Class Indexer

java.lang.Object

org.springframework.expression.spel.ast.SpelNodeImpl

org.springframework.expression.spel.ast.Indexer

All Implemented Interfaces:

Opcodes, SpelNode

public class Indexer
extends SpelNodeImpl

An Indexer can index into some proceeding structure to access a particular element of the structure.

Numerical index values are zero-based, such as when accessing the n^th element of an array in Java.

Supported Structures

• Arrays: the n^th element
• Collections (lists, sets, etc.): the n^th element
• Strings: the n^th character as a String
• Maps: the value for the specified key
• Objects: the property with the specified name
• Custom Structures: via registered IndexAccessor implementations

Null-safe Indexing

As of Spring Framework 6.2, null-safe indexing is supported via the '?.' operator. For example, 'colors?.[0]' will evaluate to null if colors is null and will otherwise evaluate to the 0^th color. As of Spring Framework 7.0, null-safe indexing also applies when indexing into a structure contained in an Optional. For example, if colors is of type Optional<Colors>, the expression 'colors?.[0]' will evaluate to null if colors is null or empty and will otherwise evaluate to the 0^th color, effectively colors.get()[0].

Since:

3.0

Author:

Andy Clement, Phillip Webb, Stephane Nicoll, Sam Brannen

See Also:

• IndexAccessor
• CompilableIndexAccessor
• ReflectiveIndexAccessor

Field Summary

Fields inherited from class SpelNodeImpl

children, exitTypeDescriptor

Fields inherited from interface Opcodes

AALOAD, AASTORE, ACC_ABSTRACT, ACC_ANNOTATION, ACC_BRIDGE, ACC_DEPRECATED, ACC_ENUM, ACC_FINAL, ACC_INTERFACE, ACC_MANDATED, ACC_MODULE, ACC_NATIVE, ACC_OPEN, ACC_PRIVATE, ACC_PROTECTED, ACC_PUBLIC, ACC_RECORD, ACC_STATIC, ACC_STATIC_PHASE, ACC_STRICT, ACC_SUPER, ACC_SYNCHRONIZED, ACC_SYNTHETIC, ACC_TRANSIENT, ACC_TRANSITIVE, ACC_VARARGS, ACC_VOLATILE, ACONST_NULL, ALOAD, ANEWARRAY, ARETURN, ARRAYLENGTH, ASM10_EXPERIMENTAL, ASM4, ASM5, ASM6, ASM7, ASM8, ASM9, ASTORE, ATHROW, BALOAD, BASTORE, BIPUSH, CALOAD, CASTORE, CHECKCAST, D2F, D2I, D2L, DADD, DALOAD, DASTORE, DCMPG, DCMPL, DCONST_0, DCONST_1, DDIV, DLOAD, DMUL, DNEG, DOUBLE, DREM, DRETURN, DSTORE, DSUB, DUP, DUP_X1, DUP_X2, DUP2, DUP2_X1, DUP2_X2, F_APPEND, F_CHOP, F_FULL, F_NEW, F_SAME, F_SAME1, F2D, F2I, F2L, FADD, FALOAD, FASTORE, FCMPG, FCMPL, FCONST_0, FCONST_1, FCONST_2, FDIV, FLOAD, FLOAT, FMUL, FNEG, FREM, FRETURN, FSTORE, FSUB, GETFIELD, GETSTATIC, GOTO, H_GETFIELD, H_GETSTATIC, H_INVOKEINTERFACE, H_INVOKESPECIAL, H_INVOKESTATIC, H_INVOKEVIRTUAL, H_NEWINVOKESPECIAL, H_PUTFIELD, H_PUTSTATIC, I2B, I2C, I2D, I2F, I2L, I2S, IADD, IALOAD, IAND, IASTORE, ICONST_0, ICONST_1, ICONST_2, ICONST_3, ICONST_4, ICONST_5, ICONST_M1, IDIV, IF_ACMPEQ, IF_ACMPNE, IF_ICMPEQ, IF_ICMPGE, IF_ICMPGT, IF_ICMPLE, IF_ICMPLT, IF_ICMPNE, IFEQ, IFGE, IFGT, IFLE, IFLT, IFNE, IFNONNULL, IFNULL, IINC, ILOAD, IMUL, INEG, INSTANCEOF, INTEGER, INVOKEDYNAMIC, INVOKEINTERFACE, INVOKESPECIAL, INVOKESTATIC, INVOKEVIRTUAL, IOR, IREM, IRETURN, ISHL, ISHR, ISTORE, ISUB, IUSHR, IXOR, JSR, L2D, L2F, L2I, LADD, LALOAD, LAND, LASTORE, LCMP, LCONST_0, LCONST_1, LDC, LDIV, LLOAD, LMUL, LNEG, LONG, LOOKUPSWITCH, LOR, LREM, LRETURN, LSHL, LSHR, LSTORE, LSUB, LUSHR, LXOR, MONITORENTER, MONITOREXIT, MULTIANEWARRAY, NEW, NEWARRAY, NOP, NULL, POP, POP2, PUTFIELD, PUTSTATIC, RET, RETURN, SALOAD, SASTORE, SIPUSH, SOURCE_DEPRECATED, SOURCE_MASK, SWAP, T_BOOLEAN, T_BYTE, T_CHAR, T_DOUBLE, T_FLOAT, T_INT, T_LONG, T_SHORT, TABLESWITCH, TOP, UNINITIALIZED_THIS, V_PREVIEW, V1_1, V1_2, V1_3, V1_4, V1_5, V1_6, V1_7, V1_8, V10, V11, V12, V13, V14, V15, V16, V17, V18, V19, V20, V21, V22, V23, V24, V25, V9

Constructor Summary

Constructors

Constructor	Description
Indexer(boolean nullSafe, int startPos, int endPos, SpelNodeImpl indexExpression)	Create an Indexer with the given null-safe flag, start position, end position, and index expression.

Method Summary

Modifier and Type	Method	Description
void	generateCode(MethodVisitor mv, CodeFlow cf)	Generate the bytecode for this node into the supplied MethodVisitor.
TypedValue	getValueInternal(ExpressionState state)
protected ValueRef	getValueRef(ExpressionState state)
boolean	isCompilable()	Determine if this node can be compiled to bytecode.
final boolean	isNullSafe()	Does this node represent a null-safe index operation?
boolean	isWritable(ExpressionState expressionState)	Determine if this expression node will support a setValue() call.
TypedValue	setValueInternal(ExpressionState state, Supplier<TypedValue> valueSupplier)	Evaluate the expression to a node and then set the new value created by the specified Supplier on that node.
String	toStringAST()	Return the string form of this AST node.

Methods inherited from class SpelNodeImpl

generateCodeForArgument, generateCodeForArguments, generateCodeForArguments, getChild, getChildCount, getEndPosition, getExitDescriptor, getObjectClass, getStartPosition, getTypedValue, getValue, getValue, nextChildIs, setValue

Methods inherited from class Object

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

Constructor Details

Indexer

public Indexer(boolean nullSafe,
 int startPos,
 int endPos,
 SpelNodeImpl indexExpression)

Create an Indexer with the given null-safe flag, start position, end position, and index expression.

Since:

6.2

Method Details

isNullSafe

public final boolean isNullSafe()

Does this node represent a null-safe index operation?

Overrides:

isNullSafe in class SpelNodeImpl

Returns:

true if this node is the target of a null-safe operation

Since:

6.2

getValueInternal

public TypedValue getValueInternal(ExpressionState state)
                            throws EvaluationException

Specified by:

getValueInternal in class SpelNodeImpl

Throws:

EvaluationException

setValueInternal

public TypedValue setValueInternal(ExpressionState state,
 Supplier<TypedValue> valueSupplier)
                            throws EvaluationException

Description copied from class: SpelNodeImpl

Evaluate the expression to a node and then set the new value created by the specified Supplier on that node.

For example, if the expression evaluates to a property reference, then the property will be set to the new value.

Favor this method over SpelNodeImpl.setValue(ExpressionState, Object) when the value should be lazily computed.

By default, this method throws a SpelEvaluationException, effectively disabling this feature. Subclasses may override this method to provide an actual implementation.

Overrides:

setValueInternal in class SpelNodeImpl

Parameters:

state - the current expression state (includes the context)

valueSupplier - a supplier of the new value

Throws:

EvaluationException - if any problem occurs evaluating the expression or setting the new value

isWritable

public boolean isWritable(ExpressionState expressionState)
                   throws SpelEvaluationException

Description copied from interface: SpelNode

Determine if this expression node will support a setValue() call.

Specified by:

isWritable in interface SpelNode

Overrides:

isWritable in class SpelNodeImpl

Parameters:

expressionState - the current expression state (includes the context)

Returns:

true if the expression node will allow setValue()

Throws:

SpelEvaluationException

getValueRef

protected ValueRef getValueRef(ExpressionState state)
                        throws EvaluationException

Overrides:

getValueRef in class SpelNodeImpl

Throws:

EvaluationException

isCompilable

public boolean isCompilable()

Description copied from interface: SpelNode

Determine if this node can be compiled to bytecode.

The reasoning in each node may be different but will typically involve checking whether the exit type descriptor of the node is known and any relevant child nodes are compilable.

The default implementation returns false.

If you override this method, you must also override SpelNode.generateCode(MethodVisitor, CodeFlow).

Returns:

true if this node can be compiled to bytecode

See Also:

• SpelNode.generateCode(MethodVisitor, CodeFlow)

generateCode

public void generateCode(MethodVisitor mv,
 CodeFlow cf)

Description copied from interface: SpelNode

Generate the bytecode for this node into the supplied MethodVisitor.

Context information about the current expression being compiled is available in the supplied CodeFlow object — for example, information about the type of the object currently on the stack.

This method will not be invoked unless SpelNode.isCompilable() returns true.

The default implementation throws an IllegalStateException since SpelNode.isCompilable() returns false by default.

If you override this method, you must also override SpelNode.isCompilable().

Parameters:

mv - the ASM MethodVisitor into which code should be generated

cf - a context object with information about what is on the stack

See Also:

• SpelNode.isCompilable()

toStringAST

public String toStringAST()

Description copied from interface: SpelNode

Return the string form of this AST node.

Returns:

the string form