1

我修改了对象转储方法以避免循环引用导致 StackOverflow 错误。这就是我最终的结果:

//returns all fields of the given object in a string
 public static String dumpFields(Object o, int callCount, ArrayList excludeList)
 {
  //add this object to the exclude list to avoid circual references in the future
  if (excludeList == null) excludeList = new ArrayList();
  excludeList.add(o);

  callCount++;
  StringBuffer tabs = new StringBuffer();
  for (int k = 0; k < callCount; k++)
  {
   tabs.append("\t");
  }
  StringBuffer buffer = new StringBuffer();
  Class oClass = o.getClass();
  if (oClass.isArray()) {   
   buffer.append("\n");
   buffer.append(tabs.toString());
   buffer.append("[");
   for (int i = 0; i < Array.getLength(o); i++)
   {
    if (i < 0) buffer.append(",");
    Object value = Array.get(o, i);

    if (value != null)
    {
     if (excludeList.contains(value))
     {
      buffer.append("circular reference");
     }
     else if (value.getClass().isPrimitive() || value.getClass() == java.lang.Long.class || value.getClass() == java.lang.String.class || value.getClass() == java.lang.Integer.class || value.getClass() == java.lang.Boolean.class)
     {
      buffer.append(value);
     }
     else
     {
      buffer.append(dumpFields(value, callCount, excludeList));
     }
    }
   }
   buffer.append(tabs.toString());
   buffer.append("]\n");
  }
  else
  {   
   buffer.append("\n");
   buffer.append(tabs.toString());
   buffer.append("{\n");
   while (oClass != null)
   {    
    Field[] fields = oClass.getDeclaredFields();
    for (int i = 0; i < fields.length; i++)
    {
     if (fields[i] == null) continue;

     buffer.append(tabs.toString());
     fields[i].setAccessible(true);
     buffer.append(fields[i].getName());
     buffer.append("=");
     try
     {
      Object value = fields[i].get(o);
      if (value != null)
      {
       if (excludeList.contains(value))
       {
        buffer.append("circular reference");
       }
       else if ((value.getClass().isPrimitive()) || (value.getClass() == java.lang.Long.class) || (value.getClass() == java.lang.String.class) || (value.getClass() == java.lang.Integer.class) || (value.getClass() == java.lang.Boolean.class))
       {
        buffer.append(value);
       }
       else
       {
        buffer.append(dumpFields(value, callCount, excludeList));
       }
      }
     }
     catch (IllegalAccessException e)
     {
      System.out.println("IllegalAccessException: " + e.getMessage());
     }
     buffer.append("\n");
    }
    oClass = oClass.getSuperclass();
   }
   buffer.append(tabs.toString());
   buffer.append("}\n");
  }
  return buffer.toString();
 }

该方法最初是这样调用的:

System.out.println(dumpFields(obj, 0, null);

所以,基本上我添加了一个 excludeList ,其中包含所有之前检查过的对象。现在,如果一个对象包含另一个对象并且该对象链接回原始对象,则它不应该沿着该链进一步跟随该对象。

但是,我的逻辑似乎有缺陷,因为我仍然陷入无限循环。有谁知道为什么会这样?

编辑:

我仍然收到 StackOverflow 错误

Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
    at java.lang.reflect.Field.copy(Field.java:127)
    at java.lang.reflect.ReflectAccess.copyField(ReflectAccess.java:122)
    at sun.reflect.ReflectionFactory.copyField(ReflectionFactory.java:289)
    at java.lang.Class.copyFields(Class.java:2739)
    at java.lang.Class.getDeclaredFields(Class.java:1743)
    at com.gui.ClassName.dumpFields(ClassName.java:627)

我更新的方法:

public static String dumpFields(Object o, int callCount, IdentityHashMap idHashMap)
    {
        callCount++;

        //add this object to the exclude list to avoid circual references in the future
        if (idHashMap == null) idHashMap = new IdentityHashMap();
        idHashMap.put(o, o);

        //setup string buffer and add fields
        StringBuffer tabs = new StringBuffer();
        for (int k = 0; k < callCount; k++)
        {
            tabs.append("\t");
        }
        StringBuffer buffer = new StringBuffer();
        Class oClass = o.getClass();
        if (oClass.isArray()) {         
            buffer.append("\n");
            buffer.append(tabs.toString());
            buffer.append("[");
            for (int i = 0; i < Array.getLength(o); i++)
            {
                if (i < 0) buffer.append(",");
                Object value = Array.get(o, i);

                if (value != null)
                {
                    if (idHashMap.containsKey(value))
                    {
                        buffer.append("circular reference");
                    }
                    else if (value.getClass().isPrimitive() || value.getClass() == java.lang.Long.class || value.getClass() == java.lang.String.class || value.getClass() == java.lang.Integer.class || value.getClass() == java.lang.Boolean.class)
                    {
                        buffer.append(value);
                    }
                    else
                    {
                        buffer.append(dumpFields(value, callCount, idHashMap));
                    }
                }
            }
            buffer.append(tabs.toString());
            buffer.append("]\n");
        }
        else
        {           
            buffer.append("\n");
            buffer.append(tabs.toString());
            buffer.append("{\n");
            while (oClass != null)
            {               
                Field[] fields = oClass.getDeclaredFields();
                for (int i = 0; i < fields.length; i++)
                {
                    if (fields[i] == null) continue;

                    buffer.append(tabs.toString());
                    fields[i].setAccessible(true);
                    buffer.append(fields[i].getName());
                    buffer.append("=");
                    try
                    {
                        Object value = fields[i].get(o);
                        if (value != null)
                        {
                            if (idHashMap.containsKey(value))
                            {
                                buffer.append("circular reference");
                            }
                            else if ((value.getClass().isPrimitive()) || (value.getClass() == java.lang.Long.class) || (value.getClass() == java.lang.String.class) || (value.getClass() == java.lang.Integer.class) || (value.getClass() == java.lang.Boolean.class))
                            {
                                buffer.append(value);
                            }
                            else
                            {
                                buffer.append(dumpFields(value, callCount, idHashMap));
                            }
                        }
                    }
                    catch (IllegalAccessException e)
                    {
                        System.out.println("IllegalAccessException: " + e.getMessage());
                    }
                    buffer.append("\n");
                }
                oClass = oClass.getSuperclass();
            }
            buffer.append(tabs.toString());
            buffer.append("}\n");
        }
        return buffer.toString();
    }

编辑2:

您的解决方案似乎非常好。不幸的是,即使我只在一个只有 4 个字段的小类上使用过它,我现在也遇到了 OutOfMemory 错误。这是我最终得到的代码:

//returns all fields of the given object in a string
    public static String dumpFields(Object start)
    {
        class CallLevel
        {
            public Object target;
            public int level;

            public CallLevel(Object target, int level)
            {
                this.target = target;
                this.level = level;
            }
        }

        //create a work list
        List<CallLevel> workList = new ArrayList<CallLevel>();
        workList.add(new CallLevel(start, 0));

        //add this object to the exclude list to avoid circual references in the future
        IdentityHashMap idHashMap = new IdentityHashMap();

        StringBuffer buffer = new StringBuffer();
        while (!workList.isEmpty())
        {
            CallLevel level = workList.remove(workList.size() - 1);
            Object o = level.target;

            //add this object to the exclude list to avoid circual references in the future
            idHashMap.put(o, o);

            //setup string buffer and add fields
            StringBuffer tabs = new StringBuffer();
            int callCount = level.level;
            for (int k = 0; k < callCount; k++)
            {
                tabs.append("\t");
            }
            callCount++;
            Class oClass = o.getClass();

            if (oClass.isArray()) {         
                buffer.append("\n");
                buffer.append(tabs.toString());
                buffer.append("[");
                for (int i = 0; i < Array.getLength(o); i++)
                {
                    if (i < 0) buffer.append(",");
                    Object value = Array.get(o, i);

                    if (value != null)
                    {
                        if (idHashMap.containsKey(value))
                        {
                            buffer.append("circular reference");
                        }
                        else if (value.getClass().isPrimitive() || value.getClass() == java.lang.Long.class || value.getClass() == java.lang.String.class || value.getClass() == java.lang.Integer.class || value.getClass() == java.lang.Boolean.class)
                        {
                            buffer.append(value);
                        }
                        else
                        {
                            workList.add(new CallLevel(value, callCount));
                        }
                    }
                }
                buffer.append(tabs.toString());
                buffer.append("]\n");
            }
            else
            {           
                buffer.append("\n");
                buffer.append(tabs.toString());
                buffer.append("{\n");
                while (oClass != null)
                {               
                    Field[] fields = oClass.getDeclaredFields();
                    for (int i = 0; i < fields.length; i++)
                    {
                        if (fields[i] == null) continue;

                        buffer.append(tabs.toString());
                        fields[i].setAccessible(true);
                        buffer.append(fields[i].getName());
                        buffer.append("=");
                        try
                        {
                            Object value = fields[i].get(o);
                            if (value != null)
                            {
                                if (idHashMap.containsKey(value))
                                {
                                    buffer.append("circular reference");
                                }
                                else if ((value.getClass().isPrimitive()) || (value.getClass() == java.lang.Long.class) || (value.getClass() == java.lang.String.class) || (value.getClass() == java.lang.Integer.class) || (value.getClass() == java.lang.Boolean.class))
                                {
                                    buffer.append(value);
                                }
                                else
                                {
                                    workList.add(new CallLevel(value, callCount));
                                }
                            }
                        }
                        catch (IllegalAccessException e)
                        {
                            System.out.println("IllegalAccessException: " + e.getMessage());
                        }
                        buffer.append("\n");
                    }
                    oClass = oClass.getSuperclass();
                }
                buffer.append(tabs.toString());
                buffer.append("}\n");
            }
        }
        return buffer.toString();
    }

这么小的对象不应该导致 OutOfMemory 错误。

有任何想法吗?

编辑3:

改写版:

public static String dumpFields(Object start)
    {
        class CallLevel
        {
            public Object target;
            public int level;

            public CallLevel(Object target, int level)
            {
                this.target = target;
                this.level = level;
            }
        }

        //create a work list
        List<CallLevel> workList = new ArrayList<CallLevel>();
        workList.add(new CallLevel(start, 0));

        //create an identity map for object comparison
        IdentityHashMap idHashMap = new IdentityHashMap();

        //setup a string buffer to return
        StringBuffer buffer = new StringBuffer();
        while (!workList.isEmpty())
        {
            CallLevel level = workList.remove(workList.size() - 1);
            Object o = level.target;

            //add this object to the exclude list to avoid circual references in the future
            idHashMap.put(o, o);

            //set string buffer for tabs
            StringBuffer tabs = new StringBuffer();
            int callCount = level.level;
            for (int k = 0; k < callCount; k++)
            {
                tabs.append("\t");
            }

            //increment the call count for future calls
            callCount++;

            //set the class for this object
            Class oClass = o.getClass();

            //if this is an array, dump it's elements, otherwise dump the fields of this object
            if (oClass.isArray()) {         
                buffer.append("\n");
                buffer.append(tabs.toString());
                buffer.append("[");
                for (int i = 0; i < Array.getLength(o); i++)
                {
                    if (i < 0) buffer.append(",");
                    Object value = Array.get(o, i);

                    if (value != null)
                    {
                        if (value.getClass().isPrimitive())
                        {
                            buffer.append(value);
                        }
                        else if (idHashMap.containsKey(value))
                        {
                            buffer.append("circular reference");
                        }
                        else
                        {
                            workList.add(new CallLevel(value, callCount));
                        }
                    }
                }
                buffer.append(tabs.toString());
                buffer.append("]\n");
            }
            else
            {           
                buffer.append("\n");
                buffer.append(tabs.toString());
                buffer.append("{\n");
                while (oClass != null)
                {               
                    Field[] fields = oClass.getDeclaredFields();
                    for (int i = 0; i < fields.length; i++)
                    {
                        //make sure this field exists
                        if (fields[i] == null) continue;

                        //ignore static fields
                        if (!Modifier.isStatic(fields[i].getModifiers()))
                        {
                            buffer.append(tabs.toString());
                            fields[i].setAccessible(true);
                            buffer.append(fields[i].getName());
                            buffer.append("=");
                            try
                            {
                                Object value = fields[i].get(o);
                                if (value != null)
                                {
                                    if (fields[i].getType().isPrimitive())
                                    {
                                        buffer.append(value);
                                    }
                                    else if (idHashMap.containsKey(value))
                                    {
                                        buffer.append("circular reference");
                                    }
                                    else
                                    {
                                        workList.add(new CallLevel(value, callCount));
                                    }
                                }
                            }
                            catch (IllegalAccessException e)
                            {
                                System.out.println("IllegalAccessException: " + e.getMessage());
                            }
                            buffer.append("\n");
                        }
                    }
                    oClass = oClass.getSuperclass();
                }
                buffer.append(tabs.toString());
                buffer.append("}\n");
            }   
        }
        return buffer.toString();
    }

我假设 getClass().isPrimitive() 仍然适用于数组索引,但我可能错了。如果是这样,您将如何处理?此外,其他 getClass() == Integer 等检查对我来说似乎是不必要的,因为 isPrimitive() 检查应该解决这个问题,对吧?

无论如何,在一个简单的对象上使用时,我仍然会遇到内存不足错误:

Exception in thread "AWT-EventQueue-0" java.lang.OutOfMemoryError: Java heap space
    at java.util.Arrays.copyOfRange(Arrays.java:3209)
    at java.lang.String.<init>(String.java:215)
    at java.lang.StringBuffer.toString(StringBuffer.java:585)
    at com.gui.ClassName.dumpFields(ClassName.java:702)
    at com.gui.ClassName.setTextArea(ClassName.java:274)
    at com.gui.ClassName.access$8(ClassName.java:272)
    at com.gui.ClassName$1.valueChanged(ClassName.java:154)
    at javax.swing.JList.fireSelectionValueChanged(JList.java:1765)
    at javax.swing.JList$ListSelectionHandler.valueChanged(JList.java:1779)
    at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:167)
    at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:147)
    at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:194)
    at javax.swing.DefaultListSelectionModel.changeSelection(DefaultListSelectionModel.java:388)
    at javax.swing.DefaultListSelectionModel.changeSelection(DefaultListSelectionModel.java:398)
    at javax.swing.DefaultListSelectionModel.setSelectionInterval(DefaultListSelectionModel.java:442)
    at javax.swing.JList.setSelectedIndex(JList.java:2179)
    at com.gui.ClassName$1.valueChanged(ClassName.java:138)
    at javax.swing.JList.fireSelectionValueChanged(JList.java:1765)
    at javax.swing.JList$ListSelectionHandler.valueChanged(JList.java:1779)
    at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:167)
    at javax.swing.DefaultListSelectionModel.fireValueChanged(DefaultListSelectionModel.java:137)
    at javax.swing.DefaultListSelectionModel.setValueIsAdjusting(DefaultListSelectionModel.java:668)
    at javax.swing.JList.setValueIsAdjusting(JList.java:2110)
    at javax.swing.plaf.basic.BasicListUI$Handler.mouseReleased(BasicListUI.java:2783)
    at java.awt.AWTEventMulticaster.mouseReleased(AWTEventMulticaster.java:273)
    at java.awt.Component.processMouseEvent(Component.java:6263)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3255)
    at java.awt.Component.processEvent(Component.java:6028)
    at java.awt.Container.processEvent(Container.java:2041)
    at java.awt.Component.dispatchEventImpl(Component.java:4630)
    at java.awt.Container.dispatchEventImpl(Container.java:2099)
    at java.awt.Component.dispatchEvent(Component.java:4460)
4

1 回答 1

4

+1 用于IdentityHashMap解决问题。

原因是您的方法当前取决于每个访问对象的类如何实现equals,因为List.contains(Object)用作equals比较的基础。如果一个类的equals()方法被破坏,并且false即使将自身作为比较对象传递也错误地返回,那么您将得到一个无限循环,因为调用List.contains总是返回 false 并且该对象子图总是针对该类型的对象进行遍历。

此外,如果您有两个或多个对象是不同的实例,但在值上被认为是相等的(即 equals 返回 true),则只会写出其中一个。这是可取的还是问题取决于您的用例。

使用 anIdentityHashMap将避免这两个问题。

顺便说一句 - 如果您想根据调用深度缩进,请不要忘记callCount在递归调用时递增dumpFields.

编辑:我认为代码工作正常。问题是您确实遇到了堆栈溢出。如果您有一个大型对象图,就会发生这种情况。例如,想象一个包含 3000 个元素的链表。这将涉及 3000 次递归调用,我很确定这会破坏默认堆栈大小的堆栈。

要解决此问题,您可以将堆栈的大小 (vmarg -Xss) 增加到足够大以处理您预期的对象图大小(不是一个强大的解决方案!),或者用显式数据结构替换堆栈的使用。

而不是堆栈,创建一个工作列表。此列表包含您已经看到但尚未处理的对象。您只需将对象添加到您的工作列表中,而不是递归调用 dumpFields。该方法的主体是一个 while 循环,只要列表中有项目,它就会迭代。

例如

class CallLevel
{
    CallLevel(Object target, int level) {
        this.target = target; this.level = level;
    }
    Object target;
    int level;
}
public static String dumpFields(Object start)
{
    List<CallLevel> workList = new ArrayList<CallLevel>();
    workList.add(new Calllevel(start,0));
    Map idHashMap = new IdentityHashMap();

    while (!workList.isEmpty()) {
        CallLevel level = workList.removeAt(workList.size()-1);
        Object o = level.object;
    //add this object to the exclude list to avoid circual references in the future
    idHashMap.put(, o);

    //setup string buffer and add fields
    StringBuffer tabs = new StringBuffer();
    int callCount = level.level;
    for (int k = 0; k < callCount; k++)
    {
        tabs.append("\t");
    }
    callCount++;
    StringBuffer buffer = new StringBuffer();
    Class oClass = o.getClass();
    if (oClass.isArray()) {         
        buffer.append("\n");
        buffer.append(tabs.toString());
        buffer.append("[");
        for (int i = 0; i < Array.getLength(o); i++)
        {
            if (i < 0) buffer.append(",");
            Object value = Array.get(o, i);

            if (value != null)
            {
                if (idHashMap.containsKey(value))
                {
                    buffer.append("circular reference");
                }
                else if (value.getClass().isPrimitive() || value.getClass() == java.lang.Long.class || value.getClass() == java.lang.String.class || value.getClass() == java.lang.Integer.class || value.getClass() == java.lang.Boolean.class)
                {
                    buffer.append(value);
                }
                else
                {
                    workList.add(new Calllevel(value, callCount));
                }
            }
        }
        buffer.append(tabs.toString());
        buffer.append("]\n");
    }
    else
    {           
        buffer.append("\n");
        buffer.append(tabs.toString());
        buffer.append("{\n");
        while (oClass != null)
        {               
            Field[] fields = oClass.getDeclaredFields();
            for (int i = 0; i < fields.length; i++)
            {
                if (fields[i] == null) continue;

                buffer.append(tabs.toString());
                fields[i].setAccessible(true);
                buffer.append(fields[i].getName());
                buffer.append("=");
                try
                {
                    Object value = fields[i].get(o);
                    if (value != null)
                    {
                        if (idHashMap.containsKey(value))
                        {
                            buffer.append("circular reference");
                        }
                        else if ((value.getClass().isPrimitive()) || (value.getClass() == java.lang.Long.class) || (value.getClass() == java.lang.String.class) || (value.getClass() == java.lang.Integer.class) || (value.getClass() == java.lang.Boolean.class))
                        {
                            buffer.append(value);
                        }
                        else
                        {
                            workList.add(new CallLevel(value, callCount));
                        }
                    }
                }
                catch (IllegalAccessException e)
                {
                    System.out.println("IllegalAccessException: " + e.getMessage());
                }
                buffer.append("\n");
            }
            oClass = oClass.getSuperclass();
        }
        buffer.append(tabs.toString());
        buffer.append("}\n");
    }
    return buffer.toString();

EDIT2:我刚刚运行了代码,看看会发生什么。完成这项工作需要进行 3 项主要更改:

  1. 原始类型的测试应该是第一个测试(3 个 if 语句中的第一个)。第二个 else if 是针对排除映射的测试。
  2. 原始类型的测试需要包括对所有原始类的检查。您目前有一些测试,但缺少浮点、双精度、字节、短和长。
  3. 跳过静态字段,检查Modifier.isStatic(field.getModifiers()).

原始测试应该首先发生的原因是,通过反射,原始类型使用相应类的新实例进行装箱(例如,对于双字段,创建一个新实例Double- 这是一种简化 - JDK 实际上会重用一些对象,请参阅Integer.valueOf()当一个基元被装箱时,通常会创建一个新对象的源。)由于这些基元生成唯一的新对象,因此根据排除映射检查这些几乎没有意义。因此,将primite测试放在首位。顺便说一句,检查value.getClass().isPrimitive()将始终返回 false - 装箱类型绝不是原始类型。您可以改为使用声明的字段类型,例如field.getType().isPrimitive().

针对盒装原语类的测试必须包括对所有盒装原语类的测试。如果没有,那么这些新的装箱对象将继续创建,发现尚未被排除(因为它们是新实例)并添加到工作列表中。这成为一个失控的问题 - 像 MAX_VALUE 这样的静态公共最终常量会导致生成更多实例,这些实例被添加到列表中,并且这些对象的字段的反射会导致更多值等......修复是确保所有原始类型都是测试(或在字段类型上使用 isPrimitive,而不是返回的对象类型。)

不输出静态字段将作为上述问题的辅助解决方案,但更重要的是,它将避免您的输出因不必要的细节而变得混乱。

于 2010-04-30T19:23:50.343 回答