java_class反编译后的代码还原

 

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。

 

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");
	} 
}