uk.ac.starlink.util

Class BeanConfig

java.lang.Object

uk.ac.starlink.util.BeanConfig

public class BeanConfig
extends java.lang.Object

Utility class for configuring dynamically loaded objects.

The idea is that objects can be configured from user-supplied text strings that configure bean-like properties. For instance an object may be specified on the command line or using a system property with a syntax like:

    "java.util.Date(year=212,day=1)"
 

which would construct a Date object using its no-arg constructor, and then configure the bean-like "year" property by reflectively invoking the setYear and setDay methods of the Date class.

Where present, a ConfigMethod annotation on the relevant mutator methods is used to provide aliased property names, as well as to improve LoadException error messages when property setting fails.

The configuration syntax is fairly straightforward; the format is a comma-separated list of name=value settings within a pair of parentheses. Obvious serializations are supported for numeric and boolean values; string values are unquoted; commas may be backslash-escaped; and symbolic values are permitted for Enums and static public members on the value class or created object class.

Since:

11 Sep 2020

See Also:

ConfigMethod

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	BeanConfig.Setting Represents an object configuration operation.

Constructor Summary

Constructors

Constructor and Description
BeanConfig(java.lang.String baseTxt, java.lang.String configTxt) Constructs a BeanConfig with a basic object representation and a string providing configuration information.

Method Summary

Modifier and Type	Method and Description
static void	applySetting(java.lang.Object target, BeanConfig.Setting setting) Applies a given setting to an object.
void	configBean(java.lang.Object target) Attempts to apply this object's configuration setttings to a supplied target object.
java.lang.String	getBaseText() Returns the basic object name for this object.
java.lang.String	getConfigText() Returns configuration specification.
static java.lang.String	getMethodUsage(java.lang.reflect.Method configMethod) Returns a usage string corresponding to a given configuration method.
BeanConfig.Setting[]	getSettings() Returns the parsed settings for this object, as extracted from the configuration text.
static void	main(java.lang.String[] args)
static BeanConfig	parseSpec(java.lang.String txt) Parses an object specification to produce a BeanConfig instance.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BeanConfig

public BeanConfig(java.lang.String baseTxt,
                  java.lang.String configTxt)

Constructs a BeanConfig with a basic object representation and a string providing configuration information. The baseTxt could be a classname or something else. The configTxt should normally be of the form name1=value1,name2=value2,...; if other forms are used, a LoadException with a helpful error message will be generated as appropriate by relevant method invocations.

Parameters:

baseTxt - basic object name or representation

configTxt - configuration text, normally as supplied in trailing parenthesis

Method Detail

getBaseText

public java.lang.String getBaseText()

Returns the basic object name for this object. May be a classname or something else. This should not be null.

Returns:

basic representation

getConfigText

public java.lang.String getConfigText()

Returns configuration specification. May be null if there was no trailing parenthesis.

Returns:

configuration text, nominally of the form "n1=v1,n2=v2,...",

getSettings

public BeanConfig.Setting[] getSettings()
                                 throws LoadException

Returns the parsed settings for this object, as extracted from the configuration text. The list may be empty.

Returns:

configuration settings

Throws:

LoadException - if the config text was badly-formed

configBean

public void configBean(java.lang.Object target)
                throws LoadException

Attempts to apply this object's configuration setttings to a supplied target object.

Parameters:

target - object to configure

Throws:

LoadException - with a helpful error message if the settings don't work

parseSpec

public static BeanConfig parseSpec(java.lang.String txt)

Parses an object specification to produce a BeanConfig instance. The specification is of the form base-name(n1=v1,n2=v2,...). If there is no well-formed parenthesised config-string at the end, the returned object has a base-name that is the whole of the input string, and no config text.

Parameters:

txt - input text

Returns:

BaseConfig object, which may or may not have configuration information

applySetting

public static void applySetting(java.lang.Object target,
                                BeanConfig.Setting setting)
                         throws java.lang.ReflectiveOperationException

Applies a given setting to an object.

Parameters:

target - object to configure

setting - setting to apply

Throws:

java.lang.RuntimeException - in case of various problems with converting the supplied string to the required type

java.lang.ReflectiveOperationException - in case of some reflection trouble

getMethodUsage

public static java.lang.String getMethodUsage(java.lang.reflect.Method configMethod)

Returns a usage string corresponding to a given configuration method.

Parameters:

configMethod - mutator method

Returns:

short user-directed usage text

main

public static void main(java.lang.String[] args)
                 throws java.lang.ReflectiveOperationException,
                        LoadException

Throws:

java.lang.ReflectiveOperationException

LoadException