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matlab.net.http.io.JSONConsumer Class

Namespace: matlab.net.http.io
Superclasses: matlab.net.http.io.StringConsumer

Content consumer that converts JSON input into MATLAB data

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Description

This ContentConsumer receives messages whose content is JSON. It converts the JSON data to MATLAB® and stores the result in the body of the response message.

This consumer should only be applied to incoming content that is JSON (for example, response messages or parts of multipart messages with a Content-Type of "application/json"), though it does not check the incoming Content-Type.

By default, MATLAB automatically converts a message with a Content-Type "application/json", so you do not need to specify this consumer for that type, or any other type that obviously indicates JSON. For more information, see input conversions for MessageBody.Data. Specify this provider explicitly if you know that the incoming data is JSON even if the Content-Type might not indicate this. For example, sometimes a file containing JSON data has a name with a .txt extension. When downloading such a file the server might specify a Content-Type of "text/plain" based on that extension, even though it contains JSON data.

If an error occurs converting the data, Response.Body.Data in the HTTPException thrown on the error contains any intermediate result of the decoding process.

The matlab.net.http.io.JSONConsumer class is a handle class.

Creation

Description

consumer = JSONConsumer creates a consumer that converts a JSON string received in a ResponseMessage to MATLAB data using jsondecode.

Properties

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Public Properties

The character set used to convert the data, specified as a string. This value is initially empty. If you leave it empty, then this value is set when a message is received, based on the specified or default charset in the Content-Type field of the message. If you want to force conversion using a different charset, then you can do so by specifying a charset in the StringConsumer constructor, or directly setting this property. Subclasses can set this property at any time, including in the middle of a message. If you change this value after calling putData, then the new value is used in subsequent calls to putData. The existing contents of Response.Body.Data is not changed.

When receipt of a response begins, if this property was initially left empty, then MATLAB sets this property to the chosen charset based on the Content-Type. If you reuse this consumer for a different message, then a new charset can be chosen. If you set this property to a nonempty value, MATLAB never changes it.

Attributes:

GetAccess
public
SetAccess
public
Dependent
true

Suggested buffer size, specified as uint64. MATLAB sets AllocationLength to the anticipated size of buffers of data passed to putData. The actual size might be smaller or larger. To improve performance, the consumer can use this value to preallocate space to handle the data.

MATLAB sets this property before calling the start method for the convenience of subclasses.

Attributes:

GetAccess
public
SetAccess
public

Expected length of the payload, specified as uint64. The property normally is the Value property of the matlab.net.http.field.ContentLengthField in the Header property.

If ContentLength is empty, then the length is not known. The payload ends when putData(uint8.empty) is called.

MATLAB sets this property before calling initialize, for the convenience of subclasses that might benefit from knowing the length of the data.

If this ContentConsumer is a delegate of a top-level consumer, then the value of ContentLength might be different from the ContentLength value of the top-level consumer.

Example: numel(someData) where someData is type uint8

Attributes:

GetAccess
public
SetAccess
public

Media type of payload, specified as a matlab.net.http.MediaType object. The property normally is the Value property of the matlab.net.http.field.ContentTypeField in the Header property. If the ContentType property is empty, then the ContentTypeField is empty or nonexistent.

MATLAB sets this property before calling initialize for the convenience of subclasses that might want to examine the MediaType. Subclasses can set this property if they determine from the data that it is of a different MediaType.

At the end of the transfer, MATLAB copies this value into the Response.Body.ContentType property.

Example: 'application/octet-stream'

Attributes:

GetAccess
public
SetAccess
public

Header of the payload currently being processed, specified as a matlab.net.http.HeaderField object.

Consumers use this header to determine how to process the payload that is being sent to them. For a top-level consumer, this value is the same as Response.Header. For a delegate, the value might be different. For example, in a multipart message processed by a MultipartConsumer, it is the header of the part that this delegate is processing. The delegate can still examine Response.Header for headers of the original message.

MATLAB sets this property before calling initialize, for the convenience of subclasses.

Attributes:

GetAccess
public
SetAccess
public

The completed RequestMessage that was sent, specified as a matlab.net.http.RequestMessage object. This is the final RequestMessage after all redirections, which is the completedrequest return value from the send method.

MATLAB sets this property before calling initialize, for the convenience of subclasses.

Attributes:

GetAccess
public
SetAccess
public

The ResponseMessage being processed, specified as a matlab.net.http.ResponseMessage object.

MATLAB sets the Response property before calling initialize. The value is the ResponseMessage after headers have been received but before receiving any payload. At the start of the response message processing (or the start of a part for multipart messages), the ResponseMesssage.Body property is a MessageBody object with empty Data and Payload properties. To store received data, consumers can modify the Response and MessageBody.Data properties during data transfer. Usually, consumers that process and then store data set Response.Body.Data to their processed payload, though this is not required. At the completion of the transfer, MATLAB returns this Response to the caller of send. Consumers should not modify other Response properties, such as Header or StatusLine, as those changes are returned to the caller of send.

The Response.Body.Payload property is empty during the transfer and consumers should not attempt to modify it. If the HTTPOptions.SavePayload property is set, then MATLAB sets Payload to the received payload at the end of the transfer of the message or the part (after the call to putData(uint8.empty)) or when an exception occurs.

If an exception occurs in the consumer during message processing, then MATLAB throws an HTTPException object. The History property contains this Response value.

If the consumer is a delegate that is processing part of a multipart message, then Response.Header contains the header of the whole message, and the Payload and Data properties of Response.Body are cleared before invoking the ContentConsumer for each part. At the conclusion of each part, a new ResponseMessage is added to the end of the array of ResponseMessage objects in the original response's Body.Data containing the Header from this object and the Body from this property. The next delegate sees a fresh Response with an empty MessageBody, not the previous delegate's MessageBody.

Attributes:

GetAccess
public
SetAccess
public
Dependent
true

Destination of the request being processed, specified as a matlab.net.URI object. This value is the original destination URI as determined by send. It is not the URI of a proxy or the final URI after redirections.

MATLAB sets this property before calling initialize, for the convenience of subclasses.

Attributes:

GetAccess
public
SetAccess
public

Protected Properties

Function, specified as a function handle, called by the putData method to append additional data. The putData method in this class calls the AppendFcn function to append data it receives in its data argument to existing data in the response message. The function must have the signature:

AppendFcn(consumer,newdata)

where newdata is the data to be appended to the array at consumer.Response.Body.Data. It is the responsibility of this method to update consumer.CurrentLength to reflect the new length of Data. If newdata is empty, which indicates the end of the stream, then the function should update Response.Body.Data to its final value.

The default behavior, if this property is empty, uses an internal function that treats Data as an array of arbitrary values supporting the horzcat function. It efficiently adds newdata by preallocating space, maintaining CurrentLength to be the actual length of data stored. At the end of the message, it truncates Response.Body.Data to CurrentLength.

Subclasses can change this property if horzcat is not appropriate for the append process. For example, when a StringConsumer builds a scalar string, it would add to the string using the plus function instead of horzcat.

Subclasses that do not invoke ContentConsumer.putData to append data, or which are satisfied with horzcat behavior when appending data, can ignore this property.

Example: @customAppend where @customAppend is defined by the consumer

Attributes:

GetAccess
protected
SetAccess
protected

The ContentConsumer to which this consumer is delegating, specified as a matlab.net.http.io.ContentConsumer object. The delegateTo method of the calling consumer (the delegator) sets the CurrentDelegate property. If there is no current delegation, then the value is [].

MATLAB sets CurrentDelegate to [] before calling initialize.

Attributes:

GetAccess
protected
SetAccess
protected

Length of data currently in the Response.Body.Data property, specified as uint64.

This property is used when Response.Body.Data has been preallocated to a size larger than the actual amount of data currently stored, to indicate the length of that stored data. If this property is empty, then it means that all of Response.Body.Data contains the stored data or that a ContentConsumer subclass is disposing of the data in some way other than storing it in Response.Body.Data.

This property is used and set by the putData method in this base class when the AppendFcn property is empty. It is for the benefit of subclasses that call putData and want to examine already-stored data, and/or any implementations of AppendFcn that maintain results in Response.Body.Data.

Subclasses that use putData also can modify this property to reset the position in the buffer where the data is stored. For example, when the default AppendFcn function is used, a subclass that processes all of Response.Body.Data on each call to putData might no longer have a use for the original data, so it can reset the CurrentLength property to 1 so that the next putData call overwrites the buffer with new data. There is no need to clear elements in the buffer past the end of the new data.

Subclasses that do not call putData can use this property to track their own data, or can leave it unset (empty). MATLAB does not place any constraints on the value that can be set here and does not use it for any purpose other than to determine where the default AppendFcn should store the next buffer of data, and where to truncate the data at the end of the message. Set this property to empty before the final call to putData(uint8.empty) to prevent truncation of the data.

MATLAB sets this property to empty before each call to initialize.

Attributes:

GetAccess
protected
SetAccess
protected

The ContentConsumer that delegated to this consumer, specified as a matlab.net.http.io.ContentConsumer object. If this consumer is a delegate that was invoked by another consumer, such as a GenericConsumer or MultipartConsumer, then this is the calling consumer. It is empty in a top-level consumer specified in the call to send.

Delegates can use this property to access properties of their delegators, for example, to determine which consumer delegated to them.

Attributes:

GetAccess
protected
SetAccess
protected

Methods

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More About

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Version History

Introduced in R2018a

See Also

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