java - 诡异的 Java 反射错误

Question

所以，问题来了。我试图在 Java 中使用反射来定义一种“ View ”类型，以便通过有序方法声明输出到 Excel 工作表。 (按数字排序)

从理论上讲，这应该可以正常工作，并且在一定程度上确实如此。

问题在于，反射(reflection)方法有时似乎是随机决定起作用的，而不是其他方法。它不会抛出异常，它会毫无困难地找到方法名称，但是一旦它执行 boolean 检查以检查该方法是否以适当的标记开头，它有时会在 j = 5 处停止。这是代码澄清方法:

public boolean objectWriter(List<Object> input, String sheetName, int startingRow, String tag){
    ArrayList<Object> myList = new ArrayList<>();
    jxl.write.Number number;
    Label label;

    //This is just an internal counter since we're using a for-each loop. 
    int j;
    try{
        for (int i = 0; i < input.size(); i++){
            j = 0;
            //we want to iterate over all of the available methods in the given class with reflection
            for (Method m: input.get(i).getClass().getMethods()){
                //Check to see if the method name has our requested tag, plus the appropriate counter
                //tacked on, and ZERO parameters, in our case.
                myLog.debug("this is our boolean check: " + m.getName().startsWith((tag + j)));
                if (m.getName().startsWith((tag + j))){
                    myLog.debug("m.getname inside: " + m.getName());
                    //Invoke the method, give it's return value to r (return)
                    final Object r = m.invoke(input.get(i));
                    //Since we defined in the requirements of this class that it must be a string
                    //those types of methods returned, this works just fine, just case it to
                    //String (Since String extends object) and call it a day. 
                    if (isNumeric((String)r)){
                        //if it's a number, make a number object out of it. 
                        number = new jxl.write.Number(j, startingRow + i
                        , Double.parseDouble((String)r)
                        , buildNumberFormat((String)r));

                        myList.add(number);
                    }else{
                        label = new Label(j,startingRow + i,(String)r);
                        myList.add(label);
                    }
                    j++;
                }
            }
        }
    }catch(IllegalAccessException | IllegalArgumentException | InvocationTargetException ex){
        myLog.error("There was an error working through the point class with reflection.", ex);
        return false;
    }
    boolean successfulWrite = myExcelWriter.writeInformation(myList, sheetName);
    myExcelWriter.resizeColumns(18, sheetName);
    return successfulWrite;

}

因此，正如您在上面所看到的，它会反射性地在方法名称中查找调用者定义的“标记”以及一个数字。所以如果我有一个类似的方法:

public String get0(){}
public String get1(){}
public String get2(){}

等等。等等，我给这个方法添加了“get”标签，它将按指定的顺序提取所有这三个方法。此外，它是在使用此特定方法的要求中定义的，其返回值全部为字符串，因此我很确定这不是问题。奇怪的是我不明白为什么 if (m.getName().startsWith((tag + j))) 行上的 boolean 检查会在 j=5 时开始失败 有时

无论如何，如果有人有任何想法，我将非常感激。我被困在这里了。

还值得注意的是，对于我提供的数据集，j=5 每次都会成为“else”子句。这对我来说不仅仅是巧合，但我看不出有什么问题。

编辑

如果我在 boolean 检查之前对 'm' 运行操作，它完全按预期工作的概率(提取所有正确枚举的方法等)也会显着增加(接近 99% 的工作)，这也是毫无值(value)的。例如我如何在实际语句之前打印出该 boolean 语句？这使得它几乎每次都能工作。但这肯定不是一个解决方案。

编辑#2按照要求，我继续将 println 移至调试日志，这是一个截断的版本，但它本质上重复了 29 次内的模式，也很有趣，似乎如果我将输出发送到记录器而不是控制台，前面提到的成功概率又回到了没有它的情况......奇怪......

09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,881 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: true
09:02:45,882 DEBUG [root] m.getname inside: xGet0Label
09:02:45,882 DEBUG [root] this is our boolean check: true
09:02:45,882 DEBUG [root] m.getname inside: xGet1MD
09:02:45,882 DEBUG [root] this is our boolean check: true
09:02:45,882 DEBUG [root] m.getname inside: xGet2Easting
09:02:45,882 DEBUG [root] this is our boolean check: true
09:02:45,882 DEBUG [root] m.getname inside: xGet3Northing
09:02:45,882 DEBUG [root] this is our boolean check: true
09:02:45,882 DEBUG [root] m.getname inside: xGet4TVD
09:02:45,882 DEBUG [root] this is our boolean check: true
09:02:45,882 DEBUG [root] m.getname inside: xGet5Date
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,882 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,883 DEBUG [root] this is our boolean check: false
09:02:45,884 DEBUG [root] this is our boolean check: false
09:02:45,884 DEBUG [root] this is our boolean check: false
09:02:45,884 DEBUG [root] this is our boolean check: false
09:02:45,884 DEBUG [root] this is our boolean check: false
09:02:45,884 DEBUG [root] this is our boolean check: true
09:02:45,884 DEBUG [root] m.getname inside: xGet0Label
09:02:45,884 DEBUG [root] this is our boolean check: true
09:02:45,884 DEBUG [root] m.getname inside: xGet1MD
09:02:45,884 DEBUG [root] this is our boolean check: true
09:02:45,884 DEBUG [root] m.getname inside: xGet2Easting
09:02:45,884 DEBUG [root] this is our boolean check: true
09:02:45,884 DEBUG [root] m.getname inside: xGet3Northing
09:02:45,884 DEBUG [root] this is our boolean check: true
09:02:45,884 DEBUG [root] m.getname inside: xGet4TVD
09:02:45,884 DEBUG [root] this is our boolean check: true
09:02:45,884 DEBUG [root] m.getname inside: xGet5Date

Answer 1

想通了!因此，我处理正在检查的方法的“顺序”的方式存在一个固有的错误。虽然我预计“getMethods()”会以不特定的顺序返回类的方法，但如果其中一个方法以错误的顺序出现，它永远不会被重新检查!只是偶然地，有时按数字顺序排列的第一个方法会出现在后面的方法之前，从而导致正确的行为。大多数情况下，编号方法 0-5 恰好出现在 6-14 之后(这是该数据集中的范围)。

所以，我的解决方案是创建一个被拒绝的方法名称“池”，然后每次检查失败时，迭代拒绝池，并确保其中一个也不符合要求。如果不是这些，那么它就不是我们关心的方法。

这会稍微减慢速度，但在毫秒范围内。

解决方案代码:

public boolean objectWriter(List<Object> input, String sheetName, int startingRow, String tag){
    ArrayList<Object> myList = new ArrayList<>();
    ArrayList<Method> methodList = new ArrayList<>();
    jxl.write.Number number;
    Label label;

    //This is just an internal counter since we're using a for-each loop. 
    int j;
    try{
        for (int i = 0; i < input.size(); i++){
            j = 0;
            //we want to iterate over all of the available methods in the given class with reflection
            for (Method m: input.get(i).getClass().getDeclaredMethods()){
                //Check to see if the method name has our requested tag, plus the appropriate counter
                //tacked on, and ZERO parameters, in our case.
                if (m.getName().startsWith((tag + j))){
                    //Invoke the method, give it's return value to r (return)
                    final Object r = m.invoke(input.get(i));
                    //Since we defined in the requirements of this class that it must be a string
                    //those types of methods returned, this works just fine, just case it to
                    //String (Since String extends object) and call it a day. 
                    if (isNumeric((String)r)){
                        //if it's a number, make a number object out of it. 
                        number = new jxl.write.Number(j, startingRow + i
                        , Double.parseDouble((String)r)
                        , buildNumberFormat((String)r));

                        myList.add(number);
                    }else{
                        label = new Label(j,startingRow + i,(String)r);
                        myList.add(label);
                    }
                    j++;
                }else{
                    methodList.add(m);
                    for (int x = 0; x < methodList.size(); x++){
                        if (methodList.get(x).getName().startsWith((tag + j))){
                            //Invoke the method, give it's return value to r (return)
                            final Object r = methodList.get(x).invoke(input.get(i));
                            //Since we defined in the requirements of this class that it must be a string
                            //those types of methods returned, this works just fine, just case it to
                            //String (Since String extends object) and call it a day. 
                            if (isNumeric((String)r)){
                                //if it's a number, make a number object out of it. 
                                number = new jxl.write.Number(j, startingRow + i
                                , Double.parseDouble((String)r)
                                , buildNumberFormat((String)r));

                                myList.add(number);
                            }else{
                                label = new Label(j,startingRow + i,(String)r);
                                myList.add(label);
                            }
                            j++;
                            //methodList.remove(x);
                            break;
                        }
                    }
                }
            }
        }
    }catch(IllegalAccessException | IllegalArgumentException | InvocationTargetException ex){
        myLog.error("There was an error working through the point class with reflection.", ex);
        return false;
    }
    boolean successfulWrite = myExcelWriter.writeInformation(myList, sheetName);
    myExcelWriter.resizeColumns(18, sheetName);
    return successfulWrite;

}

这是一个很好的教训，当您尝试对本质上无序的列表强加顺序时，请确保您小心，因为如果您把它搞砸了(像我一样!)，它会感觉像是非常未定义的行为。