j2me 联网技术分析总结

基本点:

Generic Connections

In the CLDC Generic Connection framework, all connections are created using the open static method from the Connector class. If successful, this method returns an object that implements one of the generic connection interfaces. Figure 1 shows how these interfaces form an is-a hierarchy. The Connection interface is the base interface such that StreamConnectionNotifier is a Connection and InputConnection is a Connection too.

Figure 1: Connection interface hierarchy

• The Connection interface is the most basic connection type. It can only be opened and closed.
• The InputConnection interface represents a device from which data can be read. Its openInputStream method returns an input stream for the connection.
• The OuputConnection interface represents a device to which data can be written. Its openOutputStream method returns an output stream for the connection.
• The StreamConnection interface combines the input and output connections.
• The ContentConnection is a subinterface of StreamConnection. It provides access to some of the basic meta data information provided by HTTP connections.
• The StreamConnectionNotified waits for a connection to be established. It returns a StreamConnection on which a communication link has ben established.
• The DatagramConnection represents a datagram endpoint.

The open method of the Connector class has the following syntax, where the String parameter has the format "protocol:address;parameters".

<!---->Connector.open(String);

Here are a few examples:

HTTP Connection

<!---->Connector.open("http://java.sun.com/developer");

Datagram Connection

<!---->Connector.open("datagram://address:port#");

Communicate with a Port

<!---->Connector.open("comm:0;baudrate=9600');

Open Files

<!---->Connector.open("file:/myFile.txt");

The HttpConnection Interface:

The HTTP protocol is a request-response application protocol in which the parameters of the request must be set before the request is sent. The connection could be in one of the three following states:

• Setup: No connection yet
• Connected: Connection has been made, the request has been sent, and some response is expected
• Closed: Connection is closed

In the setup state the following methods can be invoked:

• setRequestMethod
• setRequestProperty

For example, suppose you have this connection:

<!---->HttpConnection c = (HttpConnection)
Connector.open("http://java.sun.com/developer");

Then, you can set the request method to be of type POST as follows:

<!---->c.setRequestMethod(HttpConnection.POST);

And likewise, you can set some of the HTTP properties. For example, you can set the User-Agent as follows:

<!---->c.setRequestProperty("User-Agent","Profile/MIDP-1.0 Configuration/CLDC-1.0");

If there is a method that requires data to be sent or received from the server, there is a state transition from Setup to Connected. Examples of methods that cause the transition include:

<!---->openInputStream
openOutputStream
openDataInputStream
openDataOutputStream
getLength
getType
getDate
getExpiration

And while the connection is open, some of these methods that may be invoked:

<!---->getURL
getProtocol
getHost
getPort

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要注意的问题:
开发中遇到个很头疼的问题, 与服务器通信write()数据时报java.io.IOException: Couldn't write to socket.
但是服务器抓不到任何包. 一开始怀疑是连建立连接出的问题, 实际上服务器抓不到包也有可能是流在没有close的时候就已经报错了.
如:
conn.open("url");
out = conn.openDataOutputStream();//此时将进行与服务器的三次握手;
                                  //但是如果在out.close()之前出现异常服务器是抓不到任何包的
out.write(byte[] bb);

关于这个的解释应该是流的缓冲机制.
所以正确的写法应该是捕捉到异常之后在catch块中把流close掉.
服务器端开发人员一般会说收不到包所以连接有问题,会把责任推给客户端,抓住这个证据在跟服务器端的同事扯皮时将处于有利的位置,嘎嘎.
还有就是要多做小实验, 注意代码要规范严格.

发现的几个问题:
1. java.io.IOException: Couldn't write to socket

2. java.io.IOException: Couldn't read from socket

CMNET联网方案:

CMWAP联网方案:

移动资费页的处理:

一个通用的HTTP连接封装:

评论

2 楼 yekai584341028 2011-01-07  

楼主太搞笑了，还和服务器扯皮呵呵。
捕获异常要捕获根源异常。

1 楼 xmmarmy007 2009-01-16  

java.io.IOException: Couldn't read from socket
我在开发过程中读取服务器的数据遇到这个异常，一般是什么原因引起的呢？