Task

<follow>

When a given file or resource grows, then this task processes the data that was added, e.g. it prints it to STDOUT.

The name refers to the 'follow mode' of the LESS utility (or the 'follow' option of the TAIL command), which does more or less the same.

For files, it is easy and fast to test whether a file has grown; for other resources it is not. For resources url="..." addressed by an HTTP URL}, the following optimizations are implemented:

• Instead of reading the resource repeatedly, its size and modification are checked with a HEAD request.
• Instead of reading the entire contents of the resource repeatedly, only the part that was (presumably) added is retrieved by using the "Range" request header.

The following attributes are mutually exclusive:

httpChunkLength="..."

httpContentLength="..."

Also the following attributes and subelements are mutually exclusive:

url="..."

<url>

Also the following attributes are mutually exclusive:

direct="..."

httpProxy="..."

socksProxy="..."

Attribute Summary

Attributes

Name	Description
allowUserInteraction="..."	Whether the underlying URL should be examined in a context in which it makes sense to allow user interactions, such as popping up an authentication dialog.
connectTimeout="..."	The timeout, in milliseconds, to be used when opening a communications link to the resource referenced by the underlying URLConnection.
direct="..."	Configures a direct HTTP connection, and ignores any proxy configured with the http[s].proxy(Host|Port) system properties.
httpChunkLength="..."	Enables the "chunked streaming mode".
httpContentLength="..."	Enables the "fixed length streaming mode".
httpFollowRedirects="..."	Whether HTTP redirects (requests with response code 3xx) should be automatically followed.
httpFollowRedirects2="..."	Similar to httpFollowRedirects="...", but additionally allows for redirects across protocols, e.g. from "http://host/index.html" to "https://host/index.html".
httpProxy="..."	Configures an HTTP proxy, and overrides any proxy configured with the http[s].proxy(Host|Port) system properties.
ifModifiedSince="..."	Set the value of the ifModifiedSince field of the underlying URLConnection.
readTimeout="..."	The read timeout, in milliseconds.
socksProxy="..."	Configures a SOCKS proxy, and overrides any proxy configured with the http[s].proxy(Host|Port) system properties.
url="..."	Designates the resource to access.
useCaches="..."	Set the value of the useCaches field of the underlying URLConnection.
encoding="..."	If a org.apache.tools.ant.types.FilterChain is configured, then the data from the file is DECODED with this encoding, then fed through the <filterchain>, and then ENCODED again.
failOnTimeout="..."	Whether the execution of the current target should fail or not if the file size does not change.
file="..."	The file to monitor.
outputFile="..."	Write the additional data to the named file.
periodTime="..."	The period in milliseconds to check the file's size.
stderr="..."	Write the additional data to STDERR.
stdout="..."	Write the additional data to STDOUT.
timeout="..."	The time (in seconds) when to give up if the file size does not change.

Subelement Summary

Subelements

Name	Description
<requestProperty>	Configures a "request property".
<url>	Designates the resource to access.
Any FilterChain	If given, then the data that is added to the file is fed through this filter chain, and the task will complete only when the filter chain produces some output.

Attribute Detail

Default values are underlined.

file="file"

The file to monitor.

outputFile="output-file"

Write the additional data to the named file.

stdout="true|false"

Write the additional data to STDOUT.

stderr="true|false"

Write the additional data to STDERR.

encoding="encoding"

If a org.apache.tools.ant.types.FilterChain is configured, then the data from the file is DECODED with this encoding, then fed through the <filterchain>, and then ENCODED again. Defaults to the system default encoding.

periodTime="period-time|500"

The period in milliseconds to check the file's size.

timeout="timeout|300"

The time (in seconds) when to give up if the file size does not change. A value of '0' indicates to wait indefinitely.

failOnTimeout="true|false"

Whether the execution of the current target should fail or not if the file size does not change.

allowUserInteraction="true|false"

Whether the underlying URL should be examined in a context in which it makes sense to allow user interactions, such as popping up an authentication dialog.

See also:

URLConnection.setAllowUserInteraction(boolean)

connectTimeout="milliseconds"

The timeout, in milliseconds, to be used when opening a communications link to the resource referenced by the underlying URLConnection. If the timeout expires before the connection can be established, a SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.

See also:

URLConnection.setConnectTimeout(int)

readTimeout="milliseconds"

The read timeout, in milliseconds. If the timeout expires before there is data available for read, a SocketTimeoutException is raised. A timeout of zero is interpreted as an infinite timeout.

See also:

URLConnection.setReadTimeout(int)

ifModifiedSince="point-of-time"

Set the value of the ifModifiedSince field of the underlying URLConnection.

See also:

URLConnection.setIfModifiedSince(long)

useCaches="true|false"

Set the value of the useCaches field of the underlying URLConnection.

See also:

URLConnection.setUseCaches(boolean)

httpChunkLength="chunk-length"

Enables the "chunked streaming mode". A negative value or zero configures a "default chunk size" (typically 4096 bytes), otherwise the given chunk length.

See also:

HttpURLConnection.setChunkedStreamingMode(int)

httpContentLength="..."

httpContentLength="content-length"

Enables the "fixed length streaming mode". The given value must equal the number of bytes that pose the request body, or an error will occur.

See also:

HttpURLConnection.setFixedLengthStreamingMode(int)

httpChunkLength="..."

httpFollowRedirects="true|false"

Whether HTTP redirects (requests with response code 3xx) should be automatically followed.

See also:

httpFollowRedirects2="..."

HttpURLConnection.setFollowRedirects(boolean)

httpFollowRedirects2="true|false"

Similar to httpFollowRedirects="...", but additionally allows for redirects across protocols, e.g. from "http://host/index.html" to "https://host/index.html".

url="u-r-l"

Designates the resource to access.

direct="true|false"

Configures a direct HTTP connection, and ignores any proxy configured with the http[s].proxy(Host|Port) system properties.

See also:

URL.openConnection(Proxy)

Proxy.NO_PROXY

NetworkingProperties

httpProxy="hostname:port"

Configures an HTTP proxy, and overrides any proxy configured with the http[s].proxy(Host|Port) system properties.

See also:

URL.openConnection(Proxy)

Proxy.Type.HTTP

Networking Properties

socksProxy="hostname:port"

Configures a SOCKS proxy, and overrides any proxy configured with the http[s].proxy(Host|Port) system properties.

See also:

URL.openConnection(Proxy)

Proxy.Type.SOCKS

Networking Properties

Subelement Detail

Any FilterChain

If given, then the data that is added to the file is fed through this filter chain, and the task will complete only when the filter chain produces some output. This is useful to check if a specific line of text was appended to the file.

<url>

Designates the resource to access.

See also:

URL.openConnection()

The URL can be specified as a string and/or by syntactic components, as described in RFC 2396, section 3. The individual syntactic components take precendence or those in the string. If a component is neither configured individually, nor in the string, then default values take effect as documented below.

The following attributes and subelements are mutually exclusive:

context="..."

<context>

Text between start and end tag:

A textual definition of the URL. Individual components can be overridden with other attributes.

Attributes:

context="context-url"

The "base URL" for a relative URL (a simplified alternative for the <context> subelement described below) (defaults to none).

protocol="schema|http"

The "protocol" component of the URL.

host="host|localhost"

The "host" component of the URL.

port="port-number"

The "port" component of the URL. The default value Depends on the "protocol" component of the URL

userInfo="user-info"

The "userinfo" component of the URL, like "user [ ':'password]". Defaults to none.

path="path|/"

The "path" component of the URL. (An absolute path begins with a slash ("/"), a relative path doesn't.)

query="query-string"

The "query" component of the URL; is appended to the URL with a question mark ("?"). Can alternatively be configured through <formField> subelements.

ref="anchor"

The "ref" component (also known as "anchor" or "fragment identifier"). Defaults to none.

Subelements:

<formField>

These subelements are encoded and added to the query part of the URL as described in RFC 1866, section 8.2.2. An XML element that specifies a name-value pair.

Text between start and end tag:

The "value" text - may alternatively be configured by the "value="..."" attribute.

Attributes:

name="name"

The "name" of the name-value pair.

value="value"

The "value" text - may alternatively be configured by text nested between start and end tags.

<context>

Configures the "base URL" for a relative URL.

An alternative to context=...; must appear at most once.
(The configuration options for this element are the same as described above.)

<requestProperty>

Configures a "request property". (Request properties have different meanings for different protocols.)

See also:

URLConnection.addRequestProperty(String, String)

An XML element that specifies a name-value pair.

Text between start and end tag:

The "value" text - may alternatively be configured by the "value="..."" attribute.

Attributes:

name="name"

The "name" of the name-value pair.

value="value"

The "value" text - may alternatively be configured by text nested between start and end tags.