https://github.com/spring-projects/spring-framework: Spring Expression Language (SpEL) (Spring IO)
  • Juergen Hoeller 
/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.expression.spel;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.List;

import org.springframework.asm.ClassWriter;
import org.springframework.asm.MethodVisitor;
import org.springframework.asm.Opcodes;
import org.springframework.lang.Nullable;
import org.springframework.util.CollectionUtils;


Manages the class being generated by the compilation process.

Records intermediate compilation state as the bytecode is generated.
Also includes various bytecode generation helper functions.

Author:Andy Clement, Juergen Hoeller
Since:4.1
/**
 * Manages the class being generated by the compilation process.
 *
 * <p>Records intermediate compilation state as the bytecode is generated.
 * Also includes various bytecode generation helper functions.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 4.1
 */
public class CodeFlow implements Opcodes {

	
Name of the class being generated. Typically used when generating code
that accesses freshly generated fields on the generated type.

/**
	 * Name of the class being generated. Typically used when generating code
	 * that accesses freshly generated fields on the generated type.
	 */
	private final String className;

	
The current class being generated.

/**
	 * The current class being generated.
	 */
	private final ClassWriter classWriter;

	
Record the type of what is on top of the bytecode stack (i.e. the type of the
output from the previous expression component). New scopes are used to evaluate
sub-expressions like the expressions for the argument values in a method invocation
expression.

/**
	 * Record the type of what is on top of the bytecode stack (i.e. the type of the
	 * output from the previous expression component). New scopes are used to evaluate
	 * sub-expressions like the expressions for the argument values in a method invocation
	 * expression.
	 */
	private final Deque<List<String>> compilationScopes;

	
As SpEL ast nodes are called to generate code for the main evaluation method
they can register to add a field to this class. Any registered FieldAdders
will be called after the main evaluation function has finished being generated.

/**
	 * As SpEL ast nodes are called to generate code for the main evaluation method
	 * they can register to add a field to this class. Any registered FieldAdders
	 * will be called after the main evaluation function has finished being generated.
	 */
	@Nullable
	private List<FieldAdder> fieldAdders;

	
As SpEL ast nodes are called to generate code for the main evaluation method
they can register to add code to a static initializer in the class. Any
registered ClinitAdders will be called after the main evaluation function
has finished being generated.

/**
	 * As SpEL ast nodes are called to generate code for the main evaluation method
	 * they can register to add code to a static initializer in the class. Any
	 * registered ClinitAdders will be called after the main evaluation function
	 * has finished being generated.
	 */
	@Nullable
	private List<ClinitAdder> clinitAdders;

	
When code generation requires holding a value in a class level field, this
is used to track the next available field id (used as a name suffix).

/**
	 * When code generation requires holding a value in a class level field, this
	 * is used to track the next available field id (used as a name suffix).
	 */
	private int nextFieldId = 1;

	
When code generation requires an intermediate variable within a method,
this method records the next available variable (variable 0 is 'this').

/**
	 * When code generation requires an intermediate variable within a method,
	 * this method records the next available variable (variable 0 is 'this').
	 */
	private int nextFreeVariableId = 1;


	
Construct a new CodeFlow for the given class. 
Params:
  • className – the name of the class
  • classWriter – the corresponding ASM ClassWriter
/**
	 * Construct a new {@code CodeFlow} for the given class.
	 * @param className the name of the class
	 * @param classWriter the corresponding ASM {@code ClassWriter}
	 */
	public CodeFlow(String className, ClassWriter classWriter) {
		this.className = className;
		this.classWriter = classWriter;
		this.compilationScopes = new ArrayDeque<>();
		this.compilationScopes.add(new ArrayList<String>());
	}


	
Push the byte code to load the target (i.e. what was passed as the first argument
to CompiledExpression.getValue(target, context))

Params:
  • mv – the visitor into which the load instruction should be inserted
/**
	 * Push the byte code to load the target (i.e. what was passed as the first argument
	 * to CompiledExpression.getValue(target, context))
	 * @param mv the visitor into which the load instruction should be inserted
	 */
	public void loadTarget(MethodVisitor mv) {
		mv.visitVarInsn(ALOAD, 1);
	}

	
Push the bytecode to load the EvaluationContext (the second parameter passed to
the compiled expression method).

Params:
  • mv – the visitor into which the load instruction should be inserted
Since:4.3.4
/**
	 * Push the bytecode to load the EvaluationContext (the second parameter passed to
	 * the compiled expression method).
	 * @param mv the visitor into which the load instruction should be inserted
	 * @since 4.3.4
	 */
	public void loadEvaluationContext(MethodVisitor mv) {
		mv.visitVarInsn(ALOAD, 2);
	}

	
Record the descriptor for the most recently evaluated expression element.

Params:
  • descriptor – type descriptor for most recently evaluated element
/**
	 * Record the descriptor for the most recently evaluated expression element.
	 * @param descriptor type descriptor for most recently evaluated element
	 */
	public void pushDescriptor(@Nullable String descriptor) {
		if (descriptor != null) {
			this.compilationScopes.element().add(descriptor);
		}
	}

	
Enter a new compilation scope, usually due to nested expression evaluation. For
example when the arguments for a method invocation expression are being evaluated,
each argument will be evaluated in a new scope.

/**
	 * Enter a new compilation scope, usually due to nested expression evaluation. For
	 * example when the arguments for a method invocation expression are being evaluated,
	 * each argument will be evaluated in a new scope.
	 */
	public void enterCompilationScope() {
		this.compilationScopes.push(new ArrayList<>());
	}

	
Exit a compilation scope, usually after a nested expression has been evaluated. For
example after an argument for a method invocation has been evaluated this method
returns us to the previous (outer) scope.

/**
	 * Exit a compilation scope, usually after a nested expression has been evaluated. For
	 * example after an argument for a method invocation has been evaluated this method
	 * returns us to the previous (outer) scope.
	 */
	public void exitCompilationScope() {
		this.compilationScopes.pop();
	}

	
Return the descriptor for the item currently on top of the stack (in the current scope).

/**
	 * Return the descriptor for the item currently on top of the stack (in the current scope).
	 */
	@Nullable
	public String lastDescriptor() {
		return CollectionUtils.lastElement(this.compilationScopes.peek());
	}

	
If the codeflow shows the last expression evaluated to java.lang.Boolean then
insert the necessary instructions to unbox that to a boolean primitive.

Params:
  • mv – the visitor into which new instructions should be inserted
/**
	 * If the codeflow shows the last expression evaluated to java.lang.Boolean then
	 * insert the necessary instructions to unbox that to a boolean primitive.
	 * @param mv the visitor into which new instructions should be inserted
	 */
	public void unboxBooleanIfNecessary(MethodVisitor mv) {
		if ("Ljava/lang/Boolean".equals(lastDescriptor())) {
			mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Boolean", "booleanValue", "()Z", false);
		}
	}

	
Called after the main expression evaluation method has been generated, this
method will callback any registered FieldAdders or ClinitAdders to add any
extra information to the class representing the compiled expression.

/**
	 * Called after the main expression evaluation method has been generated, this
	 * method will callback any registered FieldAdders or ClinitAdders to add any
	 * extra information to the class representing the compiled expression.
	 */
	public void finish() {
		if (this.fieldAdders != null) {
			for (FieldAdder fieldAdder : this.fieldAdders) {
				fieldAdder.generateField(this.classWriter, this);
			}
		}
		if (this.clinitAdders != null) {
			MethodVisitor mv = this.classWriter.visitMethod(ACC_PUBLIC | ACC_STATIC, "<clinit>", "()V", null, null);
			mv.visitCode();
			this.nextFreeVariableId = 0;  // to 0 because there is no 'this' in a clinit
			for (ClinitAdder clinitAdder : this.clinitAdders) {
				clinitAdder.generateCode(mv, this);
			}
			mv.visitInsn(RETURN);
			mv.visitMaxs(0,0);  // not supplied due to COMPUTE_MAXS
			mv.visitEnd();
		}
	}

	
Register a FieldAdder which will add a new field to the generated
class to support the code produced by an ast nodes primary
generateCode() method.

/**
	 * Register a FieldAdder which will add a new field to the generated
	 * class to support the code produced by an ast nodes primary
	 * generateCode() method.
	 */
	public void registerNewField(FieldAdder fieldAdder) {
		if (this.fieldAdders == null) {
			this.fieldAdders = new ArrayList<>();
		}
		this.fieldAdders.add(fieldAdder);
	}

	
Register a ClinitAdder which will add code to the static
initializer in the generated class to support the code
produced by an ast nodes primary generateCode() method.

/**
	 * Register a ClinitAdder which will add code to the static
	 * initializer in the generated class to support the code
	 * produced by an ast nodes primary generateCode() method.
	 */
	public void registerNewClinit(ClinitAdder clinitAdder) {
		if (this.clinitAdders == null) {
			this.clinitAdders = new ArrayList<>();
		}
		this.clinitAdders.add(clinitAdder);
	}

	public int nextFieldId() {
		return this.nextFieldId++;
	}

	public int nextFreeVariableId() {
		return this.nextFreeVariableId++;
	}

	public String getClassName() {
		return this.className;
	}


	
Insert any necessary cast and value call to convert from a boxed type to a
primitive value.

Params:
  • mv – the method visitor into which instructions should be inserted
  • ch – the primitive type desired as output
  • stackDescriptor – the descriptor of the type on top of the stack
/**
	 * Insert any necessary cast and value call to convert from a boxed type to a
	 * primitive value.
	 * @param mv the method visitor into which instructions should be inserted
	 * @param ch the primitive type desired as output
	 * @param stackDescriptor the descriptor of the type on top of the stack
	 */
	public static void insertUnboxInsns(MethodVisitor mv, char ch, @Nullable String stackDescriptor) {
		if (stackDescriptor == null) {
			return;
		}
		switch (ch) {
			case 'Z':
				if (!stackDescriptor.equals("Ljava/lang/Boolean")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Boolean");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Boolean", "booleanValue", "()Z", false);
				break;
			case 'B':
				if (!stackDescriptor.equals("Ljava/lang/Byte")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Byte");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Byte", "byteValue", "()B", false);
				break;
			case 'C':
				if (!stackDescriptor.equals("Ljava/lang/Character")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Character");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Character", "charValue", "()C", false);
				break;
			case 'D':
				if (!stackDescriptor.equals("Ljava/lang/Double")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Double");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Double", "doubleValue", "()D", false);
				break;
			case 'F':
				if (!stackDescriptor.equals("Ljava/lang/Float")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Float");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Float", "floatValue", "()F", false);
				break;
			case 'I':
				if (!stackDescriptor.equals("Ljava/lang/Integer")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Integer");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Integer", "intValue", "()I", false);
				break;
			case 'J':
				if (!stackDescriptor.equals("Ljava/lang/Long")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Long");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Long", "longValue", "()J", false);
				break;
			case 'S':
				if (!stackDescriptor.equals("Ljava/lang/Short")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Short");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Short", "shortValue", "()S", false);
				break;
			default:
				throw new IllegalArgumentException("Unboxing should not be attempted for descriptor '" + ch + "'");
		}
	}

	
For numbers, use the appropriate method on the number to convert it to the primitive type requested.

Params:
  • mv – the method visitor into which instructions should be inserted
  • targetDescriptor – the primitive type desired as output
  • stackDescriptor – the descriptor of the type on top of the stack
/**
	 * For numbers, use the appropriate method on the number to convert it to the primitive type requested.
	 * @param mv the method visitor into which instructions should be inserted
	 * @param targetDescriptor the primitive type desired as output
	 * @param stackDescriptor the descriptor of the type on top of the stack
	 */
	public static void insertUnboxNumberInsns(
			MethodVisitor mv, char targetDescriptor, @Nullable String stackDescriptor) {

		if (stackDescriptor == null) {
			return;
		}

		switch (targetDescriptor) {
			case 'D':
				if (stackDescriptor.equals("Ljava/lang/Object")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Number");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Number", "doubleValue", "()D", false);
				break;
			case 'F':
				if (stackDescriptor.equals("Ljava/lang/Object")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Number");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Number", "floatValue", "()F", false);
				break;
			case 'J':
				if (stackDescriptor.equals("Ljava/lang/Object")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Number");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Number", "longValue", "()J", false);
				break;
			case 'I':
				if (stackDescriptor.equals("Ljava/lang/Object")) {
					mv.visitTypeInsn(CHECKCAST, "java/lang/Number");
				}
				mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Number", "intValue", "()I", false);
				break;
			// does not handle Z, B, C, S
			default:
				throw new IllegalArgumentException("Unboxing should not be attempted for descriptor '" + targetDescriptor + "'");
		}
	}

	
Insert any necessary numeric conversion bytecodes based upon what is on the stack and the desired target type.

Params:
  • mv – the method visitor into which instructions should be placed
  • targetDescriptor – the (primitive) descriptor of the target type
  • stackDescriptor – the descriptor of the operand on top of the stack
/**
	 * Insert any necessary numeric conversion bytecodes based upon what is on the stack and the desired target type.
	 * @param mv the method visitor into which instructions should be placed
	 * @param targetDescriptor the (primitive) descriptor of the target type
	 * @param stackDescriptor the descriptor of the operand on top of the stack
	 */
	public static void insertAnyNecessaryTypeConversionBytecodes(MethodVisitor mv, char targetDescriptor, String stackDescriptor) {
		if (CodeFlow.isPrimitive(stackDescriptor)) {
			char stackTop = stackDescriptor.charAt(0);
			if (stackTop == 'I' || stackTop == 'B' || stackTop == 'S' || stackTop == 'C') {
				if (targetDescriptor == 'D') {
					mv.visitInsn(I2D);
				}
				else if (targetDescriptor == 'F') {
					mv.visitInsn(I2F);
				}
				else if (targetDescriptor == 'J') {
					mv.visitInsn(I2L);
				}
				else if (targetDescriptor == 'I') {
					// nop
				}
				else {
					throw new IllegalStateException("Cannot get from " + stackTop + " to " + targetDescriptor);
				}
			}
			else if (stackTop == 'J') {
				if (targetDescriptor == 'D') {
					mv.visitInsn(L2D);
				}
				else if (targetDescriptor == 'F') {
					mv.visitInsn(L2F);
				}
				else if (targetDescriptor == 'J') {
					// nop
				}
				else if (targetDescriptor == 'I') {
					mv.visitInsn(L2I);
				}
				else {
					throw new IllegalStateException("Cannot get from " + stackTop + " to " + targetDescriptor);
				}
			}
			else if (stackTop == 'F') {
				if (targetDescriptor == 'D') {
					mv.visitInsn(F2D);
				}
				else if (targetDescriptor == 'F') {
					// nop
				}
				else if (targetDescriptor == 'J') {
					mv.visitInsn(F2L);
				}
				else if (targetDescriptor == 'I') {
					mv.visitInsn(F2I);
				}
				else {
					throw new IllegalStateException("Cannot get from " + stackTop + " to " + targetDescriptor);
				}
			}
			else if (stackTop == 'D') {
				if (targetDescriptor == 'D') {
					// nop
				}
				else if (targetDescriptor == 'F') {
					mv.visitInsn(D2F);
				}
				else if (targetDescriptor == 'J') {
					mv.visitInsn(D2L);
				}
				else if (targetDescriptor == 'I') {
					mv.visitInsn(D2I);
				}
				else {
					throw new IllegalStateException("Cannot get from " + stackDescriptor + " to " + targetDescriptor);
				}
			}
		}
	}


	
Create the JVM signature descriptor for a method. This consists of the descriptors
for the method parameters surrounded with parentheses, followed by the
descriptor for the return type. Note the descriptors here are JVM descriptors,
unlike the other descriptor forms the compiler is using which do not include the
trailing semicolon.

Params:
  • method – the method
Returns:a String signature descriptor (e.g. "(ILjava/lang/String;)V")
/**
	 * Create the JVM signature descriptor for a method. This consists of the descriptors
	 * for the method parameters surrounded with parentheses, followed by the
	 * descriptor for the return type. Note the descriptors here are JVM descriptors,
	 * unlike the other descriptor forms the compiler is using which do not include the
	 * trailing semicolon.
	 * @param method the method
	 * @return a String signature descriptor (e.g. "(ILjava/lang/String;)V")
	 */
	public static String createSignatureDescriptor(Method method) {
		Class<?>[] params = method.getParameterTypes();
		StringBuilder sb = new StringBuilder();
		sb.append("(");
		for (Class<?> param : params) {
			sb.append(toJvmDescriptor(param));
		}
		sb.append(")");
		sb.append(toJvmDescriptor(method.getReturnType()));
		return sb.toString();
	}

	
Create the JVM signature descriptor for a constructor. This consists of the
descriptors for the constructor parameters surrounded with parentheses, followed by
the descriptor for the return type, which is always "V". Note the
descriptors here are JVM descriptors, unlike the other descriptor forms the
compiler is using which do not include the trailing semicolon.

Params:
  • ctor – the constructor
Returns:a String signature descriptor (e.g. "(ILjava/lang/String;)V")
/**
	 * Create the JVM signature descriptor for a constructor. This consists of the
	 * descriptors for the constructor parameters surrounded with parentheses, followed by
	 * the descriptor for the return type, which is always "V". Note the
	 * descriptors here are JVM descriptors, unlike the other descriptor forms the
	 * compiler is using which do not include the trailing semicolon.
	 * @param ctor the constructor
	 * @return a String signature descriptor (e.g. "(ILjava/lang/String;)V")
	 */
	public static String createSignatureDescriptor(Constructor<?> ctor) {
		Class<?>[] params = ctor.getParameterTypes();
		StringBuilder sb = new StringBuilder();
		sb.append("(");
		for (Class<?> param : params) {
			sb.append(toJvmDescriptor(param));
		}
		sb.append(")V");
		return sb.toString();
	}

	
Determine the JVM descriptor for a specified class. Unlike the other descriptors
used in the compilation process, this is the one the JVM wants, so this one
includes any necessary trailing semicolon (e.g. Ljava/lang/String; rather than
Ljava/lang/String)

Params:
  • clazz – a class
Returns:the JVM descriptor for the class
/**
	 * Determine the JVM descriptor for a specified class. Unlike the other descriptors
	 * used in the compilation process, this is the one the JVM wants, so this one
	 * includes any necessary trailing semicolon (e.g. Ljava/lang/String; rather than
	 * Ljava/lang/String)
	 * @param clazz a class
	 * @return the JVM descriptor for the class
	 */
	public static String toJvmDescriptor(Class<?> clazz) {
		StringBuilder sb = new StringBuilder();
		if (clazz.isArray()) {
			while (clazz.isArray()) {
				sb.append("[");
				clazz = clazz.getComponentType();
			}
		}
		if (clazz.isPrimitive()) {
			if (clazz == Boolean.TYPE) {
				sb.append('Z');
			}
			else if (clazz == Byte.TYPE) {
				sb.append('B');
			}
			else if (clazz == Character.TYPE) {
				sb.append('C');
			}
			else if (clazz == Double.TYPE) {
				sb.append('D');
			}
			else if (clazz == Float.TYPE) {
				sb.append('F');
			}
			else if (clazz == Integer.TYPE) {
				sb.append('I');
			}
			else if (clazz == Long.TYPE) {
				sb.append('J');
			}
			else if (clazz == Short.TYPE) {
				sb.append('S');
			}
			else if (clazz == Void.TYPE) {
				sb.append('V');
			}
		}
		else {
			sb.append("L");
			sb.append(clazz.getName().replace('.', '/'));
			sb.append(";");
		}
		return sb.toString();
	}

	
Determine the descriptor for an object instance (or null). 
Params:
  • value – an object (possibly null)
Returns:the type descriptor for the object (descriptor is "Ljava/lang/Object" for null value)
/**
	 * Determine the descriptor for an object instance (or {@code null}).
	 * @param value an object (possibly {@code null})
	 * @return the type descriptor for the object
	 * (descriptor is "Ljava/lang/Object" for {@code null} value)
	 */
	public static String toDescriptorFromObject(@Nullable Object value) {
		if (value == null) {
			return "Ljava/lang/Object";
		}
		else {
			return toDescriptor(value.getClass());
		}
	}

	
Determine whether the descriptor is for a boolean primitive or boolean reference type.

Params:
  • descriptor – type descriptor
Returns:true if the descriptor is boolean compatible
/**
	 * Determine whether the descriptor is for a boolean primitive or boolean reference type.
	 * @param descriptor type descriptor
	 * @return {@code true} if the descriptor is boolean compatible
	 */
	public static boolean isBooleanCompatible(@Nullable String descriptor) {
		return (descriptor != null && (descriptor.equals("Z") || descriptor.equals("Ljava/lang/Boolean")));
	}

	
Determine whether the descriptor is for a primitive type.

Params:
  • descriptor – type descriptor
Returns:true if a primitive type
/**
	 * Determine whether the descriptor is for a primitive type.
	 * @param descriptor type descriptor
	 * @return {@code true} if a primitive type
	 */
	public static boolean isPrimitive(@Nullable String descriptor) {
		return (descriptor != null && descriptor.length() == 1);
	}

	
Determine whether the descriptor is for a primitive array (e.g. "[[I").

Params:
  • descriptor – the descriptor for a possible primitive array
Returns:true if the descriptor a primitive array
/**
	 * Determine whether the descriptor is for a primitive array (e.g. "[[I").
	 * @param descriptor the descriptor for a possible primitive array
	 * @return {@code true} if the descriptor a primitive array
	 */
	public static boolean isPrimitiveArray(@Nullable String descriptor) {
		if (descriptor == null) {
			return false;
		}
		boolean primitive = true;
		for (int i = 0, max = descriptor.length(); i < max; i++) {
			char ch = descriptor.charAt(i);
			if (ch == '[') {
				continue;
			}
			primitive = (ch != 'L');
			break;
		}
		return primitive;
	}

	
Determine whether boxing/unboxing can get from one type to the other.
Assumes at least one of the types is in boxed form (i.e. single char descriptor).

Returns:true if it is possible to get (via boxing) from one descriptor to the other
/**
	 * Determine whether boxing/unboxing can get from one type to the other.
	 * Assumes at least one of the types is in boxed form (i.e. single char descriptor).
	 * @return {@code true} if it is possible to get (via boxing) from one descriptor to the other
	 */
	public static boolean areBoxingCompatible(String desc1, String desc2) {
		if (desc1.equals(desc2)) {
			return true;
		}
		if (desc1.length() == 1) {
			if (desc1.equals("Z")) {
				return desc2.equals("Ljava/lang/Boolean");
			}
			else if (desc1.equals("D")) {
				return desc2.equals("Ljava/lang/Double");
			}
			else if (desc1.equals("F")) {
				return desc2.equals("Ljava/lang/Float");
			}
			else if (desc1.equals("I")) {
				return desc2.equals("Ljava/lang/Integer");
			}
			else if (desc1.equals("J")) {
				return desc2.equals("Ljava/lang/Long");
			}
		}
		else if (desc2.length() == 1) {
			if (desc2.equals("Z")) {
				return desc1.equals("Ljava/lang/Boolean");
			}
			else if (desc2.equals("D")) {
				return desc1.equals("Ljava/lang/Double");
			}
			else if (desc2.equals("F")) {
				return desc1.equals("Ljava/lang/Float");
			}
			else if (desc2.equals("I")) {
				return desc1.equals("Ljava/lang/Integer");
			}
			else if (desc2.equals("J")) {
				return desc1.equals("Ljava/lang/Long");
			}
		}
		return false;
	}

	
Determine if the supplied descriptor is for a supported number type or boolean. The
compilation process only (currently) supports certain number types. These are
double, float, long and int.

Params:
  • descriptor – the descriptor for a type
Returns:true if the descriptor is for a supported numeric type or boolean
/**
	 * Determine if the supplied descriptor is for a supported number type or boolean. The
	 * compilation process only (currently) supports certain number types. These are
	 * double, float, long and int.
	 * @param descriptor the descriptor for a type
	 * @return {@code true} if the descriptor is for a supported numeric type or boolean
	 */
	public static boolean isPrimitiveOrUnboxableSupportedNumberOrBoolean(@Nullable String descriptor) {
		if (descriptor == null) {
			return false;
		}
		if (isPrimitiveOrUnboxableSupportedNumber(descriptor)) {
			return true;
		}
		return ("Z".equals(descriptor) || descriptor.equals("Ljava/lang/Boolean"));
	}

	
Determine if the supplied descriptor is for a supported number. The compilation
process only (currently) supports certain number types. These are double, float,
long and int.

Params:
  • descriptor – the descriptor for a type
Returns:true if the descriptor is for a supported numeric type
/**
	 * Determine if the supplied descriptor is for a supported number. The compilation
	 * process only (currently) supports certain number types. These are double, float,
	 * long and int.
	 * @param descriptor the descriptor for a type
	 * @return {@code true} if the descriptor is for a supported numeric type
	 */
	public static boolean isPrimitiveOrUnboxableSupportedNumber(@Nullable String descriptor) {
		if (descriptor == null) {
			return false;
		}
		if (descriptor.length() == 1) {
			return "DFIJ".contains(descriptor);
		}
		if (descriptor.startsWith("Ljava/lang/")) {
			String name = descriptor.substring("Ljava/lang/".length());
			if (name.equals("Double") || name.equals("Float") || name.equals("Integer") || name.equals("Long")) {
				return true;
			}
		}
		return false;
	}

	
Determine whether the given number is to be considered as an integer
for the purposes of a numeric operation at the bytecode level.

Params:
  • number – the number to check
Returns:true if it is an Integer, Short or Byte
/**
	 * Determine whether the given number is to be considered as an integer
	 * for the purposes of a numeric operation at the bytecode level.
	 * @param number the number to check
	 * @return {@code true} if it is an {@link Integer}, {@link Short} or {@link Byte}
	 */
	public static boolean isIntegerForNumericOp(Number number) {
		return (number instanceof Integer || number instanceof Short || number instanceof Byte);
	}

	
Convert a type descriptor to the single character primitive descriptor.

Params:
  • descriptor – a descriptor for a type that should have a primitive representation
Returns:the single character descriptor for a primitive input descriptor
/**
	 * Convert a type descriptor to the single character primitive descriptor.
	 * @param descriptor a descriptor for a type that should have a primitive representation
	 * @return the single character descriptor for a primitive input descriptor
	 */
	public static char toPrimitiveTargetDesc(String descriptor) {
		if (descriptor.length() == 1) {
			return descriptor.charAt(0);
		}
		else if (descriptor.equals("Ljava/lang/Boolean")) {
			return 'Z';
		}
		else if (descriptor.equals("Ljava/lang/Byte")) {
			return 'B';
		}
		else if (descriptor.equals("Ljava/lang/Character")) {
			return 'C';
		}
		else if (descriptor.equals("Ljava/lang/Double")) {
			return 'D';
		}
		else if (descriptor.equals("Ljava/lang/Float")) {
			return 'F';
		}
		else if (descriptor.equals("Ljava/lang/Integer")) {
			return 'I';
		}
		else if (descriptor.equals("Ljava/lang/Long")) {
			return 'J';
		}
		else if (descriptor.equals("Ljava/lang/Short")) {
			return 'S';
		}
		else {
			throw new IllegalStateException("No primitive for '" + descriptor + "'");
		}
	}

	
Insert the appropriate CHECKCAST instruction for the supplied descriptor.

Params:
  • mv – the target visitor into which the instruction should be inserted
  • descriptor – the descriptor of the type to cast to
/**
	 * Insert the appropriate CHECKCAST instruction for the supplied descriptor.
	 * @param mv the target visitor into which the instruction should be inserted
	 * @param descriptor the descriptor of the type to cast to
	 */
	public static void insertCheckCast(MethodVisitor mv, @Nullable String descriptor) {
		if (descriptor != null && descriptor.length() != 1) {
			if (descriptor.charAt(0) == '[') {
				if (isPrimitiveArray(descriptor)) {
					mv.visitTypeInsn(CHECKCAST, descriptor);
				}
				else {
					mv.visitTypeInsn(CHECKCAST, descriptor + ";");
				}
			}
			else {
				if (!descriptor.equals("Ljava/lang/Object")) {
					// This is chopping off the 'L' to leave us with "java/lang/String"
					mv.visitTypeInsn(CHECKCAST, descriptor.substring(1));
				}
			}
		}
	}

	
Determine the appropriate boxing instruction for a specific type (if it needs
boxing) and insert the instruction into the supplied visitor.

Params:
  • mv – the target visitor for the new instructions
  • descriptor – the descriptor of a type that may or may not need boxing
/**
	 * Determine the appropriate boxing instruction for a specific type (if it needs
	 * boxing) and insert the instruction into the supplied visitor.
	 * @param mv the target visitor for the new instructions
	 * @param descriptor the descriptor of a type that may or may not need boxing
	 */
	public static void insertBoxIfNecessary(MethodVisitor mv, @Nullable String descriptor) {
		if (descriptor != null && descriptor.length() == 1) {
			insertBoxIfNecessary(mv, descriptor.charAt(0));
		}
	}

	
Determine the appropriate boxing instruction for a specific type (if it needs
boxing) and insert the instruction into the supplied visitor.

Params:
  • mv – the target visitor for the new instructions
  • ch – the descriptor of the type that might need boxing
/**
	 * Determine the appropriate boxing instruction for a specific type (if it needs
	 * boxing) and insert the instruction into the supplied visitor.
	 * @param mv the target visitor for the new instructions
	 * @param ch the descriptor of the type that might need boxing
	 */
	public static void insertBoxIfNecessary(MethodVisitor mv, char ch) {
		switch (ch) {
			case 'Z':
				mv.visitMethodInsn(INVOKESTATIC, "java/lang/Boolean", "valueOf", "(Z)Ljava/lang/Boolean;", false);
				break;
			case 'B':
				mv.visitMethodInsn(INVOKESTATIC, "java/lang/Byte", "valueOf", "(B)Ljava/lang/Byte;", false);
				break;
			case 'C':
				mv.visitMethodInsn(INVOKESTATIC, "java/lang/Character", "valueOf", "(C)Ljava/lang/Character;", false);
				break;
			case 'D':
				mv.visitMethodInsn(INVOKESTATIC, "java/lang/Double", "valueOf", "(D)Ljava/lang/Double;", false);
				break;
			case 'F':
				mv.visitMethodInsn(INVOKESTATIC, "java/lang/Float", "valueOf", "(F)Ljava/lang/Float;", false);
				break;
			case 'I':
				mv.visitMethodInsn(INVOKESTATIC, "java/lang/Integer", "valueOf", "(I)Ljava/lang/Integer;", false);
				break;
			case 'J':
				mv.visitMethodInsn(INVOKESTATIC, "java/lang/Long", "valueOf", "(J)Ljava/lang/Long;", false);
				break;
			case 'S':
				mv.visitMethodInsn(INVOKESTATIC, "java/lang/Short", "valueOf", "(S)Ljava/lang/Short;", false);
				break;
			case 'L':
			case 'V':
			case '[':
				// no box needed
				break;
			default:
				throw new IllegalArgumentException("Boxing should not be attempted for descriptor '" + ch + "'");
		}
	}

	
Deduce the descriptor for a type. Descriptors are like JVM type names but missing the
trailing ';' so for Object the descriptor is "Ljava/lang/Object" for int it is "I".

Params:
  • type – the type (may be primitive) for which to determine the descriptor
Returns:the descriptor
/**
	 * Deduce the descriptor for a type. Descriptors are like JVM type names but missing the
	 * trailing ';' so for Object the descriptor is "Ljava/lang/Object" for int it is "I".
	 * @param type the type (may be primitive) for which to determine the descriptor
	 * @return the descriptor
	 */
	public static String toDescriptor(Class<?> type) {
		String name = type.getName();
		if (type.isPrimitive()) {
			switch (name.length()) {
				case 3:
					return "I";
				case 4:
					if (name.equals("byte")) {
						return "B";
					}
					else if (name.equals("char")) {
						return "C";
					}
					else if (name.equals("long")) {
						return "J";
					}
					else if (name.equals("void")) {
						return "V";
					}
					break;
				case 5:
					if (name.equals("float")) {
						return "F";
					}
					else if (name.equals("short")) {
						return "S";
					}
					break;
				case 6:
					if (name.equals("double")) {
						return "D";
					}
					break;
				case 7:
					if (name.equals("boolean")) {
						return "Z";
					}
					break;
			}
		}
		else {
			if (name.charAt(0) != '[') {
				return "L" + type.getName().replace('.', '/');
			}
			else {
				if (name.endsWith(";")) {
					return name.substring(0, name.length() - 1).replace('.', '/');
				}
				else {
					return name;  // array has primitive component type
				}
			}
		}
		return "";
	}

	
Create an array of descriptors representing the parameter types for the supplied
method. Returns a zero sized array if there are no parameters.

Params:
  • method – a Method
Returns:a String array of descriptors, one entry for each method parameter
/**
	 * Create an array of descriptors representing the parameter types for the supplied
	 * method. Returns a zero sized array if there are no parameters.
	 * @param method a Method
	 * @return a String array of descriptors, one entry for each method parameter
	 */
	public static String[] toParamDescriptors(Method method) {
		return toDescriptors(method.getParameterTypes());
	}

	
Create an array of descriptors representing the parameter types for the supplied
constructor. Returns a zero sized array if there are no parameters.

Params:
  • ctor – a Constructor
Returns:a String array of descriptors, one entry for each constructor parameter
/**
	 * Create an array of descriptors representing the parameter types for the supplied
	 * constructor. Returns a zero sized array if there are no parameters.
	 * @param ctor a Constructor
	 * @return a String array of descriptors, one entry for each constructor parameter
	 */
	public static String[] toParamDescriptors(Constructor<?> ctor) {
		return toDescriptors(ctor.getParameterTypes());
	}

	
Create an array of descriptors from an array of classes.

Params:
  • types – the input array of classes
Returns:an array of descriptors
/**
	 * Create an array of descriptors from an array of classes.
	 * @param types the input array of classes
	 * @return an array of descriptors
	 */
	public static String[] toDescriptors(Class<?>[] types) {
		int typesCount = types.length;
		String[] descriptors = new String[typesCount];
		for (int p = 0; p < typesCount; p++) {
			descriptors[p] = toDescriptor(types[p]);
		}
		return descriptors;
	}

	
Create the optimal instruction for loading a number on the stack.

Params:
  • mv – where to insert the bytecode
  • value – the value to be loaded
/**
	 * Create the optimal instruction for loading a number on the stack.
	 * @param mv where to insert the bytecode
	 * @param value the value to be loaded
	 */
	public static void insertOptimalLoad(MethodVisitor mv, int value) {
		if (value < 6) {
			mv.visitInsn(ICONST_0+value);
		}
		else if (value < Byte.MAX_VALUE) {
			mv.visitIntInsn(BIPUSH, value);
		}
		else if (value < Short.MAX_VALUE) {
			mv.visitIntInsn(SIPUSH, value);
		}
		else {
			mv.visitLdcInsn(value);
		}
	}

	
Produce appropriate bytecode to store a stack item in an array. The
instruction to use varies depending on whether the type
is a primitive or reference type.

Params:
  • mv – where to insert the bytecode
  • arrayElementType – the type of the array elements
/**
	 * Produce appropriate bytecode to store a stack item in an array. The
	 * instruction to use varies depending on whether the type
	 * is a primitive or reference type.
	 * @param mv where to insert the bytecode
	 * @param arrayElementType the type of the array elements
	 */
	public static void insertArrayStore(MethodVisitor mv, String arrayElementType) {
		if (arrayElementType.length()==1) {
			switch (arrayElementType.charAt(0)) {
				case 'I':
					mv.visitInsn(IASTORE);
					break;
				case 'J':
					mv.visitInsn(LASTORE);
					break;
				case 'F':
					mv.visitInsn(FASTORE);
					break;
				case 'D':
					mv.visitInsn(DASTORE);
					break;
				case 'B':
					mv.visitInsn(BASTORE);
					break;
				case 'C':
					mv.visitInsn(CASTORE);
					break;
				case 'S':
					mv.visitInsn(SASTORE);
					break;
				case 'Z':
					mv.visitInsn(BASTORE);
					break;
				default:
					throw new IllegalArgumentException(
							"Unexpected arraytype " + arrayElementType.charAt(0));
			}
		}
		else {
			mv.visitInsn(AASTORE);
		}
	}

	
Determine the appropriate T tag to use for the NEWARRAY bytecode.

Params:
  • arraytype – the array primitive component type
Returns:the T tag to use for NEWARRAY
/**
	 * Determine the appropriate T tag to use for the NEWARRAY bytecode.
	 * @param arraytype the array primitive component type
	 * @return the T tag to use for NEWARRAY
	 */
	public static int arrayCodeFor(String arraytype) {
		switch (arraytype.charAt(0)) {
			case 'I': return T_INT;
			case 'J': return T_LONG;
			case 'F': return T_FLOAT;
			case 'D': return T_DOUBLE;
			case 'B': return T_BYTE;
			case 'C': return T_CHAR;
			case 'S': return T_SHORT;
			case 'Z': return T_BOOLEAN;
			default:
				throw new IllegalArgumentException("Unexpected arraytype " + arraytype.charAt(0));
		}
	}

	
Return if the supplied array type has a core component reference type.

/**
	 * Return if the supplied array type has a core component reference type.
	 */
	public static boolean isReferenceTypeArray(String arraytype) {
		int length = arraytype.length();
		for (int i = 0; i < length; i++) {
			char ch = arraytype.charAt(i);
			if (ch == '[') {
				continue;
			}
			return (ch == 'L');
		}
		return false;
	}

	
Produce the correct bytecode to build an array. The opcode to use and the
signature to pass along with the opcode can vary depending on the signature
of the array type.

Params:
  • mv – the methodvisitor into which code should be inserted
  • size – the size of the array
  • arraytype – the type of the array
/**
	 * Produce the correct bytecode to build an array. The opcode to use and the
	 * signature to pass along with the opcode can vary depending on the signature
	 * of the array type.
	 * @param mv the methodvisitor into which code should be inserted
	 * @param size the size of the array
	 * @param arraytype the type of the array
	 */
	public static void insertNewArrayCode(MethodVisitor mv, int size, String arraytype) {
		insertOptimalLoad(mv, size);
		if (arraytype.length() == 1) {
			mv.visitIntInsn(NEWARRAY, CodeFlow.arrayCodeFor(arraytype));
		}
		else {
			if (arraytype.charAt(0) == '[') {
				// Handling the nested array case here.
				// If vararg is [[I then we want [I and not [I;
				if (CodeFlow.isReferenceTypeArray(arraytype)) {
					mv.visitTypeInsn(ANEWARRAY, arraytype + ";");
				}
				else {
					mv.visitTypeInsn(ANEWARRAY, arraytype);
				}
			}
			else {
				mv.visitTypeInsn(ANEWARRAY, arraytype.substring(1));
			}
		}
	}

	
For use in mathematical operators, handles converting from a (possibly boxed)
number on the stack to a primitive numeric type.

For example, from a Integer to a double, just need to call 'Number.doubleValue()'
but from an int to a double, need to use the bytecode 'i2d'.

Params:
  • mv – the method visitor when instructions should be appended
  • stackDescriptor – a descriptor of the operand on the stack
  • targetDescriptor – a primitive type descriptor
/**
	 * For use in mathematical operators, handles converting from a (possibly boxed)
	 * number on the stack to a primitive numeric type.
	 * <p>For example, from a Integer to a double, just need to call 'Number.doubleValue()'
	 * but from an int to a double, need to use the bytecode 'i2d'.
	 * @param mv the method visitor when instructions should be appended
	 * @param stackDescriptor a descriptor of the operand on the stack
	 * @param targetDescriptor a primitive type descriptor
	 */
	public static void insertNumericUnboxOrPrimitiveTypeCoercion(
			MethodVisitor mv, @Nullable String stackDescriptor, char targetDescriptor) {

		if (!CodeFlow.isPrimitive(stackDescriptor)) {
			CodeFlow.insertUnboxNumberInsns(mv, targetDescriptor, stackDescriptor);
		}
		else {
			CodeFlow.insertAnyNecessaryTypeConversionBytecodes(mv, targetDescriptor, stackDescriptor);
		}
	}

	public static String toBoxedDescriptor(String primitiveDescriptor) {
		switch (primitiveDescriptor.charAt(0)) {
			case 'I': return "Ljava/lang/Integer";
			case 'J': return "Ljava/lang/Long";
			case 'F': return "Ljava/lang/Float";
			case 'D': return "Ljava/lang/Double";
			case 'B': return "Ljava/lang/Byte";
			case 'C': return "Ljava/lang/Character";
			case 'S': return "Ljava/lang/Short";
			case 'Z': return "Ljava/lang/Boolean";
			default:
				throw new IllegalArgumentException("Unexpected non primitive descriptor " + primitiveDescriptor);
		}
	}


	
Interface used to generate fields.

/**
	 * Interface used to generate fields.
	 */
	@FunctionalInterface
	public interface FieldAdder {

		void generateField(ClassWriter cw, CodeFlow codeflow);
	}


	
Interface used to generate clinit static initializer blocks. 
/**
	 * Interface used to generate {@code clinit} static initializer blocks.
	 */
	@FunctionalInterface
	public interface ClinitAdder {

		void generateCode(MethodVisitor mv, CodeFlow codeflow);
	}

}