypeConverterFactory(typeConverterFactory);
		}
		else {
			mapping.setTypeConverterFactory(server.getTypeConverterFactory());
		}
		mapping.setVoidMethodEnabled(server.getConfig()
				.isEnabledForExtensions());
		mapping.addHandler(detectServersInAncestorContexts,
				getApplicationContext());
		return mapping;
	}
//省略getter、setter
}

 

 SpringPropertyHandlerMapping继承于PropertyHandlerMapping，重载addHandler方法，将ApplicationContext作为参数传入，addHandler中的实现类似于spring2.5 MVC中查找声明@controller的Controller类的实现。为了能获得这样的效果，我们先要定义两个Annotation：

/**
 * <li>xml rpc service 注解</li>
 * 
 * @author yangpeng 2008-8-1 下午03:37:34
 */
@Target( { ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface XmlRpcService {

	/**
	 * value为空则xml rpc service的名称默认使用sping bean的id。否则使用value
	 */
	String value() default "";
	/**
	 * 是否使用方法注解
	 * 
	 * @return false:默认服务组件中的所有公共方法都作为xml rpc的服务方法 <br>
	 *         true:在服务组件
	 */
	boolean useMethodAnnotation() default false;
}

 

/**
 * <li>标注此方法会作为xmlrpc server的响应方法</li>
 * 
 * @author yangpeng 2008-8-1 下午03:33:12
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface XmlRpcMethod {

	String value() default "";
}

 接着来看看SpringPropertyHandlerMapping，在这里它是核型：

/**
 * <li>注册spring bean的HandlerMapping</li>
 * 
 * @author yangpeng 2008-8-1 上午10:42:21
 */
public class SpringPropertyHandlerMapping extends PropertyHandlerMapping {

	public void addHandler(boolean detectServersInAncestorContexts,
			final ApplicationContext context) throws XmlRpcException {
		Assert.notNull(context, "context must not be null!");
		String[] beanNames = (detectServersInAncestorContexts ? BeanFactoryUtils
				.beanNamesForTypeIncludingAncestors(context, Object.class)
				: context.getBeanNamesForType(Object.class));
		for (String beanName : beanNames) {
			registerPublicMethods(beanName, context);
		}
	}
	@SuppressWarnings( { "unchecked", "unchecked" })
	protected void registerPublicMethods(String beanName,
			final ApplicationContext context) throws XmlRpcException {
		Class<?> serviceType = context.getType(beanName);
		XmlRpcService service = AnnotationUtils.findAnnotation(serviceType,
				XmlRpcService.class);
		if (service == null
				&& context instanceof ConfigurableApplicationContext
				&& context.containsBeanDefinition(beanName)) {
			ConfigurableApplicationContext cac = (ConfigurableApplicationContext) context;
			BeanDefinition bd = cac.getBeanFactory().getMergedBeanDefinition(
					beanName);
			if (bd instanceof AbstractBeanDefinition) {
				AbstractBeanDefinition abd = (AbstractBeanDefinition) bd;
				if (abd.hasBeanClass()) {
					Class<?> beanClass = abd.getBeanClass();
					serviceType = beanClass;// 得到被代理对象
					service = AnnotationUtils.findAnnotation(beanClass,
							XmlRpcService.class);
				}
			}
		}
		if (service != null) {
			Map map = new HashMap();
			Method[] methods = serviceType.getMethods();
			for (Method method : methods) {
				if (!isHandlerMethod(service.useMethodAnnotation(), method)) {
					continue;
				}
				String serviceName = StringUtils.isEmpty(service.value()) ? beanName
						: service.value();
				String name = serviceName + "." + method.getName();
				Method[] mArray;
				Method[] oldMArray = (Method[]) map.get(name);
				if (oldMArray == null) {
					mArray = new Method[] { method };
				}
				else {
					mArray = new Method[oldMArray.length + 1];
					System.arraycopy(oldMArray, 0, mArray, 0, oldMArray.length);
					mArray[oldMArray.length] = method;
				}
				map.put(name, mArray);
			}
			for (Iterator iter = map.entrySet().iterator(); iter.hasNext();) {
				Map.Entry entry = (Map.Entry) iter.next();
				String name = (String) entry.getKey();
				Method[] mArray = (Method[]) entry.getValue();
				handlerMap.put(name, newXmlRpcHandler(
						context.getBean(beanName), mArray));
			}
		}
	}
	protected XmlRpcHandler newXmlRpcHandler(final Object bean,
			final Method[] pMethods) throws XmlRpcException {
		String[][] sig = getSignature(pMethods);
		String help = getMethodHelp(bean.getClass(), pMethods);
		if (sig == null || help == null) {
			return new SpringXmlRpcHandler(this, getTypeConverterFactory(),
					bean, pMethods);
		}
		return new SpringReflectiveXmlRpcMetaDataHandler(this,
				getTypeConverterFactory(), bean, pMethods, sig, help);
	}
	protected boolean isHandlerMethod(boolean useMethodAnnotation, Method method) {
		if (useMethodAnnotation) {
			XmlRpcMethod xmlRpcMethod = AnnotationUtils.getAnnotation(method,
					XmlRpcMethod.class);
			if (null == xmlRpcMethod) {
				return false;
			}
		}
		return super.isHandlerMethod(method);
	}
}

 简单解释一下。SpringPropertyHandlerMapping遍历spring container中所有注册的beans，查找使用了@XmlRpcService注解的bean(无论其是否被代理)。对于这样的bean认为提供xml rpc服务，然后查找其声明的xml rpc服务方法。默认情况下，其所有的public、非static、非Object类方法的方法都会被当作xml rpc的服务方法(有点拗口)。如果在XmlRpcService注解中声明useMethodAnnotation为true，则其method除了要满足以上条件外，还要必须声明XmlRpcMethod注解才会被认为是xml rpc的服务方法。

SpringXmlRpcHandler与SpringReflectiveXmlRpcMetaDataHandler都非常简单，类似于默认实现的ReflectiveXmlRpcHandler、ReflectiveXmlRpcMetaDataHandler，这里就不多展开演示了。

3.例子

server1：

使用spring自带的petclinic，为业务实现一个xml rpc的faced：

package org.springframework.samples.petclinic.xmlrpcfaced;

import java.util.Collection;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.samples.petclinic.Clinic;
import org.springframework.samples.petclinic.PetType;

import xmlrpc.annotation.XmlRpcService;

@XmlRpcService
public class PetFaced {

	@Autowired
	Clinic clinic;

	public String getPetTypesName() {
		Collection<PetType> types = clinic.getPetTypes();
		String typesName = "";
		for (PetType petType : types) {
			typesName += petType.getName() + ",";
		}
		return typesName;
	}
}

  springcontext：

	<bean id="rpcServer"
		class="xmlrpc.server.XmlRpcServletServerFactoryBean">
		<property name="serverProperties">
			<map>
				<entry key="enabledForExtensions" value="true"></entry>
			</map>
		</property>
	</bean>

 最后实现一个测试filter：

public class SpringXmlRpcFilter extends OncePerRequestFilter {

	public static final String DEFAULT_XML_RPC_SERVIER_NAME = "xmlRpcServer";
	private String servierName = DEFAULT_XML_RPC_SERVIER_NAME;
	private XmlRpcServletServer server;

	/*
	 * (non-Javadoc)
	 * 
	 * @see org.springframework.web.filter.OncePerRequestFilter#doFilterInternal(javax.servlet.http.HttpServletRequest,
	 *      javax.servlet.http.HttpServletResponse, javax.servlet.FilterChain)
	 */
	@Override
	protected void doFilterInternal(HttpServletRequest request,
			HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {
		server.execute(request, response);
		// filterChain.doFilter(request, response);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.springframework.web.filter.GenericFilterBean#initFilterBean()
	 */
	@Override
	protected void initFilterBean() throws ServletException {
		WebApplicationContext wac = WebApplicationContextUtils
				.getRequiredWebApplicationContext(getServletContext());
		server = (XmlRpcServletServer) wac.getBean(servierName,
				XmlRpcServletServer.class);
	}
	public String getServierName() {
		return servierName;
	}
	public void setServierName(String servierName) {
		this.servierName = servierName;
	}
}

 server2：

使用被spring container代理过的service、具有事务属性的bean作为xml rpc的service

@XmlRpcService(useMethodAnnotation = true)
@Transactional
public class HibernateClinic implements Clinic {
	@Autowired
	private SessionFactory sessionFactory;
	@XmlRpcMethod
	@Transactional(readOnly = true)
	public String getTypeName(int id) throws DataAccessException {
		return String.valueOf(sessionFactory.getCurrentSession().createQuery(
				"select name from PetType type where id = ?").setInteger(0, id)
				.uniqueResult());
	}
//其他方法省略
}

 其他地方都一样，只是省略了faced。

个人总结

xml rpc的明显局限是对于复杂、用户自定义java bean的支持很弱，只支持一些基本的类型。

性能方面我没有做过测试，不能乱讲。

目前3.1的发布版本的客户端代码的默认实现有线程不安全的bug，这个问题在后来的2007年10月份的版本中才被修复，但是提供给大家下载的版本为8月份的版本，一个有问题的版本，大家注意了！

那个filter有个小问题不知道大家发现了没有，就是如果使用filterChain.doFilter(request, response);这句代码程序会报异常，具体原因我没仔细查，建议大家写个servlet做代替，文档中也是用servlet去做的。

后记

补充一个xml rpc client的包装类，使得客户端也可以通过spring容器管理，注入到需要的service中。详见附件。

做一个简单的改进：使用@Resource注解。

public class XmlRpcServletServerFactoryBean implements FactoryBean,
		InitializingBean {

	@Resource
	private ApplicationContext context;
//........
}

取消对ApplicationObjectSupport.java的继承。

强在哪里呢？
不要这样说。。。
能让你有所收获即可。。。