javaclass反编译后的代码还原

1、javaclass利用jad反编译之后，偶尔回碰到一些不正常的代码，例如：labelO:丄1MISSING_BLOCK_LABEL_30、JVMINSTRret7、JVMINSTRtableswitch13:default269、JVMINSTRmonitorexit、JVMINSTRmonitorenter，这些一般是由特殊的for循环、trycatchfinally语句块、synchronized语句反编译后产生的。下面，就简单介绍一下，一些反编译后的特殊代码的还原规则。异常下面的代码前提是类中有如下属性，Calendarcal=Calendar.getInstance();1、Excep

2、tioin的还原反编译后的代码如下：publicbooleanf1()returncal.getTime().after(newDate();Exceptione;e;e.printStackTrace();returnfalse;还原后的Java代码publicbooleanf1()tryreturncal.getTime().after(newDate();catch(Exceptione)e.printStackTrace();returnfalse;2、finally代码的还原反编译后的Java代码如下：publicbooleanf2()booleanflag=cal.getTime(

3、).after(newDate();System.out.println(finally);returnflag;Exceptione;e;e.printStackTrace();System.out.println(finally);returnfalse;Exceptionexception;exception;System.out.println(finally);throwexception;还原后的代码如下：publicbooleanf2()tryreturncal.getTime().after(newDate();catch(Exceptione)e.printStackTrac

4、e();returnfalse;finallySystem.out.println(finally);3、MISSING_BLOCK_LABEL_的还原反编译后的代码publicObjectf22()Datedate=cal.getTime();System.out.println(finally);returndate;Exceptione;e;e.printStackTrace();System.out.println(finally);breakMISSING_BLOCK_LABEL_45;Exceptionexception;exception;System.out.println(f

5、inally);throwexception;returnnull;还原后的Java代码publicObjectf22()tryreturncal.getTime();catch(Exceptione)e.printStackTrace();finallySystem.out.println(finally);returnnull;4、异常中:label的还原反编译后的代码publicStringf4()throwsExceptionlabelO:tryIntegeri=newInteger(1);if(Value()O)System.out.println(i);breaklabelO;Sy

6、stem.err.println(i);catch(Exceptiondae)System.err.println(dae);thrownewRuntimeException(dae);returnnull;returnHello;注意，这个代码有点诡异，实际代码如下：publicStringf4()throwsExceptiontryIntegeri=newInteger(1);if(Value()O)System.out.println(i);elseSystem.err.println(i);returnnull;returnHello;catch(Exceptiondae)System

7、.err.println(dae);thrownewRuntimeException(dae);5、典型数据库操作代码还原反编译后代码publicHashMapf5()Connectionconn=null;HashMaphashmap;HashMapmap=newHashMap();Class.forName();conn=DriverManager.getConnection(jdbc:odbc:);PreparedStatementpstmt=conn.prepareStatement(select*fromtable);pstmt.setString(1,param);Stringco

8、lumnVallue;for(ResultSetrs=pstmt.executeQuery();rs.next();map.put(columnVallue,)columnVallue=rs.getString(column);hashmap=map;if(conn!=null)tryconn.close();catch(SQLExceptionsqlce)sqlce.printStackTrace();returnhashmap;ClassNotFoundExceptioncnfe;cnfe;cnfe.printStackTrace();if(conn!=null)tryconn.close

9、();catch(SQLExceptionsqlce)sqlce.printStackTrace();breakMISSING_BLOCK_LABEL_188;SQLExceptionsqle;sqle;sqle.printStackTrace();if(conn!=null)tryconn.close();catch(SQLExceptionsqlce)sqlce.printStackTrace();breakMISSING_BLOCK_LABEL_188;Exceptionexception;exception;if(conn!=null)tryconn.close();catch(SQL

10、Exceptionsqlce)sqlce.printStackTrace();throwexception;returnnull;实际代码如下：publicHashMapf5()Connectionconn=null;tryHashMapmap=newHashMap();Class.forName();conn=DriverManager.getConnection(jdbc:odbc:);PreparedStatementpstmt=conn.prepareStatement(select*fromtable);pstmt.setString(1,param);ResultSetrs=pst

11、mt.executeQuery();while(rs.next()StringcolumnVallue=rs.getString(column);map.put(columnVallue,);returnmap;catch(ClassNotFoundExceptioncnfe)cnfe.printStackTrace();catch(SQLExceptionsqle)sqle.printStackTrace();finallyif(conn!=null)tryconn.close();catch(SQLExceptionsqlce)sqlce.printStackTrace();returnn

12、ull;6、两层异常嵌套代码还原反编译后的代码publicintf6()inti=cal.getTime().compareTo(newDate();System.out.println(finally);returni;Exceptione1;e1;e1.printStackTrace();System.out.println(finally);return-1;Exceptione2;e2;e2.printStackTrace();System.out.println(finally);return-2;Exceptionexception;exception;System.out.pri

13、ntln(finally);throwexception;实际代码publicintf6()trytryreturncal.getTime().compareTo(newDate();catch(Exceptione1)e1.printStackTrace();return-1;catch(Exceptione2)e2.printStackTrace();return-2;finallySystem.out.println(finally);7、非常诡异的代码反编译后的代码publicintf7()inti=cal.getTime().compareTo(newDate();System.out.println(finally);returni;Exceptione1;e1;e1.printStackTrace();_L2:System.out.println(finally);return-1;Exceptione2;e2;e2.printStackTrace();if(true)goto_L2;elsegoto_L1_L1:Exceptionexception;exception;System.out.println(fi