android反编译apk后，java文件中出现的一些类似乱码的问题

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概述

java class  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。

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");} }