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1
20
21 package edu.umd.cs.findbugs.detect;
22
23
24 import edu.umd.cs.findbugs.*;
25
26 import org.apache.bcel.classfile.Method;
27
28
37 public class StringConcatenation extends BytecodeScanningDetector implements StatelessDetector {
38 private static final boolean DEBUG
39 = SystemProperties.getBoolean("sbsc.debug");
40
41 static final int SEEN_NOTHING = 0;
42 static final int SEEN_NEW = 1;
43 static final int SEEN_APPEND1 = 2;
44 static final int SEEN_APPEND2 = 3;
45 static final int CONSTRUCTED_STRING_ON_STACK = 4;
46 static final int POSSIBLE_CASE = 5;
47
48 private BugReporter bugReporter;
49 private boolean reportedThisMethod;
50
51 private int registerOnStack = -1;
52 private int stringSource = -1;
53 private int createPC = -1;
54 private int state = SEEN_NOTHING;
55
56 public StringConcatenation(BugReporter bugReporter) {
57 this.bugReporter = bugReporter;
58 }
59
60
61
62 @Override 
63 public void visit(Method obj) {
64 if (DEBUG)
65 System.out.println("------------------- Analyzing " + obj.getName() + " ----------------");
66 reset();
67 reportedThisMethod = false;
68 super.visit(obj);
69 }
70
71 private void reset() {
72 state = SEEN_NOTHING;
73 createPC = -1;
74 registerOnStack = -1;
75 stringSource = -1;
76
77 if (DEBUG) System.out.println("Reset from: " + new Throwable ().getStackTrace()[1]);
81 }
82
83 private boolean storeIntoRegister(int seen, int reg) {
84 switch (seen) {
85 case ASTORE_0:
86 return reg == 0;
87 case ASTORE_1:
88 return reg == 1;
89 case ASTORE_2:
90 return reg == 2;
91 case ASTORE_3:
92 return reg == 3;
93 case ASTORE:
94 return reg == getRegisterOperand();
95 default:
96 return false;
97 }
98 }
99
100 @Override
101 public void sawOpcode(int seen) {
102 if (reportedThisMethod) return;
103 int oldState = state;
104 if (DEBUG) System.out.println("Opcode: " + OPCODE_NAMES[seen]);
105 switch (state) {
106 case SEEN_NOTHING:
107 if ((seen == NEW)
108 &&
109 getClassConstantOperand().startsWith("java/lang/StringBu")) {
110 state = SEEN_NEW;
111 createPC = getPC();
112 }
113 break;
114
115 case SEEN_NEW:
116 if (DEBUG && seen == INVOKEVIRTUAL) {
117 System.out.println("Invoke virtual");
118 System.out.println(" " + getNameConstantOperand());
119 System.out.println(" " + getClassConstantOperand());
120 System.out.println(" " + getSigConstantOperand());
121 }
122 if (seen == INVOKEVIRTUAL
123 && "append".equals(getNameConstantOperand())
124 && getClassConstantOperand().startsWith("java/lang/StringBu")) {
125 if (DEBUG) System.out.println("Saw string being appended from register " + registerOnStack);
126 if (getSigConstantOperand().startsWith("(Ljava/lang/String;)")
127 && registerOnStack >= 0) {
128 if (DEBUG)
129 System.out.println("Saw string being appended, source = " + registerOnStack);
130 state = SEEN_APPEND1;
131 stringSource = registerOnStack;
132 } else
133 reset();
134 }
135 break;
136 case SEEN_APPEND1:
137 if (storeIntoRegister(seen, stringSource))
138 reset();
139 else if (seen == INVOKEVIRTUAL
140 && "append".equals(getNameConstantOperand())
141 && getClassConstantOperand().startsWith("java/lang/StringBu")) {
142 state = SEEN_APPEND2;
143 }
144 break;
145
146 case SEEN_APPEND2:
147 if (storeIntoRegister(seen, stringSource))
148 reset();
149 else if (seen == INVOKEVIRTUAL
150 && "toString".equals(getNameConstantOperand())
151 && getClassConstantOperand().startsWith("java/lang/StringBu")) {
152 state = CONSTRUCTED_STRING_ON_STACK;
153 }
154 break;
155
156 case CONSTRUCTED_STRING_ON_STACK:
157 if (storeIntoRegister(seen, stringSource))
158 state = POSSIBLE_CASE;
159 else
160 reset();
161 break;
162
163 case POSSIBLE_CASE:
164 if (seen == GOTO
165 && (getPC() - getBranchTarget()) < 300
166 && getBranchTarget() < createPC) {
167 bugReporter.reportBug(new BugInstance(this, "SBSC_USE_STRINGBUFFER_CONCATENATION", NORMAL_PRIORITY)
168 .addClassAndMethod(this)
169 .addSourceLine(this, createPC));
170 reset();
172 reportedThisMethod = true;
173 } else if ((seen == NEW)
174 &&
175 getClassConstantOperand().startsWith("java/lang/StringBu")) {
176 state = SEEN_NEW;
177 createPC = getPC();
178 }
179 break;
180 }
181 registerOnStack = -1;
182 switch (seen) {
183 case ALOAD_0:
184 registerOnStack = 0;
185 break;
186 case ALOAD_1:
187 registerOnStack = 1;
188 break;
189 case ALOAD_2:
190 registerOnStack = 2;
191 break;
192 case ALOAD_3:
193 registerOnStack = 3;
194 break;
195 case ALOAD:
196 registerOnStack = getRegisterOperand();
197 break;
198 }
199 if (DEBUG && state != oldState)
200 System.out.println("At PC " + getPC()
201 + " changing from state " + oldState
202 + " to state " + state
203 + ", regOnStack = " + registerOnStack);
204 }
205 }
206
207 |
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