stringconcatenation.java

一个查找java程序里bug的程序的源代码,该程序本身也是java写的,对提高java编程水平很有用

/*
 * FindBugs - Find bugs in Java programs
 * Copyright (C) 2004 Dave Brosius <[e-mail]>
 * Copyright (C) 2004 University of Maryland
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.detect;

import edu.umd.cs.findbugs.BugInstance;
import edu.umd.cs.findbugs.BugReporter;
import edu.umd.cs.findbugs.BytecodeScanningDetector;
import edu.umd.cs.findbugs.visitclass.Constants2;
import org.apache.bcel.classfile.Method;

/**
 * Find occurrences of using the String "+" or "+=" operators
 * within a loop.  This is much less efficient than creating
 * a dedicated StringBuffer object outside the loop, and
 * then appending to it.
 *
 * @author Dave Brosius
 * @author William Pugh
 */
public class StringConcatenation extends BytecodeScanningDetector implements Constants2 {
	private static final boolean DEBUG
	        = Boolean.getBoolean("sbsc.debug");

	static final int SEEN_NOTHING = 0;
	static final int SEEN_NEW = 1;
	static final int SEEN_APPEND1 = 2;
	static final int SEEN_APPEND2 = 3;
	static final int CONSTRUCTED_STRING_ON_STACK = 4;
	static final int POSSIBLE_CASE = 5;

	private BugReporter bugReporter;
	private boolean reportedThisMethod;

	private int registerOnStack = -1;
	private int stringSource = -1;
	private int createPC = -1;
	private int state = SEEN_NOTHING;

	public StringConcatenation(BugReporter bugReporter) {
		this.bugReporter = bugReporter;
	}

	public void visit(Method obj) {
		if (DEBUG)
			System.out.println("------------------- Analyzing " + obj.getName() + " ----------------");
		reset();
		reportedThisMethod = false;
		super.visit(obj);
	}

	private void reset() {
		state = SEEN_NOTHING;
		createPC = -1;
		registerOnStack = -1;
		stringSource = -1;

		// For debugging: print what call to reset() is being invoked.
		// This helps figure out why the detector is failing to
		// recognize a particular idiom.
		if (DEBUG) System.out.println("Reset from: " + new Throwable().getStackTrace()[1]);
	}

	private boolean storeIntoRegister(int seen, int reg) {
		switch (seen) {
		case ASTORE_0:
			return reg == 0;
		case ASTORE_1:
			return reg == 1;
		case ASTORE_2:
			return reg == 2;
		case ASTORE_3:
			return reg == 3;
		case ASTORE:
			return reg == getRegisterOperand();
		default:
			return false;
		}
	}

	public void sawOpcode(int seen) {
		if (reportedThisMethod) return;
		int oldState = state;
		if (DEBUG) System.out.println("Opcode: " + OPCODE_NAMES[seen]);
		switch (state) {
		case SEEN_NOTHING:
			if ((seen == NEW)
			        &&
			        getClassConstantOperand().startsWith("java/lang/StringBu")) {
				state = SEEN_NEW;
				createPC = getPC();
			}
			break;

		case SEEN_NEW:
			if (DEBUG && seen == INVOKEVIRTUAL) {
				System.out.println("Invoke virtual");
				System.out.println("   " + getNameConstantOperand());
				System.out.println("   " + getClassConstantOperand());
				System.out.println("   " + getSigConstantOperand());
			}
			if (seen == INVOKEVIRTUAL
			        && "append".equals(getNameConstantOperand())
			        && getClassConstantOperand().startsWith("java/lang/StringBu")) {
				if (DEBUG) System.out.println("Saw string being appended from register " + registerOnStack);
				if (getSigConstantOperand().startsWith("(Ljava/lang/String;)")
				        && registerOnStack >= 0) {
					if (DEBUG)
						System.out.println("Saw string being appended, source = " + registerOnStack);
					state = SEEN_APPEND1;
					stringSource = registerOnStack;
				} else
					reset();
			}
			break;
		case SEEN_APPEND1:
			if (storeIntoRegister(seen, stringSource))
				reset();
			else if (seen == INVOKEVIRTUAL
			        && "append".equals(getNameConstantOperand())
			        && getClassConstantOperand().startsWith("java/lang/StringBu")) {
				state = SEEN_APPEND2;
			}
			break;

		case SEEN_APPEND2:
			if (storeIntoRegister(seen, stringSource))
				reset();
			else if (seen == INVOKEVIRTUAL
			        && "toString".equals(getNameConstantOperand())
			        && getClassConstantOperand().startsWith("java/lang/StringBu")) {
				state = CONSTRUCTED_STRING_ON_STACK;
			}
			break;

		case CONSTRUCTED_STRING_ON_STACK:
			if (storeIntoRegister(seen, stringSource))
				state = POSSIBLE_CASE;
			else
				reset();
			break;

		case POSSIBLE_CASE:
			if (seen == GOTO
			        && (getPC() - getBranchTarget()) < 300
			        && getBranchTarget() < createPC) {
				bugReporter.reportBug(new BugInstance(this, "SBSC_USE_STRINGBUFFER_CONCATENATION", NORMAL_PRIORITY)
				        .addClassAndMethod(this)
				        .addSourceLine(this, createPC));
				// System.out.println("SBSC spread: " + (getPC() - getBranchTarget()));
				reset();
				reportedThisMethod = true;
			} else if ((seen == NEW)
			        &&
			        getClassConstantOperand().startsWith("java/lang/StringBu")) {
				state = SEEN_NEW;
				createPC = getPC();
			}
			break;
		}
		registerOnStack = -1;
		switch (seen) {
		case ALOAD_0:
			registerOnStack = 0;
			break;
		case ALOAD_1:
			registerOnStack = 1;
			break;
		case ALOAD_2:
			registerOnStack = 2;
			break;
		case ALOAD_3:
			registerOnStack = 3;
			break;
		case ALOAD:
			registerOnStack = getRegisterOperand();
			break;
		}
		if (DEBUG && state != oldState)
			System.out.println("At PC " + getPC()
			        + " changing from state " + oldState
			        + " to state " + state
			        + ", regOnStack = " + registerOnStack);
	}
}

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