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Hessian，轻量级的Java Remoting方案
摘要: Hessian，轻量级的Java Remoting方案
项目里遇到一个问题：由于安全性的需要，必须由一个程序专门负责查询某一数据
库，然后通过安全的信道（例如HTTP）将查询结果传到安全区域之外的application
。为了解决这个小小的remoting问题，我们差点要动用EJB。不过幸亏朋友推荐，找
到了Hessian这个轻量级的remoting on http工具。
Hessian其实很像web service，只不过它的协议不是SOAP，而是它自己规定的
binary协议。Hessian的server端提供一个servlet基类，client端获得一个service
接口（也就是stub）之后调用上面的方法，stub将方法调用marshal之后通过HTTP传
到server，server借助reflection调用service方法。
简单、轻量。对付普通的remoting问题，Hessian足够了。我们又可以暂时忘掉EJB和RMI了。 ——————————
Hessian is a simple binary protocol for connecting web services. The
com.caucho.hessian.client and com.caucho.hessian.server packages do not
require any other Resin classes, so can be used in smaller clients, like
applets.
Because Hessian is a small protocol, J2ME devices like cell-phones can
use it to connect to Resin servers. Because it's powerful, it can be used
for EJB services.
The Hessian home page contains the latest information about Hessian
including the Hessian specification .
Hessian Client
Hessian Service
Hessian Client for a cell-phone
Hessian Serialization
Hessian Client
Using a Hessian service from a Java client is like calling a method. The
HessianProxyFactory creates proxies which act like normal Java objects,
with possibility that the method might throw a protocol exception if the
remote connection fails. Using HessianProxyFactory requires JDK 1.3.
Each service will have a normal Java interface describing the service.
The trivial hello, world example just returns a string. Because the
Hessian services support Java serialization, any Java type can be used.
API for Basic service package hessian.test;
public interface Basic {
public String hello(); }
The following is an example of a standalone Hessian client. The client
creates a HessianProxyFactory. The client uses the factory to create
client stubs with the given target URL and a Java interface for the API. The returned object is a stub implementing the API.
Hessian Client for Basic service package hessian.test;
import com.caucho.hessian.client.HessianProxyFactory;
public class BasicClient {
public static void main(String []args)
throws Exception {
String url = "http://www.caucho.com/hessian/test/basic";
HessianProxyFactory factory = new HessianProxyFactory();
Basic basic = (Basic) factory.create(Basic.class, url);
System.out.println("Hello: " + basic.hello()); } }
That's it! There are no more complications to using the client. The
service can add methods and use any Java type for parameters and results.
Hessian Service
While most Hessian services will use Resin-CMP or Resin-EJB, to take
advantage of the benefits of EJB, the Hessian library makes it possible
to write services by extending HessianServlet.
Any public method is treated as a service method. So adding new methods is as easy as writing a normal Java class.
Because the service is implemented as a Servlet, it can use all the
familiar servlet data in the ServletContext, just like a normal servlet.
Hello Service package hessian.test;
import com.caucho.hessian.server.HessianServlet;
public class BasicService extends HessianServlet implements Basic {
public String hello() {
return "Hello, world"; } }
Hessian Client for a cell-phone
Hessian can be used for even small Java devices. The following classes
from com.caucho.hessian.client can be extracted into a J2ME jar:
MicroHessianInput
MicroHessianOutput
HessianRemote
HessianServiceException
HessianProtocolException
The following example shows the code for using a cell phone as a client.
It's a bit more complicated than using the proxy, since the client is
responsible for creating the connection and writing the data.
Hello, world import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection; ...
MicroHessianInput in = new MicroHessianInput();
String url = "http://www.caucho.com/hessian/test/basic";
HttpConnection c = (HttpConnection) Connector.open(url);
c.setRequestMethod(HttpConnection.POST);
OutputStream os = c.openOutputStream();
MicroHessianOutput out = new MicroHessianOutput(os);
out.call("hello", null);
os.flush();
is = c.openInputStream();
MicroHessianInput in = new MicroHessianInput(is);
Object value = in.readReply(null);
Hessian Serialization
The Hessian classes can be used for serialization and deserialization.
Serialization Object obj = ...;
OutputStream os = new FileOutputStream("test.xml");
HessianOutput out = new HessianOutput(os);
out.writeObject(obj);
os.close();
Deserialization InputStream is = new FileInputStream("test.xml");
HessianInput in = new HessianInput(is);
Object obj = in.readObject(null);
is.close();
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对该文的评论 人气：1067
item001(2003-12-13 17:06:20)
不过，如果系统要扩展，还是要改用JMS或者EJB
coollzh(2003-12-13 12:35:53)
goooooooooooood
gigix(2003-12-12 19:30:16)
没错，RMI提供IIOP的支持。
但RMI的问题在于稍微复杂了一点。你要自己去开一个server，还要占用一个port来
监听。Hessian的好处就在于简单——它就是一个servlet，随便附在哪个
application server上，就可以从80端口监听请求。
ys19811110(2003-12-12 17:47:28)
我不是做java的，但是我觉得好像rmi支持binary的传输方式，不知道是不是这样
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