org.mvel2.asm.signature.SignatureWriter Maven / Gradle / Ivy
// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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//
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// 2. Redistributions in binary form must reproduce the above copyright
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//
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package org.mvel2.asm.signature;
import org.mvel2.asm.Opcodes;
/**
* A SignatureVisitor that generates signature literals, as defined in the Java Virtual Machine
* Specification (JVMS).
*
* @see JVMS
* 4.7.9.1
* @author Thomas Hallgren
* @author Eric Bruneton
*/
public class SignatureWriter extends SignatureVisitor {
/** The builder used to construct the visited signature. */
private final StringBuilder stringBuilder = new StringBuilder();
/** Whether the visited signature contains formal type parameters. */
private boolean hasFormals;
/** Whether the visited signature contains method parameter types. */
private boolean hasParameters;
/**
* The stack used to keep track of class types that have arguments. Each element of this stack is
* a boolean encoded in one bit. The top of the stack is the least significant bit. Pushing false
* = *2, pushing true = *2+1, popping = /2.
*
* Class type arguments must be surrounded with '<' and '>' and, because
*
*
* - class types can be nested (because type arguments can themselves be class types),
*
- SignatureWriter always returns 'this' in each visit* method (to avoid allocating new
* SignatureWriter instances),
*
*
* we need a stack to properly balance these 'parentheses'. A new element is pushed on this
* stack for each new visited type, and popped when the visit of this type ends (either is
* visitEnd, or because visitInnerClassType is called).
*/
private int argumentStack;
/** Constructs a new {@link SignatureWriter}. */
public SignatureWriter() {
super(Opcodes.ASM7);
}
// -----------------------------------------------------------------------------------------------
// Implementation of the SignatureVisitor interface
// -----------------------------------------------------------------------------------------------
@Override
public void visitFormalTypeParameter(final String name) {
if (!hasFormals) {
hasFormals = true;
stringBuilder.append('<');
}
stringBuilder.append(name);
stringBuilder.append(':');
}
@Override
public SignatureVisitor visitClassBound() {
return this;
}
@Override
public SignatureVisitor visitInterfaceBound() {
stringBuilder.append(':');
return this;
}
@Override
public SignatureVisitor visitSuperclass() {
endFormals();
return this;
}
@Override
public SignatureVisitor visitInterface() {
return this;
}
@Override
public SignatureVisitor visitParameterType() {
endFormals();
if (!hasParameters) {
hasParameters = true;
stringBuilder.append('(');
}
return this;
}
@Override
public SignatureVisitor visitReturnType() {
endFormals();
if (!hasParameters) {
stringBuilder.append('(');
}
stringBuilder.append(')');
return this;
}
@Override
public SignatureVisitor visitExceptionType() {
stringBuilder.append('^');
return this;
}
@Override
public void visitBaseType(final char descriptor) {
stringBuilder.append(descriptor);
}
@Override
public void visitTypeVariable(final String name) {
stringBuilder.append('T');
stringBuilder.append(name);
stringBuilder.append(';');
}
@Override
public SignatureVisitor visitArrayType() {
stringBuilder.append('[');
return this;
}
@Override
public void visitClassType(final String name) {
stringBuilder.append('L');
stringBuilder.append(name);
// Pushes 'false' on the stack, meaning that this type does not have type arguments (as far as
// we can tell at this point).
argumentStack *= 2;
}
@Override
public void visitInnerClassType(final String name) {
endArguments();
stringBuilder.append('.');
stringBuilder.append(name);
// Pushes 'false' on the stack, meaning that this type does not have type arguments (as far as
// we can tell at this point).
argumentStack *= 2;
}
@Override
public void visitTypeArgument() {
// If the top of the stack is 'false', this means we are visiting the first type argument of the
// currently visited type. We therefore need to append a '<', and to replace the top stack
// element with 'true' (meaning that the current type does have type arguments).
if (argumentStack % 2 == 0) {
argumentStack |= 1;
stringBuilder.append('<');
}
stringBuilder.append('*');
}
@Override
public SignatureVisitor visitTypeArgument(final char wildcard) {
// If the top of the stack is 'false', this means we are visiting the first type argument of the
// currently visited type. We therefore need to append a '<', and to replace the top stack
// element with 'true' (meaning that the current type does have type arguments).
if (argumentStack % 2 == 0) {
argumentStack |= 1;
stringBuilder.append('<');
}
if (wildcard != '=') {
stringBuilder.append(wildcard);
}
return this;
}
@Override
public void visitEnd() {
endArguments();
stringBuilder.append(';');
}
/**
* Returns the signature that was built by this signature writer.
*
* @return the signature that was built by this signature writer.
*/
@Override
public String toString() {
return stringBuilder.toString();
}
// -----------------------------------------------------------------------------------------------
// Utility methods
// -----------------------------------------------------------------------------------------------
/** Ends the formal type parameters section of the signature. */
private void endFormals() {
if (hasFormals) {
hasFormals = false;
stringBuilder.append('>');
}
}
/** Ends the type arguments of a class or inner class type. */
private void endArguments() {
// If the top of the stack is 'true', this means that some type arguments have been visited for
// the type whose visit is now ending. We therefore need to append a '>', and to pop one element
// from the stack.
if (argumentStack % 2 == 1) {
stringBuilder.append('>');
}
argumentStack /= 2;
}
}