uk.ac.starlink.table.ClassTableScheme Maven / Gradle / Ivy
package uk.ac.starlink.table;
import java.io.IOException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
/**
* TableScheme implementation that allows to use any TableScheme
* implementation on the classpath.
*
* Usage is for example:
*
* class:uk.ac.starlink.table.LoopTableScheme:10
*
*
* @author Mark Taylor
* @since 22 Jul 2020
*/
public class ClassTableScheme implements TableScheme, Documented {
private static final Pattern CLASSNAME_REGEX =
Pattern.compile( "([\\p{L}[0-9]_$.]+):(.*)" );
/**
* Returns "class";
*/
public String getSchemeName() {
return "class";
}
public String getSchemeUsage() {
return ":";
}
public String getExampleSpecification() {
return LoopTableScheme.class.getName() + ":" + 5;
}
public String getXmlDescription() {
String prefix = ":" + getSchemeName() + ":";
String exClassname = LoopTableScheme.class.getName();
String exArglist = "10";
return String.join( "\n",
"Uses an instance of a named class that implements",
"the uk.ac.starlink.table.TableScheme interface",
"and that has a no-arg constructor.",
"Arguments to be passed to an instance of the named class",
"are appended after a colon following the classname.",
"
",
"For example, the specification",
"\"" + prefix + exClassname + ":" + exArglist + "\"",
"would return a table constructed by the code",
"new " + exClassname + "()"
+ ".createTable(\"" + exArglist +"\").",
"
",
"" );
}
public StarTable createTable( String spec ) throws IOException {
Matcher matcher = CLASSNAME_REGEX.matcher( spec );
if ( ! matcher.matches() ) {
throw new TableFormatException();
}
String classname = matcher.group( 1 );
String subspec = matcher.group( 2 );
Class clazz;
try {
clazz = Class.forName( classname );
}
catch ( ClassNotFoundException e ) {
throw new TableFormatException( "Unkown class " + classname );
}
if ( ! TableScheme.class.isAssignableFrom( clazz ) ) {
throw new TableFormatException( "Class " + classname
+ " does not implement "
+ TableScheme.class.getName() );
}
@SuppressWarnings("unchecked")
Class schemeClazz =
(Class) clazz;
TableScheme subscheme;
try {
subscheme = schemeClazz.newInstance();
}
catch ( InstantiationException | IllegalAccessException e ) {
throw new TableFormatException( "Can't instantiate "
+ clazz.getName(), e );
}
return subscheme.createTable( subspec );
}
}