commons-bcel-master/src/main/java/org/apache/bcel/verifier/PassVerifier.java
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.bcel.verifier;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.lang3.ArrayUtils;

/**
 * A PassVerifier actually verifies a class file; it is instantiated by a Verifier. The verification should conform with
 * a certain pass as described in The Java Virtual Machine Specification, 2nd edition. This book describes four passes.
 * Pass one means loading the class and verifying a few static constraints. Pass two actually verifies some other
 * constraints that could enforce loading in referenced class files. Pass three is the first pass that actually checks
 * constraints in the code array of a method in the class file; it has two parts with the first verifying static
 * constraints and the second part verifying structural constraints (where a data flow analysis is used for). The fourth
 * pass, finally, performs checks that can only be done at run-time. JustIce does not have a run-time pass, but certain
 * constraints that are usually delayed until run-time for performance reasons are also checked during the second part
 * of pass three. PassVerifier instances perform caching. That means, if you really want a new verification run of a
 * certain pass you must use a new instance of a given PassVerifier.
 *
 * @see Verifier
 * @see #verify()
 */
public abstract class PassVerifier {

    /** The (warning) messages. */
    private final List<String> messages = new ArrayList<>();
    /** The VerificationResult cache. */
    private VerificationResult verificationResult;

    /**
     * This method adds a (warning) message to the message pool of this PassVerifier. This method is normally only
     * internally used by BCEL's class file verifier "JustIce" and should not be used from the outside.
     *
     * @param message message to be appended to the message list.
     * @see #getMessages()
     */
    public void addMessage(final String message) {
        messages.add(message);
    }

    /**
     * Verifies, not cached.
     *
     * @return The VerificationResult
     */
    public abstract VerificationResult do_verify();

    /**
     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
     *
     * @return the (warning) messages.
     * @see #addMessage(String)
     * @see #do_verify()
     */
    public String[] getMessages() {
        return getMessagesList().toArray(ArrayUtils.EMPTY_STRING_ARRAY);
    }

    /**
     * Returns the (warning) messages that this PassVerifier accumulated during its do_verify()ing work.
     *
     * @see #addMessage(String)
     * @see #do_verify()
     */
    public List<String> getMessagesList() {
        verify(); // create messages if not already done (cached!)
        return messages;
    }

    /**
     * This method runs a verification pass conforming to the Java Virtual Machine Specification, 2nd edition, on a class
     * file. PassVerifier instances perform caching; i.e. if the verify() method once determined a VerificationResult, then
     * this result may be returned after every invocation of this method instead of running the verification pass anew;
     * likewise with the result of getMessages().
     *
     * @return a VerificationResult.
     * @see #getMessages()
     * @see #addMessage(String)
     */
    public VerificationResult verify() {
        if (verificationResult == null) {
            verificationResult = do_verify();
        }
        return verificationResult;
    }
}
