java class反编译后的代码还原（二）
java class 利用jad 反编译之后，偶尔回碰到一些不正常的代码，例如：label0 :_L1 MISSING_BLOCK_LABEL_30、JVM INSTR ret 7、JVM INSTR tableswitch 1 3: default 269、 JVM INSTR monitorexit、JVM INSTR monitorenter，这些一般是由特殊的for循环、try catch finally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。本文在Jdk 1.4.2_08+jad 1.58f下测试。jad 1.5.8f可以到这里http://download.csdn.net/source/470540 下载。
第二部分、异常
下面的代码前提是类中有如下属性， Calendar cal = Calendar.getInstance();。
1、Exceptioin的还原 反编译后的代码如下：
public boolean f1()
{
return cal.getTime().after(new Date());
Exception e;
e;
e.printStackTrace();
return false;
}
还原后的Java代码
public boolean f1()
{
try
{
return cal.getTime().after(new Date());
}
catch (Exception e)
{
e.printStackTrace();
return false;
}
}
2、finally代码的还原 反编译后的Java代码如下：
public boolean f2()
{
boolean flag = cal.getTime().after(new Date());
System.out.println("finally");
return flag;
Exception e;
e;
e.printStackTrace();
System.out.println("finally");
return false;
Exception exception;
exception;
System.out.println("finally");
throw exception;
}
还原后的代码如下：
public boolean f2()
{
try
{
return cal.getTime().after(new Date());
}
catch (Exception e)
{
e.printStackTrace();
return false;
}
finally
{
System.out.println("finally");
}
}
3、MISSING_BLOCK_LABEL_的还原反编译后的代码
public Object f22()
{
Date date = cal.getTime();
System.out.println("finally");
return date;
Exception e;
e;
e.printStackTrace();
System.out.println("finally");
break MISSING_BLOCK_LABEL_45;
Exception exception;
exception;
System.out.println("finally");
throw exception;
return null;
}
还原后的Java代码
public Object f22()
{
try
{
return cal.getTime();
}
catch (Exception e)
{
e.printStackTrace();
}
finally
{
System.out.println("finally");
}
return null;
}
4、异常中:label的还原反编译后的代码
public String f4()
throws Exception
{
label0:
{
try
{
Integer i = new Integer(1);
if(i.intValue() > 0)
{
System.out.println(i);
break label0;
}
System.err.println(i);
}
catch(Exception dae)
{
System.err.println(dae);
throw new RuntimeException(dae);
}
return null;
}
return "Hello";
}
注意，这个代码有点诡异，实际代码如下：
public String f4() throws Exception
{
try
{
Integer i = new Integer(1);
if (i.intValue() > 0)
{
System.out.println(i);
}
else
{
System.err.println(i);
return null;
}
return "Hello";
}
catch (Exception dae)
{
System.err.println(dae);
throw new RuntimeException(dae);
}
}
5、典型数据库操作代码还原 反编译后代码
public HashMap f5()
{
Connection conn = null;
HashMap hashmap;
HashMap map = new HashMap();
Class.forName("");
conn = DriverManager.getConnection("jdbc:odbc:");
PreparedStatement pstmt = conn.prepareStatement("select * from table");
pstmt.setString(1, "param");
String columnVallue;
for(ResultSet rs = pstmt.executeQuery(); rs.next(); map.put(columnVallue, ""))
columnVallue = rs.getString("column");
hashmap = map;
if(conn != null)
try
{
conn.close();
}
catch(SQLException sqlce)
{
sqlce.printStackTrace();
}
return hashmap;
ClassNotFoundException cnfe;
cnfe;
cnfe.printStackTrace();
if(conn != null)
try
{
conn.close();
}
catch(SQLException sqlce)
{
sqlce.printStackTrace();
}
break MISSING_BLOCK_LABEL_188;
SQLException sqle;
sqle;
sqle.printStackTrace();
if(conn != null)
try
{
conn.close();
}
catch(SQLException sqlce)
{
sqlce.printStackTrace();
}
break MISSING_BLOCK_LABEL_188;
Exception exception;
exception;
if(conn != null)
try
{
conn.close();
}
catch(SQLException sqlce)
{
sqlce.printStackTrace();
}
throw exception;
return null;
}
实际代码如下：
public HashMap f5()
{
Connection conn = null;
try
{
HashMap map = new HashMap();
Class.forName("");
conn = DriverManager.getConnection("jdbc:odbc:");
PreparedStatement pstmt = conn.prepareStatement("select * from table");
pstmt.setString(1, "param");
ResultSet rs = pstmt.executeQuery();
while (rs.next())
{
String columnVallue = rs.getString("column");
map.put(columnVallue, "");
}
return map;
}
catch (ClassNotFoundException cnfe)
{
cnfe.printStackTrace();
}
catch (SQLException sqle)
{
sqle.printStackTrace();
}
finally
{
if (conn != null)
{
try
{
conn.close();
}
catch (SQLException sqlce)
{
sqlce.printStackTrace();
}
}
}
return null;
}
6、两层异常嵌套代码还原 反编译后的代码
public int f6()
{
int i = cal.getTime().compareTo(new Date());
System.out.println("finally");
return i;
Exception e1;
e1;
e1.printStackTrace();
System.out.println("finally");
return -1;
Exception e2;
e2;
e2.printStackTrace();
System.out.println("finally");
return -2;
Exception exception;
exception;
System.out.println("finally");
throw exception;
}
实际代码
public int f6()
{
try
{
try
{
return cal.getTime().compareTo(new Date());
}
catch (Exception e1)
{
e1.printStackTrace();
return -1;
}
}
catch (Exception e2)
{
e2.printStackTrace();
return -2;
}
finally
{
System.out.println("finally");
}
}
7、非常诡异的代码 反编译后的代码
public int f7()
{
int i = cal.getTime().compareTo(new Date());
System.out.println("finally");
return i;
Exception e1;
e1;
e1.printStackTrace();
_L2:
System.out.println("finally");
return -1;
Exception e2;
e2;
e2.printStackTrace();
if(true) goto _L2; else goto _L1
_L1:
Exception exception;
exception;
System.out.println("finally");
throw exception;
}
原始代码
public int f7()
{
try
{
try
{
return cal.getTime().compareTo(new Date());
}
catch (Exception e1)
{
e1.printStackTrace();
return -1;
}
}
catch (Exception e2)
{
e2.printStackTrace();
return -1;
}
finally
{
System.out.println("finally");
}
}