在 java 中处理大字符串时，StringBuilder 内存不足错误

Question

我从String test += str; 其中test以成千上万个字符呈指数级增长。 运行需要 45 分钟，可能是因为创建大字符串和删除垃圾。 然后我像这样交错输入，使其达到 30 秒。

这似乎是一种廉价的方法，但效果很好：

  if (secondDump.length() > 50)
  {
     intermedDump = intermedDump + secondDump;
     secondDump = "";
  }      

  if (intermedDump.length() > 100)
  {
     thirdDump = thirdDump + intermedDump;
     intermedDump = "";
  }
  if (thirdDump.length() > 500)
  {
     fourthDump = fourthDump + thirdDump;
     thirdDump = "";
  }
  if (fourthDump.length() > 1000)
  {
     fifthDump = fifthDump + fourthDump;
     fourthDump = "";
  }
  //with just this and not sixth.  Runtime>>>> : 77343
  if (fifthDump.length() > 5000)
  {
     sixthDump = sixthDump + fifthDump;
     fifthDump = "";
  }
  //with just this.  Runtime>>>> : 35903Runtime>>>> : 33780
  if (sixthDump.length() > 10000)
  {
     fillerDump = fillerDump + sixthDump;
     sixthDump = "";
  }

然后我发现StringBuilder存在，并且我一直在尝试使用它，用它替换所有字符串操作。

问题是，我不断收到java.lang.OutOfMemoryError和 java 内存堆溢出。 我认为该字符串太长而无法作为StringBuilder对象存储在内存中，因为它的进度大约是我之前的代码在因内存不足错误而崩溃之前所做的进度的 1/50。 它只能处理可能不到一千个字符。

为什么一个字符串可以保存整个输出而这不能接近？ 另外，如果我将文本附加到JTextPane ，那需要多少内存？ 如果我将StringBuilder内容转储到JTextpane并继续附加和清除似乎也不起作用的StringBuilder 。

这是现有的代码。 Page 只是一个被传递的对象：

protected void concatPlates(page PageA) throws IOException
{
   if (backend.isFirstPage == false)
   {
      frontend.fillOutputPane("\n                                 " +
         "                                               \n", PageA);
      frontend.fillOutputPane("                                 " +
         "                                               \n", PageA);
      frontend.fillOutputPane("                                 " +
         "                                               \n", PageA);
   }
   for (int i = 0; i < PLATELEN-1; i++)
   {

      if (arrLeftCol[i].length() == 0)
      {
         /////////////////////////////////////////////////////////
         /////////////////////////////////////////////////////////
         frontend.fillOutputPane(arrLeftCol[i].append(
           arrRightCol[i]));
      }
     else
     {
        PageA.tempStrBuff = new StringBuilder(arrLeftCol[i].substring(0,40));
        frontend.fillOutputPane(PageA.tempStrBuff.append(arrRightCol[i]));
     }
     arrLeftCol[i].append("");
     arrRightCol[i].append("");

     backend.isFirstPage = false;
  }
}


//this is the frontend class
public static void fillOutputPane(String s, page PageA)
{
   fillOutputPane(PageA.getStrBuf());
}
public static void fillOutputPane(StringBuilder stringBuild)
{
  try
  {
     str.append(stringBuild);
  }
  catch (java.lang.OutOfMemoryError e)
  {
     System.out.println((str.length() * 16) /8);
     //System.out.println(str);
     System.out.println("out of memory error");
     System.exit(0);
  }
}

这是错误：

Exception in thread "AWT-EventQueue-0" java.lang.OutOfMemoryError: Java heap space
at java.util.Arrays.copyOf(Unknown Source)
at java.lang.AbstractStringBuilder.expandCapacity(Unknown Source)
at java.lang.AbstractStringBuilder.append(Unknown Source)
at java.lang.StringBuilder.append(Unknown Source)
at java.lang.StringBuilder.append(Unknown Source)
at backend.fill(backend.java:603)
at frontend$openL.actionPerformed(frontend.java:191)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.AbstractButton.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)

我认为这就是堆栈跟踪：

java.lang.Exception: Stack trace
at java.lang.Thread.dumpStack(Unknown Source)
at frontend.fillOutputPane(frontend.java:385)
at page.concatPlates(page.java:105)
at backend.setPlate(backend.java:77)
at backend.fill(backend.java:257)
at frontend$openL.actionPerformed(frontend.java:191)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.AbstractButton.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI.doClick(Unknown Source)
at javax.swing.plaf.basic.BasicMenuItemUI$Handler.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$000(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.awt.EventQueue$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.awt.EventQueue$2.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)81240560
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

显然您的应用程序没有足够的内存来完成操作。 所以你需要为你的虚拟机指定内存标志。 您可以尝试以下操作：

 java -Xms256m -Xmx512m YourApp

在哪里：

• 您的程序在启动时分配的 Xms 最小内存（在示例中为 256 MB）
• 如果需要更多 Xmx 由您的程序分配的最大内存（在示例中为 512 MB）

Answer 2

可能发生的事情之一是在 Java 中， java.lang.String 得到特殊处理。 字符串是不可变的，因此 JVM 将每个 String 对象放在一个池中。这个池的作用是用作一种“缓存”，如果您创建多个具有实际“文本”的 String 实例值相同，将从池中重用相同的实例。 通过这种方式，创建似乎是大量内部具有相同文本的 String 对象实例实际上将恢复到内存中只有很少的实际 String 实例。 另一方面，如果您使用相同的文本来初始化多个 StringBuilder 实例，这些实例实际上将是单独的实例（包含相同的文本），从而占用更多内存。

另一方面，连接字符串（例如String c = "a"+"b"; ）实际上会创建更多的对象实例，如果您使用 StribgBuilder（例如new StringBuilder("a").append("b"); )。