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");
}
}