The HttpRequest Class in Java

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The HttpRequest Class
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the result of reading the document /etc/motd from the FTP server at ftpgimporg, using the URL ftp://ftpgimporg/etc/motd:
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 started -> true onStarted connecting -> true onConnecting doneConnect -> true onDoneConnect readingHeaders -> true onReadingHeaders onResponseHeaders content-length: 433 doneHeaders -> true onDoneHeaders reading -> true onReading toread -> 433 onToRead, length = 433 read -> 433 onRead: 433 bytes input -> comsunjavafxiohttpimplWaitingInputStream@1162212 onInput: 433 bytes doneRead -> true onDoneRead done -> true onDone
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If you compare this with the successful requests to an HTTP server shown in the A Request to a Valid HTTP URL section, earlier in this chapter, you see that the lifecycle is broadly the same the connection is made on lines 1 to 6, the receipt of data is reported on lines 12 to 17, the data is made available to be read via an InputStream on lines 18 and 19, and the lifecycle concludes with the done variable being set to true on lines 22 and 23 However, because this example uses the FTP protocol rather than HTTP, there is no response code, no response message, and only a single header that reports the size of the document being retrieved Even this header is not real it is constructed based on information returned by the FTP serverThe data can be read (and in fact must be read, for the same reason as data returned from an HTTP server must be read) from the InputStream stored in the input variable and passed to the onInput callback, in the same way as any other HttpRequest
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PUT Requests
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An HTTP PUT request is typically used to upload new data to a web serverThe data is supplied in the body of the request, following the headersThe HttpRequest class provides a small number of variables and callback functions, in addition to those listed in Table 27-1 that are used when uploading dataThese variables and callbacks are listed in Table 27-2
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Table 27-2 Variables and Callback Functions That Track the Status of an HTTP PUT or HTTP POST Request Variable Type
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Boolean OutputStream
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Variable
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writing output
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Function
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onWriting onOutput
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Function Argument Type
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None
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Output Stream
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Set/Function Called
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Just before the request data is written When the request data is required Not set or called when the source variable is not null See the text for details When the data to be written has been supplied and is about to be written As bytes of request data are written May be set/called multiple times When all the request data has been written
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toWrite
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Long
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onToWrite
Long
written
Long
onWritten
Long
doneWrite
Boolean
onDoneWrite
None
When uploading data, you need to set the HTTP headers that indicate the type of the data, its encoding, and its lengthThe headers variable of the HttpRequest object is provided for this purposeThe data itself can be supplied in either of two ways you can wrap it in an InputStream and reference it from the source variable, or you can allow the HttpRequest class to create an OutputStream that you write to when the data is requiredWe ll show both possibilities in this section The example code in the file javafxdata/HttpRequestExample4fx performs a PUT request and supplies its data via the source variable Like the rest of the examples in this section, it uses a servlet that you need to compile and deploy In the Preface to this book, you will find instructions for installing the integrated development environment (IDE) plug-ins required to run the servletTo start the servlet, right click the ExternalData project in the IDE and click Run Here, we assume that the servlet is running in a web container that is listing on port 8080 of the same computer as the one on which the examples are being runWhen you run the example, you will see a familiar user interface that allows you to enter a URL, initiate the request, and then view the results, as shown in Figure 27-3 The URL used is http://localhost:8080/ExternalData/HttpRequestServlet/a/b/c/d The first part of this URL (up to and including HttpRequestServlet) refers to the servlet itselfThe balance of the URL is the name of a file into which the uploaded data is to be stored In fact, the servlet does not actually store the data it just returns a response