http://asm.ow2.io/: Usefull class adapters based on ASM, a very small and fast Java bytecode manipulation framework (OW2)
  • Eric Bruneton
  • Eugene Kuleshov
  • Remi Forax 
// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
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package org.objectweb.asm.commons;

import org.objectweb.asm.AnnotationVisitor;
import org.objectweb.asm.Label;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
import org.objectweb.asm.Type;
import org.objectweb.asm.TypePath;


A MethodVisitor that renumbers local variables in their order of appearance. This adapter allows one to easily add new local variables to a method. It may be used by inheriting from this class, but the preferred way of using it is via delegation: the next visitor in the chain can indeed add new locals when needed by calling newLocal on this adapter (this requires a reference back to this LocalVariablesSorter). 
Author:Chris Nokleberg, Eugene Kuleshov, Eric Bruneton
/**
 * A {@link MethodVisitor} that renumbers local variables in their order of appearance. This adapter
 * allows one to easily add new local variables to a method. It may be used by inheriting from this
 * class, but the preferred way of using it is via delegation: the next visitor in the chain can
 * indeed add new locals when needed by calling {@link #newLocal} on this adapter (this requires a
 * reference back to this {@link LocalVariablesSorter}).
 *
 * @author Chris Nokleberg
 * @author Eugene Kuleshov
 * @author Eric Bruneton
 */
public class LocalVariablesSorter extends MethodVisitor {

  
The type of the java.lang.Object class. 
/** The type of the java.lang.Object class. */
  private static final Type OBJECT_TYPE = Type.getObjectType("java/lang/Object");

  
The mapping from old to new local variable indices. A local variable at index i of size 1 is
remapped to 'mapping[2*i]', while a local variable at index i of size 2 is remapped to
'mapping[2*i+1]'.

/**
   * The mapping from old to new local variable indices. A local variable at index i of size 1 is
   * remapped to 'mapping[2*i]', while a local variable at index i of size 2 is remapped to
   * 'mapping[2*i+1]'.
   */
  private int[] remappedVariableIndices = new int[40];

  
The local variable types after remapping. The format of this array is the same as in MethodVisitor.visitFrame, except that long and double types use two slots. 
/**
   * The local variable types after remapping. The format of this array is the same as in {@link
   * MethodVisitor#visitFrame}, except that long and double types use two slots.
   */
  private Object[] remappedLocalTypes = new Object[20];

  
The index of the first local variable, after formal parameters. 
/** The index of the first local variable, after formal parameters. */
  protected final int firstLocal;

  
The index of the next local variable to be created by newLocal. 
/** The index of the next local variable to be created by {@link #newLocal}. */
  protected int nextLocal;

  
Constructs a new LocalVariablesSorter. Subclasses must not use this constructor. Instead, they must use the LocalVariablesSorter(int, int, String, MethodVisitor) version. 
Params:
  • access – access flags of the adapted method.
  • descriptor – the method's descriptor (see Type).
  • methodVisitor – the method visitor to which this adapter delegates calls.
Throws:
/**
   * Constructs a new {@link LocalVariablesSorter}. <i>Subclasses must not use this constructor</i>.
   * Instead, they must use the {@link #LocalVariablesSorter(int, int, String, MethodVisitor)}
   * version.
   *
   * @param access access flags of the adapted method.
   * @param descriptor the method's descriptor (see {@link Type}).
   * @param methodVisitor the method visitor to which this adapter delegates calls.
   * @throws IllegalStateException if a subclass calls this constructor.
   */
  public LocalVariablesSorter(
      final int access, final String descriptor, final MethodVisitor methodVisitor) {
    this(/* latest api = */ Opcodes.ASM9, access, descriptor, methodVisitor);
    if (getClass() != LocalVariablesSorter.class) {
      throw new IllegalStateException();
    }
  }

  
Constructs a new LocalVariablesSorter. 
Params:
/**
   * Constructs a new {@link LocalVariablesSorter}.
   *
   * @param api the ASM API version implemented by this visitor. Must be one of {@link
   *     Opcodes#ASM4}, {@link Opcodes#ASM5}, {@link Opcodes#ASM6}, {@link Opcodes#ASM7}, {@link
   *     Opcodes#ASM8} or {@link Opcodes#ASM9}.
   * @param access access flags of the adapted method.
   * @param descriptor the method's descriptor (see {@link Type}).
   * @param methodVisitor the method visitor to which this adapter delegates calls.
   */
  protected LocalVariablesSorter(
      final int api, final int access, final String descriptor, final MethodVisitor methodVisitor) {
    super(api, methodVisitor);
    nextLocal = (Opcodes.ACC_STATIC & access) == 0 ? 1 : 0;
    for (Type argumentType : Type.getArgumentTypes(descriptor)) {
      nextLocal += argumentType.getSize();
    }
    firstLocal = nextLocal;
  }

  @Override
  public void visitVarInsn(final int opcode, final int var) {
    Type varType;
    switch (opcode) {
      case Opcodes.LLOAD:
      case Opcodes.LSTORE:
        varType = Type.LONG_TYPE;
        break;
      case Opcodes.DLOAD:
      case Opcodes.DSTORE:
        varType = Type.DOUBLE_TYPE;
        break;
      case Opcodes.FLOAD:
      case Opcodes.FSTORE:
        varType = Type.FLOAT_TYPE;
        break;
      case Opcodes.ILOAD:
      case Opcodes.ISTORE:
        varType = Type.INT_TYPE;
        break;
      case Opcodes.ALOAD:
      case Opcodes.ASTORE:
      case Opcodes.RET:
        varType = OBJECT_TYPE;
        break;
      default:
        throw new IllegalArgumentException("Invalid opcode " + opcode);
    }
    super.visitVarInsn(opcode, remap(var, varType));
  }

  @Override
  public void visitIincInsn(final int var, final int increment) {
    super.visitIincInsn(remap(var, Type.INT_TYPE), increment);
  }

  @Override
  public void visitMaxs(final int maxStack, final int maxLocals) {
    super.visitMaxs(maxStack, nextLocal);
  }

  @Override
  public void visitLocalVariable(
      final String name,
      final String descriptor,
      final String signature,
      final Label start,
      final Label end,
      final int index) {
    int remappedIndex = remap(index, Type.getType(descriptor));
    super.visitLocalVariable(name, descriptor, signature, start, end, remappedIndex);
  }

  @Override
  public AnnotationVisitor visitLocalVariableAnnotation(
      final int typeRef,
      final TypePath typePath,
      final Label[] start,
      final Label[] end,
      final int[] index,
      final String descriptor,
      final boolean visible) {
    Type type = Type.getType(descriptor);
    int[] remappedIndex = new int[index.length];
    for (int i = 0; i < remappedIndex.length; ++i) {
      remappedIndex[i] = remap(index[i], type);
    }
    return super.visitLocalVariableAnnotation(
        typeRef, typePath, start, end, remappedIndex, descriptor, visible);
  }

  @Override
  public void visitFrame(
      final int type,
      final int numLocal,
      final Object[] local,
      final int numStack,
      final Object[] stack) {
    if (type != Opcodes.F_NEW) { // Uncompressed frame.
      throw new IllegalArgumentException(
          "LocalVariablesSorter only accepts expanded frames (see ClassReader.EXPAND_FRAMES)");
    }

    // Create a copy of remappedLocals.
    Object[] oldRemappedLocals = new Object[remappedLocalTypes.length];
    System.arraycopy(remappedLocalTypes, 0, oldRemappedLocals, 0, oldRemappedLocals.length);

    updateNewLocals(remappedLocalTypes);

    // Copy the types from 'local' to 'remappedLocals'. 'remappedLocals' already contains the
    // variables added with 'newLocal'.
    int oldVar = 0; // Old local variable index.
    for (int i = 0; i < numLocal; ++i) {
      Object localType = local[i];
      if (localType != Opcodes.TOP) {
        Type varType = OBJECT_TYPE;
        if (localType == Opcodes.INTEGER) {
          varType = Type.INT_TYPE;
        } else if (localType == Opcodes.FLOAT) {
          varType = Type.FLOAT_TYPE;
        } else if (localType == Opcodes.LONG) {
          varType = Type.LONG_TYPE;
        } else if (localType == Opcodes.DOUBLE) {
          varType = Type.DOUBLE_TYPE;
        } else if (localType instanceof String) {
          varType = Type.getObjectType((String) localType);
        }
        setFrameLocal(remap(oldVar, varType), localType);
      }
      oldVar += localType == Opcodes.LONG || localType == Opcodes.DOUBLE ? 2 : 1;
    }

    // Remove TOP after long and double types as well as trailing TOPs.
    oldVar = 0;
    int newVar = 0;
    int remappedNumLocal = 0;
    while (oldVar < remappedLocalTypes.length) {
      Object localType = remappedLocalTypes[oldVar];
      oldVar += localType == Opcodes.LONG || localType == Opcodes.DOUBLE ? 2 : 1;
      if (localType != null && localType != Opcodes.TOP) {
        remappedLocalTypes[newVar++] = localType;
        remappedNumLocal = newVar;
      } else {
        remappedLocalTypes[newVar++] = Opcodes.TOP;
      }
    }

    // Visit the remapped frame.
    super.visitFrame(type, remappedNumLocal, remappedLocalTypes, numStack, stack);

    // Restore the original value of 'remappedLocals'.
    remappedLocalTypes = oldRemappedLocals;
  }

  // -----------------------------------------------------------------------------------------------

  
Constructs a new local variable of the given type.

Params:
  • type – the type of the local variable to be created.
Returns:the identifier of the newly created local variable.
/**
   * Constructs a new local variable of the given type.
   *
   * @param type the type of the local variable to be created.
   * @return the identifier of the newly created local variable.
   */
  public int newLocal(final Type type) {
    Object localType;
    switch (type.getSort()) {
      case Type.BOOLEAN:
      case Type.CHAR:
      case Type.BYTE:
      case Type.SHORT:
      case Type.INT:
        localType = Opcodes.INTEGER;
        break;
      case Type.FLOAT:
        localType = Opcodes.FLOAT;
        break;
      case Type.LONG:
        localType = Opcodes.LONG;
        break;
      case Type.DOUBLE:
        localType = Opcodes.DOUBLE;
        break;
      case Type.ARRAY:
        localType = type.getDescriptor();
        break;
      case Type.OBJECT:
        localType = type.getInternalName();
        break;
      default:
        throw new AssertionError();
    }
    int local = newLocalMapping(type);
    setLocalType(local, type);
    setFrameLocal(local, localType);
    return local;
  }

  
Notifies subclasses that a new stack map frame is being visited. The array argument contains the stack map frame types corresponding to the local variables added with newLocal. This method can update these types in place for the stack map frame being visited. The default implementation of this method does nothing, i.e. a local variable added with newLocal will have the same type in all stack map frames. But this behavior is not always the desired one, for instance if a local variable is added in the middle of a try/catch block: the frame for the exception handler should have a TOP type for this new local. 
Params:
  • newLocals – the stack map frame types corresponding to the local variables added with newLocal (and null for the others). The format of this array is the same as in MethodVisitor.visitFrame, except that long and double types use two slots. The types for the current stack map frame must be updated in place in this array.
/**
   * Notifies subclasses that a new stack map frame is being visited. The array argument contains
   * the stack map frame types corresponding to the local variables added with {@link #newLocal}.
   * This method can update these types in place for the stack map frame being visited. The default
   * implementation of this method does nothing, i.e. a local variable added with {@link #newLocal}
   * will have the same type in all stack map frames. But this behavior is not always the desired
   * one, for instance if a local variable is added in the middle of a try/catch block: the frame
   * for the exception handler should have a TOP type for this new local.
   *
   * @param newLocals the stack map frame types corresponding to the local variables added with
   *     {@link #newLocal} (and null for the others). The format of this array is the same as in
   *     {@link MethodVisitor#visitFrame}, except that long and double types use two slots. The
   *     types for the current stack map frame must be updated in place in this array.
   */
  protected void updateNewLocals(final Object[] newLocals) {
    // The default implementation does nothing.
  }

  
Notifies subclasses that a local variable has been added or remapped. The default
implementation of this method does nothing.

Params:
  • local – a local variable identifier, as returned by newLocal.
  • type – the type of the value being stored in the local variable.
/**
   * Notifies subclasses that a local variable has been added or remapped. The default
   * implementation of this method does nothing.
   *
   * @param local a local variable identifier, as returned by {@link #newLocal}.
   * @param type the type of the value being stored in the local variable.
   */
  protected void setLocalType(final int local, final Type type) {
    // The default implementation does nothing.
  }

  private void setFrameLocal(final int local, final Object type) {
    int numLocals = remappedLocalTypes.length;
    if (local >= numLocals) {
      Object[] newRemappedLocalTypes = new Object[Math.max(2 * numLocals, local + 1)];
      System.arraycopy(remappedLocalTypes, 0, newRemappedLocalTypes, 0, numLocals);
      remappedLocalTypes = newRemappedLocalTypes;
    }
    remappedLocalTypes[local] = type;
  }

  private int remap(final int var, final Type type) {
    if (var + type.getSize() <= firstLocal) {
      return var;
    }
    int key = 2 * var + type.getSize() - 1;
    int size = remappedVariableIndices.length;
    if (key >= size) {
      int[] newRemappedVariableIndices = new int[Math.max(2 * size, key + 1)];
      System.arraycopy(remappedVariableIndices, 0, newRemappedVariableIndices, 0, size);
      remappedVariableIndices = newRemappedVariableIndices;
    }
    int value = remappedVariableIndices[key];
    if (value == 0) {
      value = newLocalMapping(type);
      setLocalType(value, type);
      remappedVariableIndices[key] = value + 1;
    } else {
      value--;
    }
    return value;
  }

  protected int newLocalMapping(final Type type) {
    int local = nextLocal;
    nextLocal += type.getSize();
    return local;
  }
}