項目選定Hessian作為web service的實現方式，確實很輕量級，速度就跟直接用socket差不多，全是二進制傳送節約了不少開銷。但是在使用過程中有業務需要是必須獲得遠程端的ip地址，主機名等信息的。翻便Hessian的文檔和google了n次未果，迫不得已到caucho和spring論壇去問，都沒有得到答復。今天心一橫把hessian的源代碼加入到項目中單步跟蹤，總算有點小收獲。獻丑分享出來，一方面給需要的朋友，主要還是希望各位找找是否存在bug，以及是否有更好的改良。
一：先撇開Spring不談，來看看純Hessian的調用
按照hessian文檔裡邊介紹的demo，在web.xml裡邊如下配置
Java代碼
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.caucho.hessian.server.HessianServlet</servlet-class>
<init-param>
<param-name>home-class</param-name>
<param-value>example.BasicService</param-value>
</init-param>
<init-param>
<param-name>home-api</param-name>
<param-value>example.Basic</param-value>
</init-param>
</servlet>
<servlet-mapping>
<url-pattern>/hello</url-pattern>
<servlet-name>hello</servlet-name>
</servlet-mapping>
由此可知Hessian調用的入口是HessianServlet這個Servlet，進去看看
Java代碼
/**
* Servlet for serving Hessian services.
*/
public class HessianServlet extends GenericServlet {
private Class _homeAPI;
private Object _homeImpl;
private Class _objectAPI;
private Object _objectImpl;
private HessianSkeleton _homeSkeleton;
private HessianSkeleton _objectSkeleton;
private SerializerFactory _serializerFactory;
public String getServletInfo()
{
return "Hessian Servlet";
}
/**
* Sets the home api.
*/
public void setHomeAPI(Class api)
{
_homeAPI = api;
}
/**
* Sets the home implementation
*/
public void setHome(Object home)
{
_homeImpl = home;
}
/**
* Sets the object api.
*/
public void setObjectAPI(Class api)
{
_objectAPI = api;
}
/**
* Sets the object implementation
*/
public void setObject(Object object)
{
_objectImpl = object;
}
/**
* Sets the service class.
*/
public void setService(Object service)
{
setHome(service);
}
/**
* Sets the api-class.
*/
public void setAPIClass(Class api)
{
setHomeAPI(api);
}
/**
* Gets the api-class.
*/
public Class getAPIClass()
{
return _homeAPI;
}
/**
* Sets the serializer factory.
*/
public void setSerializerFactory(SerializerFactory factory)
{
_serializerFactory = factory;
}
/**
* Gets the serializer factory.
*/
public SerializerFactory getSerializerFactory()
{
if (_serializerFactory == null)
_serializerFactory = new SerializerFactory();
return _serializerFactory;
}
/**
* Sets the serializer send collection java type.
*/
public void setSendCollectionType(boolean sendType)
{
getSerializerFactory().setSendCollectionType(sendType);
}
/**
* Initialize the service, including the service object.
*/
public void init(ServletConfig config)
throws ServletException
{
super.init(config);
try {
if (_homeImpl != null) {
}
else if (getInitParameter("home-class") != null) {
String className = getInitParameter("home-class");
Class homeClass = loadClass(className);
_homeImpl = homeClass.newInstance();
init(_homeImpl);
}
else if (getInitParameter("service-class") != null) {
String className = getInitParameter("service-class");
Class homeClass = loadClass(className);
_homeImpl = homeClass.newInstance();
init(_homeImpl);
}
else {
if (getClass().equals(HessianServlet.class))
throw new ServletException("server must extend HessianServlet");
_homeImpl = this;
}
if (_homeAPI != null) {
}
else if (getInitParameter("home-api") != null) {
String className = getInitParameter("home-api");
_homeAPI = loadClass(className);
}
else if (getInitParameter("api-class") != null) {
String className = getInitParameter("api-class");
_homeAPI = loadClass(className);
}
else if (_homeImpl != null) {
_homeAPI = findRemoteAPI(_homeImpl.getClass());
if (_homeAPI == null)
_homeAPI = _homeImpl.getClass();
}
if (_objectImpl != null) {
}
else if (getInitParameter("object-class") != null) {
String className = getInitParameter("object-class");
Class objectClass = loadClass(className);
_objectImpl = objectClass.newInstance();
init(_objectImpl);
}
if (_objectAPI != null) {
}
else if (getInitParameter("object-api") != null) {
String className = getInitParameter("object-api");
_objectAPI = loadClass(className);
}
else if (_objectImpl != null)
_objectAPI = _objectImpl.getClass();
_homeSkeleton = new HessianSkeleton(_homeImpl, _homeAPI);
if (_objectAPI != null)
_homeSkeleton.setObjectClass(_objectAPI);
if (_objectImpl != null) {
_objectSkeleton = new HessianSkeleton(_objectImpl, _objectAPI);
_objectSkeleton.setHomeClass(_homeAPI);
}
else
_objectSkeleton = _homeSkeleton;
} catch (ServletException e) {
throw e;
} catch (Exception e) {
throw new ServletException(e);
}
}
private Class findRemoteAPI(Class implClass)
{
if (implClass == null || implClass.equals(GenericService.class))
return null;
Class []interfaces = implClass.getInterfaces();
if (interfaces.length == 1)
return interfaces[0];
return findRemoteAPI(implClass.getSuperclass());
}
private Class loadClass(String className)
throws ClassNotFoundException
{
ClassLoader loader = Thread.currentThread().getContextClassLoader();
if (loader != null)
return Class.forName(className, false, loader);
else
return Class.forName(className);
}
private void init(Object service)
throws ServletException
{
if (service instanceof Service)
((Service) service).init(getServletConfig());
else if (service instanceof Servlet)
((Servlet) service).init(getServletConfig());
}
/**
* Execute a request. The path-info of the request selects the bean.
* Once the bean's selected, it will be applied.
*/
public void service(ServletRequest request, ServletResponse response)
throws IOException, ServletException
{
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
if (! req.getMethod().equals("POST")) {
res.setStatus(500, "Hessian Requires POST");
PrintWriter out = res.getWriter();
res.setContentType("text/html");
out.println("<h1>Hessian Requires POST</h1>");
return;
}
String serviceId = req.getPathInfo();
String objectId = req.getParameter("id");
if (objectId == null)
objectId = req.getParameter("ejbid");
ServiceContext.begin(req, serviceId, objectId);
try {
InputStream is = request.getInputStream();
OutputStream os = response.getOutputStream();
Hessian2Input in = new Hessian2Input(is);
AbstractHessianOutput out;
SerializerFactory serializerFactory = getSerializerFactory();
in.setSerializerFactory(serializerFactory);
int code = in.read();
if (code != 'c') {
// XXX: deflate
throw new IOException("expected 'c' in hessian input at " + code);
}
int major = in.read();
int minor = in.read();
if (major >= 2)
out = new Hessian2Output(os);
else
out = new HessianOutput(os);
out.setSerializerFactory(serializerFactory);
if (objectId != null)
_objectSkeleton.invoke(in, out);
else
_homeSkeleton.invoke(in, out);
out.close();
} catch (RuntimeException e) {
throw e;
} catch (ServletException e) {
throw e;
} catch (Throwable e) {
throw new ServletException(e);
} finally {
ServiceContext.end();
}
}
}
先看init()函數，功能還是一樣，初始話一些東西，讀入init-param的內容，並且load這些init-param的class
主要的還是service()函數
在service函數裡邊會獲得request和response對象的輸入和輸出流，用來構造Hessian2Input和Hessian2Output，Hessian就是解析這兩個東西來執行函數調用的。當然，在service裡邊還有一個重要的語句
Java代碼
ServiceContext.begin(req, serviceId, objectId);
這個函數有點奇怪，我每次到這裡serviceId和objectId都是空，不知道是不是歷史遺留問題還存在這兩個參數。
進去這個類看看
Java代碼
public class ServiceContext {
private static final ThreadLocal _localContext = new ThreadLocal();
private ServletRequest _request;
private String _serviceName;
private String _objectId;
private int _count;
private HashMap _headers = new HashMap();
private ServiceContext()
{
}
/**
* Sets the request object prior to calling the service's method.
*
* @param request the calling servlet request
* @param serviceId the service identifier
* @param objectId the object identifier
*/
public static void begin(ServletRequest request,
String serviceName,
String objectId)
throws ServletException
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context == null) {
context = new ServiceContext();
_localContext.set(context);
}
context._request = request;
context._serviceName = serviceName;
context._objectId = objectId;
context._count++;
}
/**
* Returns the service request.
*/
public static ServiceContext getContext()
{
return (ServiceContext) _localContext.get();
}
/**
* Adds a header.
*/
public void addHeader(String header, Object value)
{
_headers.put(header, value);
}
/**
* Gets a header.
*/
public Object getHeader(String header)
{
return _headers.get(header);
}
/**
* Gets a header from the context.
*/
public static Object getContextHeader(String header)
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context != null)
return context.getHeader(header);
else
return null;
}
/**
* Returns the service request.
*/
public static ServletRequest getContextRequest()
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context != null)
return context._request;
else
return null;
}
/**
* Returns the service id, corresponding to the pathInfo of the URL.
*/
public static String getContextServiceName()
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context != null)
return context._serviceName;
else
return null;
}
/**
* Returns the object id, corresponding to the ?id= of the URL.
*/
public static String getContextObjectId()
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context != null)
return context._objectId;
else
return null;
}
/**
* Cleanup at the end of a request.
*/
public static void end()
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context != null && --context._count == 0) {
context._request = null;
context._headers.clear();
}
}
/**
* Returns the service request.
*
* @deprecated
*/
public static ServletRequest getRequest()
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context != null)
return context._request;
else
return null;
}
/**
* Returns the service id, corresponding to the pathInfo of the URL.
*
* @deprecated
*/
public static String getServiceName()
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context != null)
return context._serviceName;
else
return null;
}
/**
* Returns the object id, corresponding to the ?id= of the URL.
*
* @deprecated
*/
public static String getObjectId()
{
ServiceContext context = (ServiceContext) _localContext.get();
if (context != null)
return context._objectId;
else
return null;
}
}
原來ServiceContext 是用來保存當前調用線程的上下文的，比如request對象等（不知道這個解釋對不對）。有了這個東西就太好了，因為裡邊有request，就有了調用端的一切信息，呵呵。
繼續回來看那個Servlet，到了真正調用的時候了，也就是這段代碼
Java代碼
if (objectId != null)
_objectSkeleton.invoke(in, out);
else
_homeSkeleton.invoke(in, out);
跟蹤invoke方法看看真面目
Java代碼
public void invoke(AbstractHessianInput in, AbstractHessianOutput out)
throws Throwable
{
ServiceContext context = ServiceContext.getContext();
String header;
while ((header = in.readHeader()) != null) {
Object value = in.readObject();
context.addHeader(header, value);
}
String ip = context.getContextRequest().getRemoteAddr();
String methodName = in.readMethod();
Method method = getMethod(methodName);
if (method != null) {
}
else if ("_hessian_getAttribute".equals(methodName)) {
String attrName = in.readString();
in.completeCall();
String value = null;
if ("java.api.class".equals(attrName))
value = getAPIClassName();
else if ("java.home.class".equals(attrName))
value = getHomeClassName();
else if ("java.object.class".equals(attrName))
value = getObjectClassName();
out.startReply();
out.writeObject(value);
out.completeReply();
return;
}
else if (method == null) {
out.startReply();
out.writeFault("NoSuchMethodException",
"The service has no method named: " + in.getMethod(),
null);
out.completeReply();
return;
}
Class []args = method.getParameterTypes();
Object []values = new Object[args.length];
//args[0]
for (int i = 0; i < args.length; i++){
if(i == args.length-1){
values[i] = in.readObject(args[i], ip);
}else{
values[i] = in.readObject(args[i]);
}
}
in.completeCall();
Object result = null;
try {
result = method.invoke(_service, values);
} catch (Throwable e) {
if (e instanceof InvocationTargetException)
e = ((InvocationTargetException) e).getTargetException();
log.log(Level.WARNING, e.toString(), e);
out.startReply();
out.writeFault("ServiceException", e.getMessage(), e);
out.completeReply();
return;
}
out.startReply();
out.writeObject(result);
out.completeReply();
}
就是在這個方法裡邊，hessian把包裝過的輸入輸出流當作參數傳入並進行解析的，看看這個函數的第一句，正是取得ServiceContext的地方，此時應該就是把剛才Servlet裡邊保存的上下文取出來使用。
這個時候出現了第一個hack的地方
Java代碼
String ip = context.getContextRequest().getRemoteAddr();
在此處我取得遠程的ip地址保存起來。然後在第二個hack的地方
Java代碼
Class []args = method.getParameterTypes();
Object []values = new Object[args.length];
//args[0]
for (int i = 0; i < args.length; i++){
if(i == args.length-1){
values[i] = in.readObject(args[i], ip);
}else{
values[i] = in.readObject(args[i]);
}
}
我用這個ip地址取代最後一個參數（web服務函數的參數，即遠程端調用的函數的參數）。
第三個hack的地方就是 in.readObject(args[i], ip); 這個方法。 這個方法是我自己加的，原本只有
in.readObject(args[i]); 這個方法。 這個方法就是hessian讀取參數值的地方
進去看看
Java代碼
/**
* Reads an object from the input stream with an expected type.
*/
public Object readObject(Class cl, String ip)
throws IOException
{
if (cl == null || cl == Object.class)
return readObject();
int tag = _offset < _length ? (_buffer[_offset++] & 0xff) : read();
switch (tag) {
case 'N':
return null;
case 'M':
{
String type = readType();
Deserializer reader;
reader = findSerializerFactory().getObjectDeserializer(type);
if (cl != reader.getType() && cl.isAssignableFrom(reader.getType()))
return reader.readMap(this);
reader = findSerializerFactory().getDeserializer(cl);
return reader.readMap(this);
}
case 'O':
{
return readObjectDefinition(cl);
}
case 'o':
{
int ref = readInt();
ObjectDefinition def = (ObjectDefinition) _classDefs.get(ref - 1);
return readObjectInstance(cl, def);
}
case 'V':
{
String type = readType();
int length = readLength();
Deserializer reader;
reader = findSerializerFactory().getObjectDeserializer(type);
if (cl != reader.getType() && cl.isAssignableFrom(reader.getType()))
return reader.readList(this, length);
reader = findSerializerFactory().getDeserializer(cl);
Object v = reader.readList(this, length);
return v;
}
case 'v':
{
int ref = readInt();
String type = (String) _types.get(ref);
int length = readInt();
Deserializer reader;
reader = findSerializerFactory().getObjectDeserializer(type);
if (cl != reader.getType() && cl.isAssignableFrom(reader.getType()))
return reader.readLengthList(this, length);
reader = findSerializerFactory().getDeserializer(cl);
Object v = reader.readLengthList(this, length);
return v;
}
case 'R':
{
int ref = parseInt();
return _refs.get(ref);
}
case 'r':
{
String type = readType();
String url = readString();
return resolveRemote(type, url);
}
}
if (tag >= 0)
_offset--;
Object value = findSerializerFactory().getDeserializer(cl).readObject(this);
if(value instanceof String){
value = ip;
}
return value;
}
我重載了這個方法，加入了一個String類型的參數，用來把ip地址傳進去，並且最後返回這個值。到了這裡，hack的原理大家應該知道了--就是強行修改遠程調用端的調用函數裡邊的最後一個參數的值（規定為String類型），把這個值設為我想要的信息，那麼服務端的服務函數就會獲得這個值，並且進行後續處理。
剩下的步驟就原封不動的是hessian來處理了，沒有需要干涉的地方，你也就能在你的服務端service函數裡邊獲得這個你想要的信息了。
這就是Hessian的一個普通流程，不知道分析和Hack的對不對，我在這裡是調試成功了，但是還沒徹底測試有沒有其它bug。 至於跟Spring的結合，待會兒跟帖來說。
