uk.ac.starlink.ttools.jel

Class JELUtils

java.lang.Object

uk.ac.starlink.ttools.jel.JELUtils

public class JELUtils
extends Object

This class provides some utility methods for use with the JEL expression compiler.

Since:

11 Feb 2005

Author:

Mark Taylor (Starlink)

Field Summary

Fields

Modifier and Type	Field and Description
static String	CLASSES_PROPERTY System property name for adding colon-separated list of additional classnames containing static methods.

Constructor Summary

Constructors

Constructor and Description
JELUtils()

Method Summary

Modifier and Type	Method and Description
static void	checkExpressionType(gnu.jel.Library lib, StarTable table, String expr, Class<?> clazz) Checks that an expression is legal and returns a particular class.
static gnu.jel.CompiledExpression	compile(gnu.jel.Library lib, StarTable table, String expr) Compiles an expression in the context of a given table.
static gnu.jel.CompiledExpression	compile(gnu.jel.Library lib, StarTable table, String expr, Class<?> clazz) Compiles an expression in the context of a given table with a required type for the result.
static gnu.jel.CompiledExpression[]	compileExpressions(StarTableJELRowReader reader, String[] exprs) Compiles a set of expressions relating to a table.
static JELQuantity	compileQuantity(gnu.jel.Library lib, StarTableJELRowReader jelRdr, String expr, Class<?> clazz) Compiles an expression in the context of a table reader to give a JELQuantity.
static java.util.function.Function<gnu.jel.Library,gnu.jel.CompiledExpression>	compiler(StarTable table, String expr, Class<?> clazz) Returns a function that can compile a fixed expression from a Library.
static JELRowReader	createDatalessRowReader(StarTable table) Returns a row reader that can be used for expression evaluation, optionally in the context of the non-data parts of a given context table.
static gnu.jel.Library	createLibrary(Class<?>[] staticLib, Class<?>[] dynamicLib, gnu.jel.DVMap resolver) Creates a JEL Library from basic information.
static Class<?>	getExpressionType(gnu.jel.Library lib, StarTable table, String expr) Gives the return type of an expression.
static gnu.jel.Library	getLibrary(JELRowReader reader) Returns a JEL Library suitable for expression evaluation within a table.
static List<Class<?>>	getStaticClasses() Returns the list of classes whose static methods will be mapped into the JEL evaluation namespace.
static Class<?>	getWrapperType(Class<?> clazz) Returns a non-primitive version of a given class.
static IOException	toIOException(gnu.jel.CompilationException e, String expr) Utility method to convert a CompilationException into an IOException.

Methods inherited from class java.lang.Object

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

Field Detail

CLASSES_PROPERTY

public static final String CLASSES_PROPERTY

System property name for adding colon-separated list of additional classnames containing static methods.

See Also:

Constant Field Values

Constructor Detail

JELUtils

public JELUtils()

Method Detail

getLibrary

public static gnu.jel.Library getLibrary(JELRowReader reader)

Returns a JEL Library suitable for expression evaluation within a table.

Parameters:

reader - object which can read rows from the table to be used for expression evaluation; may be null if there are no references to table-related expressions

Returns:

a JEL library

createLibrary

public static gnu.jel.Library createLibrary(Class<?>[] staticLib,
                                            Class<?>[] dynamicLib,
                                            gnu.jel.DVMap resolver)

Creates a JEL Library from basic information. This method should generally be used rather than the Library constructor, since it may apply additional customisation. Currently, it fixes static methods marked with the StateDependent annotation appropriately.

Parameters:

staticLib - array of classes whose public static methods are exported

dynamicLib - array of classes whose public methods are exported

resolver - object used to resolve names

Returns:

new library

See Also:

Library.Library(java.lang.Class<?>[], java.lang.Class<?>[], java.lang.Class<?>[], gnu.jel.DVMap, java.util.HashMap<java.lang.String, java.lang.Class<?>>)

createDatalessRowReader

public static JELRowReader createDatalessRowReader(StarTable table)

Returns a row reader that can be used for expression evaluation, optionally in the context of the non-data parts of a given context table. If the table is non-null, things like its parameters and row counts are available for reference. If the table is null, those things won't be available. In any case, references to table columns will not be recognised.

Parameters:

table - context table, or null

Returns:

row reader

getStaticClasses

public static List<Class<?>> getStaticClasses()

Returns the list of classes whose static methods will be mapped into the JEL evaluation namespace. This may be modified.

Returns:

list of classes with static methods

getExpressionType

public static Class<?> getExpressionType(gnu.jel.Library lib,
                                         StarTable table,
                                         String expr)
                                  throws gnu.jel.CompilationException

Gives the return type of an expression. This also has the effect of testing that an expression is legal.

Parameters:

lib - JEL library

table - context table

expr - string representation of the expression

Returns:

class which evaluation of expr using lib will return

Throws:

gnu.jel.CompilationException - if expr cannot be compiled

checkExpressionType

public static void checkExpressionType(gnu.jel.Library lib,
                                       StarTable table,
                                       String expr,
                                       Class<?> clazz)
                                throws gnu.jel.CompilationException

Checks that an expression is legal and returns a particular class.

Parameters:

lib - JEL library

table - context table

expr - string representation of the expression

clazz - return type required from expr

Throws:

gnu.jel.CompilationException - if expr cannot be compiled or will return a type other than clazz (or one of its subtypes)

compile

public static gnu.jel.CompiledExpression compile(gnu.jel.Library lib,
                                                 StarTable table,
                                                 String expr,
                                                 Class<?> clazz)
                                          throws gnu.jel.CompilationException

Compiles an expression in the context of a given table with a required type for the result. Additional to the behaviour of Evaluator.compile this also checks for expressions which exactly match table column names, even if they are not syntactically legal identifiers.

Parameters:

lib - JEL library

table - context table

expr - expression string

clazz - required class of resulting expression

Returns:

compiled expression

Throws:

gnu.jel.CompilationException

compile

public static gnu.jel.CompiledExpression compile(gnu.jel.Library lib,
                                                 StarTable table,
                                                 String expr)
                                          throws gnu.jel.CompilationException

Compiles an expression in the context of a given table. Additional to the behaviour of Evaluator.compile this also checks for expressions which exactly match table column names, even if they are not syntactically legal identifiers.

Parameters:

lib - JEL library

table - context table

expr - expression string

Returns:

compiled expression

Throws:

gnu.jel.CompilationException

compileQuantity

public static JELQuantity compileQuantity(gnu.jel.Library lib,
                                          StarTableJELRowReader jelRdr,
                                          String expr,
                                          Class<?> clazz)
                                   throws gnu.jel.CompilationException

Compiles an expression in the context of a table reader to give a JELQuantity. This does the same job as the compile methods, but it provides additional metadata if it can be retrieved from the table context.

Parameters:

lib - JEL library

jelRdr - context table reader

expr - expression string

clazz - required return type of compiled expression, or null if no requirement

Returns:

compiled quantity

Throws:

gnu.jel.CompilationException

compiler

public static java.util.function.Function<gnu.jel.Library,gnu.jel.CompiledExpression> compiler(StarTable table,
                                                                                               String expr,
                                                                                               Class<?> clazz)
                                                                                        throws gnu.jel.CompilationException

Returns a function that can compile a fixed expression from a Library. This method does a test compilation before it returns, so that if there's something wrong with the expression this method will throw a CompilationException, but invocations of the returned Function on Libraries compatible with the supplied table ought not to. The returned function therefore does not need to declare throwing a CompilerException. If for some reason the deferred compilations do fail, a RuntimeException is returned.

Parameters:

table - table from which libraries will be derived

expr - expression to compile

clazz - required result type of expression, or null for automatic

Throws:

gnu.jel.CompilationException

compileExpressions

public static gnu.jel.CompiledExpression[] compileExpressions(StarTableJELRowReader reader,
                                                              String[] exprs)
                                                       throws IOException

Compiles a set of expressions relating to a table.

Any CompilationExceptions are rethrown as IOExceptions; this method should therefore generally be used only if the expressions are expected to be free from errors (have been compiled before).

Parameters:

reader - table reader

exprs - strings giving JEL expressions to be compiled

Returns:

array with one compiled expression for each input string

Throws:

IOException - in case of any CompilationException

toIOException

public static IOException toIOException(gnu.jel.CompilationException e,
                                        String expr)

Utility method to convert a CompilationException into an IOException.

Parameters:

e - compilation exception

expr - expression for which compilation failed, to be reported in error message

getWrapperType

public static Class<?> getWrapperType(Class<?> clazz)

Returns a non-primitive version of a given class. If clazz is a non-primitive type, it will be returned, otherwise the wrapper class corresponding to the primitive type of clazz will be returned (e.g. Integer for int).

Parameters:

clazz - input class

Returns:

non-primitive class matching clazz