plastic/src/external/java/org/apache/tapestry5/internal/plastic/asm/commons/TryCatchBlockSorter.java

// ASM: a very small and fast Java bytecode manipulation framework
// Copyright (c) 2000-2011 INRIA, France Telecom
// All rights reserved.
//
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// modification, are permitted provided that the following conditions
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// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
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//    contributors may be used to endorse or promote products derived from
//    this software without specific prior written permission.
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package org.apache.tapestry5.internal.plastic.asm.commons;

import java.util.Collections;
import java.util.Comparator;
import org.apache.tapestry5.internal.plastic.asm.MethodVisitor;
import org.apache.tapestry5.internal.plastic.asm.Opcodes;
import org.apache.tapestry5.internal.plastic.asm.tree.MethodNode;
import org.apache.tapestry5.internal.plastic.asm.tree.TryCatchBlockNode;

/**
 * A {@link MethodVisitor} adapter to sort the exception handlers. The handlers are sorted in a
 * method innermost-to-outermost. This allows the programmer to add handlers without worrying about
 * ordering them correctly with respect to existing, in-code handlers.
 *
 * <p>Behavior is only defined for properly-nested handlers. If any "try" blocks overlap (something
 * that isn't possible in Java code) then this may not do what you want. In fact, this adapter just
 * sorts by the length of the "try" block, taking advantage of the fact that a given try block must
 * be larger than any block it contains).
 *
 * @author Adrian Sampson
 */
public class TryCatchBlockSorter extends MethodNode {

  /**
   * Constructs a new {@link TryCatchBlockSorter}.
   *
   * @param methodVisitor the method visitor to which this visitor must delegate method calls. May
   *     be {@literal null}.
   * @param access the method's access flags (see {@link Opcodes}). This parameter also indicates if
   *     the method is synthetic and/or deprecated.
   * @param name the method's name.
   * @param descriptor the method's descriptor (see {@link org.apache.tapestry5.internal.plastic.asm.Type}).
   * @param signature the method's signature. May be {@literal null} if the method parameters,
   *     return type and exceptions do not use generic types.
   * @param exceptions the internal names of the method's exception classes (see {@link
   *     org.apache.tapestry5.internal.plastic.asm.Type#getInternalName()}). May be {@literal null}.
   */
  public TryCatchBlockSorter(
      final MethodVisitor methodVisitor,
      final int access,
      final String name,
      final String descriptor,
      final String signature,
      final String[] exceptions) {
    this(
        /* latest api = */ Opcodes.ASM8,
        methodVisitor,
        access,
        name,
        descriptor,
        signature,
        exceptions);
    if (getClass() != TryCatchBlockSorter.class) {
      throw new IllegalStateException();
    }
  }

  protected TryCatchBlockSorter(
      final int api,
      final MethodVisitor methodVisitor,
      final int access,
      final String name,
      final String descriptor,
      final String signature,
      final String[] exceptions) {
    super(api, access, name, descriptor, signature, exceptions);
    this.mv = methodVisitor;
  }

  @Override
  public void visitEnd() {
    // Sort the TryCatchBlockNode elements by the length of their "try" block.
    Collections.sort(
        tryCatchBlocks,
        new Comparator<TryCatchBlockNode>() {

          @Override
          public int compare(
              final TryCatchBlockNode tryCatchBlockNode1,
              final TryCatchBlockNode tryCatchBlockNode2) {
            return blockLength(tryCatchBlockNode1) - blockLength(tryCatchBlockNode2);
          }

          private int blockLength(final TryCatchBlockNode tryCatchBlockNode) {
            int startIndex = instructions.indexOf(tryCatchBlockNode.start);
            int endIndex = instructions.indexOf(tryCatchBlockNode.end);
            return endIndex - startIndex;
          }
        });
    // Update the 'target' of each try catch block annotation.
    for (int i = 0; i < tryCatchBlocks.size(); ++i) {
      tryCatchBlocks.get(i).updateIndex(i);
    }
    if (mv != null) {
      accept(mv);
    }
  }
}