java class反编译后的代码还原

javaclass利用jad反编译之后，偶尔回碰到一些不正常的代码，例如：label0:_L1MISSING_BLOCK_LABEL_30、JVM INSTR ret7、JVM INSTR tableswitch 1 3: default269、JVM INSTR monitorexit、JVM INSTR monitorenter，这些一般是由特殊的for循环、try catchfinally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：publicbooleanf2(){booleanflag=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publicObjectf22(){Datedate=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publicStringf4()throwsException{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 { Integeri = 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;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 (SQLException sqle) { sqle.printStackTrace();} finally { if (conn != null) { try { conn.close();} catch (SQLException sqlce) { sqlce.printStackTrace();} } } return null;}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;1.printStackTrace();return -1;} } catch (Exception e2) { e2.printStackTrace();return -2;} finally { System.out.println("finally");} }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;1.printStackTrace();return -1;} } catch (Exception e2) { e2.printStackTrace();return -1;} finally { System.out.println("finally"); } }。