直接转为数组遍历判断

    public int StrToInt(String str) {
        if(str == null || str.length() == 0)return 0;
        char[] arr = str.toCharArray();
        boolean negative = true;
        int res = 0;
        for(int i = 0;i<arr.length;i++){
            if(arr[i]>='0' && arr[i]<='9'){
                //判断溢出
                int cur = Character.digit(arr[i],10);
                if(negative&& (res > Integer.MAX_VALUE/10 || res == Integer.MAX_VALUE/10 && cur >7)){
                    return 0;
                }
                if(!negative&& (res > Integer.MAX_VALUE/10 || res == Integer.MAX_VALUE/10 && cur >8)){
                    return 0;
                }
                res  = res*10 + cur;
            }else if(arr[i] =='+'){
                negative = true;
            }else if(arr[i] == '-'){
                negative = false;
            }else{
                return 0;
            }
        }
        return negative ? res : -res;
    }