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HttpConnection.javaAPI DocJ2ME MIDP 2.031871Thu Nov 07 12:02:26 GMT 2002javax.microedition.io

HttpConnection

public interface HttpConnection implements javax.microedition.io.ContentConnection
This interface defines the necessary methods and constants for an HTTP connection.

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

  • Setup, in which the request parameters can be set
  • Connected, in which request parameters have been sent and the response is expected
  • Closed, the final state, in which the HTTP connection as been terminated
The following methods may be invoked only in the Setup state:
  • setRequestMethod
  • setRequestProperty
The transition from Setup to Connected is caused by any method that requires data to be sent to or received from the server.

The following methods cause the transition to the Connected state when the connection is in Setup state.

  • openInputStream
  • openDataInputStream
  • getLength
  • getType
  • getEncoding
  • getHeaderField
  • getResponseCode
  • getResponseMessage
  • getHeaderFieldInt
  • getHeaderFieldDate
  • getExpiration
  • getDate
  • getLastModified
  • getHeaderField
  • getHeaderFieldKey

The following methods may be invoked while the connection is in Setup or Connected state.

  • close
  • getRequestMethod
  • getRequestProperty
  • getURL
  • getProtocol
  • getHost
  • getFile
  • getRef
  • getPort
  • getQuery

After an output stream has been opened by the openOutputStream or openDataOutputStream methods, attempts to change the request parameters via setRequestMethod or the setRequestProperty are ignored. Once the request parameters have been sent, these methods will throw an IOException. When an output stream is closed via the OutputStream.close or DataOutputStream.close methods, the connection enters the Connected state. When the output stream is flushed via the OutputStream.flush or DataOutputStream.flush methods, the request parameters MUST be sent along with any data written to the stream.

The transition to Closed state from any other state is caused by the close method and the closing all of the streams that were opened from the connection.

Example using StreamConnection

Simple read of a URL using StreamConnection. No HTTP specific behavior is needed or used. (Note: this example ignores all HTTP response headers and the HTTP response code. Since a proxy or server may have sent an error response page, an application can not distinquish which data is retreived in the InputStream.)

Connector.open is used to open URL and a StreamConnection is returned. From the StreamConnection the InputStream is opened. It is used to read every character until end of file (-1). If an exception is thrown the connection and stream are closed.

void getViaStreamConnection(String url) throws IOException {
StreamConnection c = null;
InputStream s = null;
try {
c = (StreamConnection)Connector.open(url);
s = c.openInputStream();
int ch;
while ((ch = s.read()) != -1) {
...
}
} finally {
if (s != null)
s.close();
if (c != null)
c.close();
}
}

Example using ContentConnection

Simple read of a URL using ContentConnection. No HTTP specific behavior is needed or used.

Connector.open is used to open url and a ContentConnection is returned. The ContentConnection may be able to provide the length. If the length is available, it is used to read the data in bulk. From the ContentConnection the InputStream is opened. It is used to read every character until end of file (-1). If an exception is thrown the connection and stream are closed.

void getViaContentConnection(String url) throws IOException {
ContentConnection c = null;
DataInputStream is = null;
try {
c = (ContentConnection)Connector.open(url);
int len = (int)c.getLength();
dis = c.openDataInputStream();
if (len > 0) {
byte[] data = new byte[len];
dis.readFully(data);
} else {
int ch;
while ((ch = dis.read()) != -1) {
...
}
}
} finally {
if (dis != null)
dis.close();
if (c != null)
c.close();
}
}

Example using HttpConnection

Read the HTTP headers and the data using HttpConnection.

Connector.open is used to open url and a HttpConnection is returned. The HTTP headers are read and processed. If the length is available, it is used to read the data in bulk. From the HttpConnection the InputStream is opened. It is used to read every character until end of file (-1). If an exception is thrown the connection and stream are closed.

void getViaHttpConnection(String url) throws IOException {
HttpConnection c = null;
InputStream is = null;
int rc;

try {
c = (HttpConnection)Connector.open(url);

// Getting the response code will open the connection,
// send the request, and read the HTTP response headers.
// The headers are stored until requested.
rc = c.getResponseCode();
if (rc != HttpConnection.HTTP_OK) {
throw new IOException("HTTP response code: " + rc);
}

is = c.openInputStream();

// Get the ContentType
String type = c.getType();

// Get the length and process the data
int len = (int)c.getLength();
if (len > 0) {
int actual = 0;
int bytesread = 0 ;
byte[] data = new byte[len];
while ((bytesread != len) && (actual != -1)) {
actual = is.read(data, bytesread, len - bytesread);
bytesread += actual;
}
} else {
int ch;
while ((ch = is.read()) != -1) {
...
}
}
} catch (ClassCastException e) {
throw new IllegalArgumentException("Not an HTTP URL");
} finally {
if (is != null)
is.close();
if (c != null)
c.close();
}
}

Example using POST with HttpConnection

Post a request with some headers and content to the server and process the headers and content.

Connector.open is used to open url and a HttpConnection is returned. The request method is set to POST and request headers set. A simple command is written and flushed. The HTTP headers are read and processed. If the length is available, it is used to read the data in bulk. From the HttpConnection the InputStream is opened. It is used to read every character until end of file (-1). If an exception is thrown the connection and stream is closed.

void postViaHttpConnection(String url) throws IOException {
HttpConnection c = null;
InputStream is = null;
OutputStream os = null;
int rc;

try {
c = (HttpConnection)Connector.open(url);

// Set the request method and headers
c.setRequestMethod(HttpConnection.POST);
c.setRequestProperty("If-Modified-Since",
"29 Oct 1999 19:43:31 GMT");
c.setRequestProperty("User-Agent",
"Profile/MIDP-2.0 Configuration/CLDC-1.0");
c.setRequestProperty("Content-Language", "en-US");

// Getting the output stream may flush the headers
os = c.openOutputStream();
os.write("LIST games\n".getBytes());
os.flush(); // Optional, getResponseCode will flush

// Getting the response code will open the connection,
// send the request, and read the HTTP response headers.
// The headers are stored until requested.
rc = c.getResponseCode();
if (rc != HttpConnection.HTTP_OK) {
throw new IOException("HTTP response code: " + rc);
}

is = c.openInputStream();

// Get the ContentType
String type = c.getType();
processType(type);

// Get the length and process the data
int len = (int)c.getLength();
if (len > 0) {
int actual = 0;
int bytesread = 0 ;
byte[] data = new byte[len];
while ((bytesread != len) && (actual != -1)) {
actual = is.read(data, bytesread, len - bytesread);
bytesread += actual;
}
process(data);
} else {
int ch;
while ((ch = is.read()) != -1) {
process((byte)ch);
}
}
} catch (ClassCastException e) {
throw new IllegalArgumentException("Not an HTTP URL");
} finally {
if (is != null)
is.close();
if (os != null)
os.close();
if (c != null)
c.close();
}
}

Simplified Stream Methods on Connector

Please note the following: The Connector class defines the following convenience methods for retrieving an input or output stream directly for a specified URL:

  • InputStream openInputStream(String url)
  • DataInputStream openDataInputStream(String url)
  • OutputStream openOutputStream(String url)
  • DataOutputStream openDataOutputStream(String url)
Please be aware that using these methods implies certain restrictions. You will not get a reference to the actual connection, but rather just references to the input or output stream of the connection. Not having a reference to the connection means that you will not be able to manipulate or query the connection directly. This in turn means that you will not be able to call any of the following methods:
  • getRequestMethod()
  • setRequestMethod()
  • getRequestProperty()
  • setRequestProperty()
  • getLength()
  • getType()
  • getEncoding()
  • getHeaderField()
  • getResponseCode()
  • getResponseMessage()
  • getHeaderFieldInt
  • getHeaderFieldDate
  • getExpiration
  • getDate
  • getLastModified
  • getHeaderField
  • getHeaderFieldKey
since
MIDP 1.0

Fields Summary
public static final String
HEAD
HTTP Head method.
public static final String
GET
HTTP Get method.
public static final String
POST
HTTP Post method.
public static final int
HTTP_OK
200: The request has succeeded.
public static final int
HTTP_CREATED
201: The request has been fulfilled and resulted in a new resource being created.
public static final int
HTTP_ACCEPTED
202: The request has been accepted for processing, but the processing has not been completed.
public static final int
HTTP_NOT_AUTHORITATIVE
203: The returned meta-information in the entity-header is not the definitive set as available from the origin server.
public static final int
HTTP_NO_CONTENT
204: The server has fulfilled the request but does not need to return an entity-body, and might want to return updated meta-information.
public static final int
HTTP_RESET
205: The server has fulfilled the request and the user agent SHOULD reset the document view which caused the request to be sent.
public static final int
HTTP_PARTIAL
206: The server has fulfilled the partial GET request for the resource.
public static final int
HTTP_MULT_CHOICE
300: The requested resource corresponds to any one of a set of representations, each with its own specific location, and agent- driven negotiation information is being provided so that the user (or user agent) can select a preferred representation and redirect its request to that location.
public static final int
HTTP_MOVED_PERM
301: The requested resource has been assigned a new permanent URI and any future references to this resource SHOULD use one of the returned URIs.
public static final int
HTTP_MOVED_TEMP
302: The requested resource resides temporarily under a different URI. (Note: the name of this status code reflects the earlier publication of RFC2068, which was changed in RFC2616 from "moved temporalily" to "found". The semantics were not changed. The Location header indicates where the application should resend the request.)
public static final int
HTTP_SEE_OTHER
303: The response to the request can be found under a different URI and SHOULD be retrieved using a GET method on that resource.
public static final int
HTTP_NOT_MODIFIED
304: If the client has performed a conditional GET request and access is allowed, but the document has not been modified, the server SHOULD respond with this status code.
public static final int
HTTP_USE_PROXY
305: The requested resource MUST be accessed through the proxy given by the Location field.
public static final int
HTTP_TEMP_REDIRECT
307: The requested resource resides temporarily under a different URI.
public static final int
HTTP_BAD_REQUEST
400: The request could not be understood by the server due to malformed syntax.
public static final int
HTTP_UNAUTHORIZED
401: The request requires user authentication. The response MUST include a WWW-Authenticate header field containing a challenge applicable to the requested resource.
public static final int
HTTP_PAYMENT_REQUIRED
402: This code is reserved for future use.
public static final int
HTTP_FORBIDDEN
403: The server understood the request, but is refusing to fulfill it. Authorization will not help and the request SHOULD NOT be repeated.
public static final int
HTTP_NOT_FOUND
404: The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.
public static final int
HTTP_BAD_METHOD
405: The method specified in the Request-Line is not allowed for the resource identified by the Request-URI.
public static final int
HTTP_NOT_ACCEPTABLE
406: The resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.
public static final int
HTTP_PROXY_AUTH
407: This code is similar to 401 (Unauthorized), but indicates that the client must first authenticate itself with the proxy.
public static final int
HTTP_CLIENT_TIMEOUT
408: The client did not produce a request within the time that the server was prepared to wait. The client MAY repeat the request without modifications at any later time.
public static final int
HTTP_CONFLICT
409: The request could not be completed due to a conflict with the current state of the resource.
public static final int
HTTP_GONE
410: The requested resource is no longer available at the server and no forwarding address is known.
public static final int
HTTP_LENGTH_REQUIRED
411: The server refuses to accept the request without a defined Content- Length.
public static final int
HTTP_PRECON_FAILED
412: The precondition given in one or more of the request-header fields evaluated to false when it was tested on the server.
public static final int
HTTP_ENTITY_TOO_LARGE
413: The server is refusing to process a request because the request entity is larger than the server is willing or able to process.
public static final int
HTTP_REQ_TOO_LONG
414: The server is refusing to service the request because the Request-URI is longer than the server is willing to interpret.
public static final int
HTTP_UNSUPPORTED_TYPE
415: The server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.
public static final int
HTTP_UNSUPPORTED_RANGE
416: A server SHOULD return a response with this status code if a request included a Range request-header field , and none of the range-specifier values in this field overlap the current extent of the selected resource, and the request did not include an If-Range request-header field.
public static final int
HTTP_EXPECT_FAILED
417: The expectation given in an Expect request-header field could not be met by this server, or, if the server is a proxy, the server has unambiguous evidence that the request could not be met by the next-hop server.
public static final int
HTTP_INTERNAL_ERROR
500: The server encountered an unexpected condition which prevented it from fulfilling the request.
public static final int
HTTP_NOT_IMPLEMENTED
501: The server does not support the functionality required to fulfill the request.
public static final int
HTTP_BAD_GATEWAY
502: The server, while acting as a gateway or proxy, received an invalid response from the upstream server it accessed in attempting to fulfill the request.
public static final int
HTTP_UNAVAILABLE
503: The server is currently unable to handle the request due to a temporary overloading or maintenance of the server.
public static final int
HTTP_GATEWAY_TIMEOUT
504: The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server specified by the URI or some other auxiliary server it needed to access in attempting to complete the request.
public static final int
HTTP_VERSION
505: The server does not support, or refuses to support, the HTTP protocol version that was used in the request message.
Constructors Summary
Methods Summary
public longgetDate()
Returns the value of the date header field.

return
the sending date of the resource that the URL references, or 0 if not known. The value returned is the number of milliseconds since January 1, 1970 GMT.
exception
IOException if an error occurred connecting to the server.

public longgetExpiration()
Returns the value of the expires header field.

return
the expiration date of the resource that this URL references, or 0 if not known. The value is the number of milliseconds since January 1, 1970 GMT.
exception
IOException if an error occurred connecting to the server.

public java.lang.StringgetFile()
Returns the file portion of the URL of this HttpConnection.

return
the file portion of the URL of this HttpConnection. null is returned if there is no file.

public java.lang.StringgetHeaderField(java.lang.String name)
Returns the value of the named header field.

param
name of a header field.
return
the value of the named header field, or null if there is no such field in the header.
exception
IOException if an error occurred connecting to the server.

public java.lang.StringgetHeaderField(int n)
Gets a header field value by index.

return
the value of the nth header field or null if the array index is out of range. An empty String is returned if the field does not have a value.
param
n the index of the header field
exception
IOException if an error occurred connecting to the server.

public longgetHeaderFieldDate(java.lang.String name, long def)
Returns the value of the named field parsed as date. The result is the number of milliseconds since January 1, 1970 GMT represented by the named field.

This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.

param
name the name of the header field.
param
def a default value.
return
the value of the field, parsed as a date. The value of the def argument is returned if the field is missing or malformed.
exception
IOException if an error occurred connecting to the server.

public intgetHeaderFieldInt(java.lang.String name, int def)
Returns the value of the named field parsed as a number.

This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing.

param
name the name of the header field.
param
def the default value.
return
the value of the named field, parsed as an integer. The def value is returned if the field is missing or malformed.
exception
IOException if an error occurred connecting to the server.

public java.lang.StringgetHeaderFieldKey(int n)
Gets a header field key by index.

return
the key of the nth header field or null if the array index is out of range.
param
n the index of the header field
exception
IOException if an error occurred connecting to the server.

public java.lang.StringgetHost()
Returns the host information of the URL of this HttpConnection. e.g. host name or IPv4 address

return
the host information of the URL of this HttpConnection.

public longgetLastModified()
Returns the value of the last-modified header field. The result is the number of milliseconds since January 1, 1970 GMT.

return
the date the resource referenced by this HttpConnection was last modified, or 0 if not known.
exception
IOException if an error occurred connecting to the server.

public intgetPort()
Returns the network port number of the URL for this HttpConnection.

return
the network port number of the URL for this HttpConnection. The default HTTP port number (80) is returned if there was no port number in the string passed to Connector.open.

public java.lang.StringgetProtocol()
Returns the protocol name of the URL of this HttpConnection. e.g., http or https

return
the protocol of the URL of this HttpConnection.

public java.lang.StringgetQuery()
Returns the query portion of the URL of this HttpConnection. RFC2396 defines the query component as the text after the first question-mark (?) character in the URL.

return
the query portion of the URL of this HttpConnection. null is returned if there is no value.

public java.lang.StringgetRef()
Returns the ref portion of the URL of this HttpConnection. RFC2396 specifies the optional fragment identifier as the the text after the crosshatch (#) character in the URL. This information may be used by the user agent as additional reference information after the resource is successfully retrieved. The format and interpretation of the fragment identifier is dependent on the media type[RFC2046] of the retrieved information.

return
the ref portion of the URL of this HttpConnection. null is returned if there is no value.

public java.lang.StringgetRequestMethod()
Get the current request method. e.g. HEAD, GET, POST The default value is GET.

return
the HTTP request method
see
#setRequestMethod

public java.lang.StringgetRequestProperty(java.lang.String key)
Returns the value of the named general request property for this connection.

param
key the keyword by which the request property is known (e.g., "accept").
return
the value of the named general request property for this connection. If there is no key with the specified name then null is returned.
see
#setRequestProperty

public intgetResponseCode()
Returns the HTTP response status code. It parses responses like:
HTTP/1.0 200 OK
HTTP/1.0 401 Unauthorized
and extracts the ints 200 and 401 respectively. from the response (i.e., the response is not valid HTTP).

exception
IOException if an error occurred connecting to the server.
return
the HTTP Status-Code or -1 if no status code can be discerned.

public java.lang.StringgetResponseMessage()
Gets the HTTP response message, if any, returned along with the response code from a server. From responses like:
HTTP/1.0 200 OK
HTTP/1.0 404 Not Found
Extracts the Strings "OK" and "Not Found" respectively. Returns null if none could be discerned from the responses (the result was not valid HTTP).

exception
IOException if an error occurred connecting to the server.
return
the HTTP response message, or null

public java.lang.StringgetURL()
Return a string representation of the URL for this connection.

return
the string representation of the URL for this connection.

public voidsetRequestMethod(java.lang.String method)
Set the method for the URL request, one of:
  • GET
  • POST
  • HEAD
are legal, subject to protocol restrictions. The default method is GET.

param
method the HTTP method
exception
IOException if the method cannot be reset or if the requested method isn't valid for HTTP.
see
#getRequestMethod

public voidsetRequestProperty(java.lang.String key, java.lang.String value)
Sets the general request property. If a property with the key already exists, overwrite its value with the new value.

Note: HTTP requires all request properties which can legally have multiple instances with the same key to use a comma-separated list syntax which enables multiple properties to be appended into a single property.

param
key the keyword by which the request is known (e.g., "accept").
param
value the value associated with it.
exception
IOException is thrown if the connection is in the connected state.
see
#getRequestProperty