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
------------------------------------------------------------
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: