Filter Modules in Java Add PDF 417 in Java Filter Modules

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8 Filter Modules using swing todisplay pdf 417 for web,windows application QR Code Overview /** The ty PDF417 for Java pe of filter, either AP_FTYPE_CONTENT or AP_FTYPE_CONNECTION. * An AP_FTYPE_CONTENT filter modifies the data based on information * found in the content. An AP_FTYPE_CONNECTION filter modifies the * data based on the type of connection.

*/ ap_filter_type ftype; /** The next filter_rec in the list */ struct ap_filter_rec_t *next; /** Providers for this filter */ ap_filter_provider_t *providers; /** Trace level for this filter */ int debug; /** Protocol flags for this filter */ unsigned int proto_flags; };. The name i s just an identifier for the filter configuration, which will be discussed in 9. The filter_func is the main callback we ve already introduced, and the filter_init_func is a seldom-used initialization function that is called when the filter is inserted and before the first data are available. The final three fields were introduced with the smart filtering architecture in Apache 2.

2, as described in Section 8.7..

8.6 Filter I/O Data passe s through the filter chain on the bucket brigade. There are several strategies for dealing with the data in a filter: If the filter merely looks at the data but doesn t change anything, it can pass the brigade on as is. If the filter makes changes but preserve content length (e.

g., a case filter for ASCII text), it can replace bytes in place. A filter that passes through most of the data intact but makes some changes can edit the data by direct bucket manipulation.

A filter that completely transforms the data will often need to replace the data completely, by creating an entirely new brigade and populating it. It. 8.7 Smart Filtering in Apache 2.2 can do so either directly or by using stdio-like functions. Two families of stdio-like functions are available: APR provides apr_brigade_puts/ apr_brigade_write/etc., while util_filter provides ap_fwrite/ ap_fputs/ap_fprintf/etc.

Management of I/O lies at the heart of filtering. It will be demonstrated at length when we develop example filters later in this chapter. The key concepts in managing data are the bucket and the brigade.

We have already encountered them in 3 and elsewhere. In this chapter, our examples will explore them in depth..

8.7 Smart Filtering in Apache 2.2 The origin al Apache 2.0 filter architecture presents problems when used with unknown content whether in a proxy or with a local handler that generates different content types to order. The basic difficulty derives from the Apache configuration.

Content filters need to be applied conditionally. For example, we don t want to pass images through an HTML filter. Apache 2.

0 provides four generic configuration directives for filters: SetOutputFilter: Unconditionally insert a filter. AddOutputFilter, RemoveOutputFilter: Insert or remove a filter based on extension. AddOutputFilterByType: Insert a filter based on content type.

This directive is implemented in the ap_set_content_type function, and has complex side effects. In the case of a proxy, extensions are meaningless, as we cannot know what conventions an origin server might adopt. Likewise, when the server generates content dynamically or filters it dynamically with, for example, XSLT it can be difficult or even impossible to configure the filter chain using the preceding directives.

Instead, we have to resort to the unsatisfactory hack of inserting a filter unconditionally, checking the response headers from the proxy, and then having the filter remove itself where appropriate. Examples of filters that follow this approach include mod_deflate, mod_xmlns, mod_accessibility, and mod_proxy_html..

8 Filter Modules 8.7.1 Preprocessing and Postprocessing As with an barcode pdf417 for Java origin server, it may be necessary to preprocess data before the data go through the main content-transforming filter and/or to postprocess the data afterward. For example, when dealing with gzipped content, we need to uncompress it for processing and then recompress the processed data. Similarly, in an imageprocessing filter, we need to decode the original image format and re-encode the processed data.

This may involve more than one phase. For example, when filtering text, we may need both to uncompress gzipped data and to transcode the character set before the main filter. Potentially, then, we have a large multiplicity of filters: transformation filters, together with preprocessing and postprocessing for different content types and encodings (see Figures 8-3 and 8-4).

To repeat the hack of each filter being inserted and determining whether to run or remove itself in such a setup goes beyond simple inelegance and into the absurd. An alternative architecture is required..

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