Hessian是 一个轻量级的remoting on http工具,采用的是Binary RPC协议，所以它很适合于发送二进制数据,同时又具有防火墙穿透能力。Hessian一般是通过Web应用来提供服务，因此非常类似于平时我们用的 WebService。只是它不使用SOAP协议,但相比webservice而言更简单、快捷。
Hessian官网：http://hessian.caucho.com/
Hessian可 通过Servlet提供远程服务，需要将匹配某个模式的请求映射到Hessian服务。也可Spring框架整合，通过它的 DispatcherServlet可以完成该功能，DispatcherServlet可将匹配模式的请求转发到Hessian服务。Hessian的 server端提供一个servlet基类, 用来处理发送的请求，而Hessian的这个远程过程调用，完全使用动态代理来实现的,，建议采用面向接口编程，Hessian服务通过接口暴露。
Hessian处理过程示意图：
客户端——>序列化写到输出流——>远程方法(服务器端)——>序列化写到输出流 ——>客户端读取输入流——>输出结果
下面详细介绍最常用的两种方式实现Hessian提供webservice：
纯Hessian实现
配合Spring框架实现
在开始之前当然需要到官网上下载相关的lib包，放入项目的/WEB-INF/lib/下
【一】、纯Hessian实现步骤：
1.基本代码
首先编写一个服务的接口类：HelloHessian.java
Java代码
1. package michael.hessian;
2. import java.util.List;
3. import java.util.Map;
4.
5. /**
6. * @author michael
7. *
8. */
9. public interface HelloHessian {
10.
11. String sayHello();
12.
13. MyCar getMyCar();
14.
15. List myLoveFruit();
16.
17. Map<STRING,&NBSP;STRING> myBabays();
18.
19. }
一个java bean文件MyCar.java:
Java代码
1. package michael.hessian;
2.
3. import java.io.Serializable;
4.
5. /**
6. * @author michael
7. *
8. */
9. public class MyCar implements Serializable {
10.
11. /**
12. *
13. */
14. private static final long serialVersionUID = 4736905401908455439L;
15.
16. private String carName;
17.
18. private String carModel;
19.
20. /**
21. * @return the carName
22. */
23. public String getCarName() {
24. return carName;
25. }
26.
27. /**
28. * @return the carModel
29. */
30. public String getCarModel() {
31. return carModel;
32. }
33.
34. /**
35. * @param pCarName the carName to set
36. */
37. public void setCarName(String pCarName) {
38. carName = pCarName;
39. }
40.
41. /**
42. * @param pCarModel the carModel to set
43. */
44. public void setCarModel(String pCarModel) {
45. carModel = pCarModel;
46. }
47.
48. /**
49. * @see java.lang.Object#toString()
50. * @return
51. */
52. @Override
53. public String toString() {
54. return "my car name:[" + this.carName + "] model:[" + this.carModel
55. + "].";
56. }
57.
58. }
服务端接口的实现类：HelloHessianImpl.java
Java代码
1. package michael.hessian.impl;
2.
3. import java.util.ArrayList;
4. import java.util.HashMap;
5. import java.util.List;
6. import java.util.Map;
7.
8. import michael.hessian.HelloHessian;
9. import michael.hessian.MyCar;
10.
11. /**
12. * @author michael
13. *
14. */
15. public class HelloHessianImpl extends HessianServlet implements HelloHessian {
16.
17. public MyCar getMyCar() {
18. MyCar car = new MyCar();
19. car.setCarName("阿斯顿·马丁");
20. car.setCarModel("One-77");
21. return car;
22. }
23.
24. public Map<STRING,&NBSP;STRING> myBabays() {
25. Map<STRING,&NBSP;STRING> map = new HashMap<STRING,&NBSP;STRING>();
26. map.put("son", "孙吴空");
27. map.put("daughter", "孙小美");
28. return map;
29. }
30.
31. public List myLoveFruit() {
32. List list = new ArrayList();
33. list.add("apple");
34. list.add("kiwi");
35. list.add("orange");
36. return list;
37. }
38.
39. public String sayHello() {
40. return "welcom to Hessian";
41. }
42.
43. }
2.配置文件web.xml修改
在web.xml配置文件里增加如下信息：
Xml代码
1. <servlet>
2. <servlet-name>HelloHessian</< span>servlet-name>
3. <servlet-class>
4. com.caucho.hessian.server.HessianServlet
5. </< span>servlet-class>
6. <init-param>
7. <param-name>home-class</< span>param-name>
8. <param-value>michael.hessian.impl.HelloHessianImpl</< span>param-value>
9. </< span>init-param>
10. <init-param>
11. <param-name>home-api</< span>param-name>
12. <param-value>michael.hessian.HelloHessian</< span>param-value>
13. </< span>init-param>
14. <load-on-startup>1</< span>load-on-startup>
15. </< span>servlet>
16. <servlet-mapping>
17. <servlet-name>HelloHessian</< span>servlet-name>
18. <url-pattern>/HessianService</< span>url-pattern>
19. </< span>servlet-mapping>
20. <servlet-mapping>
3.java客户端验证
Java代码
1. package michael.hessian.client;
2.
3. import java.net.MalformedURLException;
4. import java.util.Map;
5.
6. import michael.hessian.HelloHessian;
7. import michael.hessian.MyCar;
8.
9. import com.caucho.hessian.client.HessianProxyFactory;
10.
11. /**
12. * @author michael
13. *
14. */
15. public class HessianClientTest {
16.
17. /**
18. * @param args
19. */
20. public static void main(String[] args) {
21. String url = "http://localhost:8082/J2EE_sjsky/HessianService";
22. HessianProxyFactory factory = new HessianProxyFactory();
23. try {
24. HelloHessian hello = (HelloHessian) factory.create(
25. HelloHessian.class, url);
26. System.out.println(hello.sayHello());
27.
28. MyCar car = hello.getMyCar();
29. System.out.println(car.toString());
30.
31. for (Map.Entry<STRING,&NBSP;STRING> entry : hello.myBabays().entrySet()) {
32. System.out.println(entry.getKey() + " " + entry.getValue());
33. }
34.
35. for (String str : hello.myLoveFruit()) {
36. System.out.println(str);
37. }
38.
39. } catch (MalformedURLException e) {
40. e.printStackTrace();
41. }
42.
43. }
44.
45. }
运行结果如下：
Java代码
1. welcom to Hessian
2. my car name:[阿斯顿·马丁] model:[One-77].
3. daughter 孙小美
4. son 孙吴空
5. apple
6. kiwi
7. orange
【二】、spring+hessian 实现服务端：
1.基本代码见上面的demo
2.修改配置文件
在web.xml，增加内容如下：
Xml代码
1. <servlet>
2. <servlet-name>springhessian</< span>servlet-name>
3. <servlet-class>
4. org.springframework.web.servlet.DispatcherServlet
5. </< span>servlet-class>
6.
7. <bean name="/helloHessianService"
8. class="org.springframework.remoting.caucho.HessianServiceExporter">
9.
10. <property name="service" ref="helloHessianImpl" />
11.
12. <property name="serviceInterface"
13. value="michael.hessian.HelloHessian" />
14. </< span>bean>
15. </< span>beans>
3.java客户端验证
和上面的例子相似，只需要把访问的url替换成新的即可如下：
Java代码
1. String url=http://localhost:8082/J2EE_sjsky/springhessian/helloHessianService
运行结果和上面例子一样。
4.spring配置客户端
增加一个spring的bean配置文件hessian-client.xml
Xml代码
1. <?xml version="1.0" encoding="UTF-8"?>
2. >
3. <beans>
4. <bean id="helloHessianClient"
5. class="org.springframework.remoting.caucho.HessianProxyFactoryBean">
6. <property name="serviceUrl">
7. <value>
8. http://localhost:8082/J2EE_sjsky/springhessian/helloHessianService
9. </< span>value>
10. </< span>property>
11. <property name="serviceInterface"
12. value="michael.hessian.HelloHessian" />
13. </< span>bean>
14. </< span>beans>
测试代码HessianSpringClient.java：
Java代码
1. package michael.hessian.client;
2.
3. import java.util.Map;
4.
5. import michael.hessian.HelloHessian;
6. import michael.hessian.MyCar;
7.
8. import org.springframework.context.ApplicationContext;
9. import org.springframework.context.support.ClassPathXmlApplicationContext;
10.
11. /**
12. * @author michael
13. *
14. */
15. public class HessianSpringClient {
16.
17. /**
18. * @param args
19. */
20. public static void main(String[] args) {
21. try {
22. ApplicationContext context = new ClassPathXmlApplicationContext(
23. "hessian-client.xml");
24.
25. HelloHessian hello = (HelloHessian) context
26. .getBean("helloHessianClient");
27.
28. System.out.println(hello.sayHello());
29.
30. MyCar car = hello.getMyCar();
31. System.out.println(car.toString());
32.
33. for (Map.Entry<STRING,&NBSP;STRING> entry : hello.myBabays().entrySet()) {
34. System.out.println(entry.getKey() + " " + entry.getValue());
35. }
36.
37. for (String str : hello.myLoveFruit()) {
38. System.out.println(str);
39. }
40. } catch (Exception e) {
41. e.printStackTrace();
42. }
43.
44. }
45.
46. }
运行结果和上面完全一致。
5.com.caucho.hessian.io.HessianProtocolException: expected string at 0x6d异常处理
我在spring+hessian整合测试过程中，客户端调用时，发生了异常，而服务端错误内容如下：
Java代码
1. 2011-4-25 16:14:44 org.apache.catalina.core.StandardWrapperValve invoke
2. 严重: Servlet.service() for servlet remoting threw exception
3. com.caucho.hessian.io.HessianProtocolException: expected string at 0x6d
4. at com.caucho.hessian.io.Hessian2Input.error(Hessian2Input.java:2882)
5. at com.caucho.hessian.io.Hessian2Input.expect(Hessian2Input.java:2830)
6. at com.caucho.hessian.io.Hessian2Input.readString(Hessian2Input.java:1362)
7. at com.caucho.hessian.io.Hessian2Input.readMethod(Hessian2Input.java:272)
8. at com.caucho.hessian.server.HessianSkeleton.invoke(HessianSkeleton.java:249)
9. at com.caucho.hessian.server.HessianSkeleton.invoke(HessianSkeleton.java:221)
10. at org.springframework.remoting.caucho.Hessian2SkeletonInvoker.invoke(Hessian2SkeletonInvoker.java:67)
11. at org.springframework.remoting.caucho.HessianServiceExporter.handleRequest(HessianServiceExporter.java:147)
12. at org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter.handle(HttpRequestHandlerAdapter.java:49)
13. at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:819)
14. at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:754)
15. at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:399)
16. at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:364)
17. at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
18. at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
19. at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
20. at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
21. at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
22. at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
23. at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
24. at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
25. at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
26. at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
27. at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
28. at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
29. at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
30. at java.lang.Thread.run(Thread.java:619)
