客户端的调用
Web services提供的服务多种多样，有的可以马上获得结果，有的要消耗很长的时间。所以，假如我们需要多种调用方式来对付不同的情况。
大多数的Web services都提供阻塞(Blocking)和非阻塞(Non-Blocking)两种APIs.这两个概念以前应该学过，简单说一下。
Blocking API - 调用端要等被调用的函数运行完毕才继续往下走。
Non-Bloking API - 调用端运行完调用函数以后就直接往下走了，调用端和被调用端是异步执行的。返回值是用回调函数来实现的。
这种异步叫做API层异步（API Level Asynchrony）。他们只用到一个连接来发送和接收消息，而且，假如是那种需要运行很长时间的函数，还会碰到Time Out 错误，假如用两个连接分别处理发送和接收消息，调用的时间就可以缩短，也可以解决Time Out 问题。用两个连接来分别处理发送和接收消息，叫做传输层异步（Transport Level Asynchrony）。
理论真无聊，还是来看实例吧。
打开 Eclipse, 创建一个新PRoject, 新建一个叫userguide.clients的包, 把"samples\userguide\src\userguide\clients" 下面的文件都copy到那个包下面, 把AXIS2的lib下面的jar都加到ilbrary里面去(应该不用全加,懒一点就全加了吧.) 发现了关于echo的调用的方式, 居然有五个:
EchoBlockingClient
EchoBlockingDualClient
EchoBlockingWsaBasedClient
EchoNonBlockingClient
EchoNonBlockingDualClient
一个一个看吧.
EchoBlockingClient.java
public class EchoBlockingClient {
private static EndpointReference targetEPR = new EndpointReference("http://localhost:8080/axis2/services/MyService");
public static void main(String[] args) {
try {
OMElement payload = ClientUtil.getEchoOMElement();
Call call = new Call();
call.setTo(targetEPR);
call.setTransportInfo(Constants.TRANSPORT_HTTP,
Constants.TRANSPORT_HTTP,
false);
//Blocking invocation
OMElement result = call.invokeBlocking("echo",
payload);
StringWriter writer = new StringWriter();
result.serializeWithCache(xmlOutputFactory.newInstance()
.createXMLStreamWriter(writer));
writer.flush();
System.out.println(writer.toString());
} catch (AxisFault axisFault) {
axisFault.printStackTrace();
} catch (XMLStreamException e) {
e.printStackTrace();
}
}
}
和一代几乎一样, 弄一个EndpointReference, 再弄一个call, 其他不一样,但是也很简单， 弄一个OMElement作为参数, 返回也是一个OMElement. 可惜运行居然有错.
再来看双通道的版本
EchoBlockingDualClient.java
public class EchoBlockingDualClient {
private static EndpointReference targetEPR = new EndpointReference("http://127.0.0.1:8080/axis2/services/MyService");
public static void main(String[] args) {
try {
OMElement payload = ClientUtil.getEchoOMElement();
Call call = new Call();
call.setTo(targetEPR);
call.engageModule(new QName(Constants.MODULE_ADDRESSING));
call.setTransportInfo(Constants.TRANSPORT_HTTP,
Constants.TRANSPORT_HTTP,
true);
//Blocking Invocation
OMElement result = call.invokeBlocking("echo",
payload);
StringWriter writer = new StringWriter();
result.serializeWithCache(XMLOutputFactory.newInstance()
.createXMLStreamWriter(writer));
writer.flush();
System.out.println(writer.toString());
//Need to close the Client Side Listener.
call.close();
} catch (AxisFault axisFault) {
axisFault.printStackTrace();
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
加了一句engageModule, 这句话似乎没什么用，我删掉这句话也能运行的, 然后setTransportInfo最后一个参数改成了true. 关于setTransportInfo的三个参数, 第一个是发送的Transport, 第二个是接收的Transport, 第三个是"是否双通道", 支持的搭配形式如下:
http, http, true
http, http, false
http,smtp,true
smtp,http,true
smtp,smtp,true
看下一个吧，EchoNonBlockingClient，这个是单通道的非阻塞模式：
public class EchoNonBlockingClient {
private static EndpointReference targetEPR = new EndpointReference("http://127.0.0.1:8080/axis2/services/MyService");
public static void main(String[] args) {
try {
OMElement payload = ClientUtil.getEchoOMElement();
Call call = new Call();
call.setTo(targetEPR);
call.setTransportInfo(Constants.TRANSPORT_HTTP,
Constants.TRANSPORT_HTTP,
false);
//Callback to handle the response
Callback callback = new Callback() {
public void onComplete(AsyncResult result) {
try {
StringWriter writer = new StringWriter();
result.getResponseEnvelope().serializeWithCache(XMLOutputFactory.newInstance()
.createXMLStreamWriter(writer));
writer.flush();
System.out.println(writer.toString());
} catch (XMLStreamException e) {
reportError(e);
}
}
public void reportError(Exception e) {
e.printStackTrace();
}
};
//Non-Blocking Invocation
call.invokeNonBlocking("echo", payload, callback);
//Wait till the callback receives the response.
while (!callback.isComplete()) {
Thread.sleep(1000);
}
} catch (AxisFault axisFault) {
axisFault.printStackTrace();
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
不同的地方，只是调用的方法从invokeBlocking变成了invokeNonBlocking，然后写了一个简单的匿名Callback类作为回调函数。关于这个Callback类，它是一个抽象类，其中有两个方法：onComplete和reportError，都是client端必须实现的，他还有一个Field，就是complete，可以用来设置和查询调用是否完成。可惜也不能运行，和上面的错误一样，是在createSOAPMessage的时候报null错误。
看下一个EchoNonBlockingDualClient，非阻塞的双通道：
public class EchoNonBlockingDualClient {
private static EndpointReference targetEPR = new EndpointReference("http://127.0.0.1:8080/axis2/services/MyService");
public static void main(String[] args) {
try {
OMElement payload = ClientUtil.getEchoOMElement();
Call call = new Call();
call.setTo(targetEPR);
//The boolean flag informs the axis2 engine to use two separate transport connection
//to retrieve the response.
call.engageModule(new QName(Constants.MODULE_ADDRESSING));
call.setTransportInfo(Constants.TRANSPORT_HTTP,
Constants.TRANSPORT_HTTP,
true);
//Callback to handle the response
Callback callback = new Callback() {
public void onComplete(AsyncResult result) {
try {
StringWriter writer = new StringWriter();
result.getResponseEnvelope().serializeWithCache(XMLOutputFactory.newInstance()
.createXMLStreamWriter(writer));
writer.flush();
System.out.println(writer.toString());
} catch (XMLStreamException e) {
reportError(e);
}
}
public void reportError(Exception e) {
e.printStackTrace();
}
};
//Non-Blocking Invocation
call.invokeNonBlocking("echo", payload, callback);
//Wait till the callback receives the response.
while (!callback.isComplete()) {
Thread.sleep(1000);
}
//Need to close the Client Side Listener.
call.close();
} catch (AxisFault axisFault) {
axisFault.printStackTrace();
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
双通道和单通道基本没什么不同，只是双通道的时候，它总是要
