我想将大型 Map
(1.785.530 条目)的内容格式化并写入文本文件。在处理了大约 85% 的条目后,它变得非常慢,然后我得到一个 OutOfMemoryException
。
同样的错误发生,即使我:
- 在我的
FileWriter
上定期调用flush()
或close()
- 使用
BufferedWriter
- 在写入文件之前将每一行写入
StringBuffer
这是我的代码:
private static final TreeMap<Date, Integer> accessesPerSecondMap = new
TreeMap<>();
...
private static void writeOutputFile() throws IOException {
FileWriter writer = new FileWriter(FILENAME_OUTPUT);
writer.write("Date");
writer.write(',');
writer.write("Request Count");
writer.write('\n');
for (Date date : accessesPerSecondMap.keySet()) {
// first and last date are not precise so do not write it in the
// file
if (date == accessesPerSecondMap.firstKey()
|| date == accessesPerSecondMap.lastKey()) {
continue;
}
writer.write(String.valueOf(date));
System.out.println("FileMerger wrote: " + String.valueOf(date));
writer.write(',');
writer.write(String.valueOf(accessesPerSecondMap.get(date)));
writer.write('\n');
}
writer.flush();
writer.close();
}
这是抛出的异常:
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
at sun.util.resources.TimeZoneNames.getContents(Unknown Source)
at sun.util.resources.OpenListResourceBundle.loadLookup(Unknown Source)
at sun.util.resources.OpenListResourceBundle.loadLookupTablesIfNecessary(Unknown Source)
at sun.util.resources.OpenListResourceBundle.handleKeySet(Unknown Source)
at java.util.ResourceBundle.containsKey(Unknown Source)
at sun.util.locale.provider.LocaleResources.getTimeZoneNames(Unknown Source)
at sun.util.locale.provider.TimeZoneNameProviderImpl.getDisplayNameArray(Unknown Source)
at sun.util.locale.provider.TimeZoneNameProviderImpl.getDisplayName(Unknown Source)
at sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter.getName(Unknown Source)
at sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter.getObject(Unknown Source)
at sun.util.locale.provider.TimeZoneNameUtility$TimeZoneNameGetter.getObject(Unknown Source)
at sun.util.locale.provider.LocaleServiceProviderPool.getLocalizedObjectImpl(Unknown Source)
at sun.util.locale.provider.LocaleServiceProviderPool.getLocalizedObject(Unknown Source)
at sun.util.locale.provider.TimeZoneNameUtility.retrieveDisplayName(Unknown Source)
at java.util.TimeZone.getDisplayName(Unknown Source)
at java.util.Date.toString(Unknown Source)
at java.lang.String.valueOf(Unknown Source)
at FileMerger.writeOutputFile(FileMerger.java:95)
at FileMerger.main(FileMerger.java:26)
增加堆空间对我有用,但在我看来并不是一个真正令人满意的解决方案。几天后,我将不得不编写两倍大的文件;希望空间也足够他们使用。
我在 Windows 上运行 Java 1.8.0_45。上面的代码是真实的代码,也是唯一运行的代码。出于测试目的,我使用以下代码填充 TreeMap
:
int accesses = 43267;
for (int i = 0; i < 1785530; i++) {
Date date = new Date(i);
accessesPerSecondMap.put(date, accesses);
}
我已将以下内容添加到 for 循环以跟踪内存使用情况:
...
int count = 100000;
for (Date date : accessesPerSecondMap.keySet()) {
if (count == 100000) {
count = 0;
printOutMemoryUsage();
}
count++;
...
private void printOutMemoryUsage() {
Runtime runtime = Runtime.getRuntime();
NumberFormat format = NumberFormat.getInstance();
StringBuilder sb = new StringBuilder();
long maxMemory = runtime.maxMemory();
long allocatedMemory = runtime.totalMemory();
long freeMemory = runtime.freeMemory();
sb.append("free memory: " + format.format(freeMemory / 1024) + " ");
sb.append("allocated memory: " + format.format(allocatedMemory / 1024)
+ " ");
sb.append("max memory: " + format.format(maxMemory / 1024) + " ");
sb.append("total free memory: "
+ format.format((freeMemory + (maxMemory - allocatedMemory)) / 1024)
+ "<br/>");
System.out.println(sb);
}
当我不增加堆空间时,我得到这个输出:
free memory: 28.868 allocated memory: 156.792 max memory: 253.440 total free memory: 125.516
free memory: 89.847 allocated memory: 253.440 max memory: 253.440 total free memory: 89.847
free memory: 87.796 allocated memory: 253.440 max memory: 253.440 total free memory: 87.796
free memory: 89.758 allocated memory: 253.440 max memory: 253.440 total free memory: 89.758
free memory: 32.478 allocated memory: 253.440 max memory: 253.440 total free memory: 32.478
free memory: 35.182 allocated memory: 253.440 max memory: 253.440 total free memory: 35.182
free memory: 37.269 allocated memory: 253.440 max memory: 253.440 total free memory: 37.269
free memory: 45.165 allocated memory: 253.440 max memory: 253.440 total free memory: 45.165
free memory: 42.943 allocated memory: 253.440 max memory: 253.440 total free memory: 42.943
free memory: 32.055 allocated memory: 253.440 max memory: 253.440 total free memory: 32.055
free memory: 13.053 allocated memory: 253.440 max memory: 253.440 total free memory: 13.053
free memory: 14.281 allocated memory: 253.440 max memory: 253.440 total free memory: 14.281
free memory: 12.797 allocated memory: 253.440 max memory: 253.440 total free memory: 12.797
free memory: 1.973 allocated memory: 253.440 max memory: 253.440 total free memory: 1.973
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
随着堆空间的增加 -Xms512m -Xmx1230m
我得到:
free memory: 372.630 allocated memory: 506.816 max memory: 1.217.536 total free memory: 1.083.350
free memory: 329.031 allocated memory: 506.816 max memory: 1.217.536 total free memory: 1.039.751
free memory: 273.121 allocated memory: 506.816 max memory: 1.217.536 total free memory: 983.841
free memory: 333.700 allocated memory: 506.816 max memory: 1.217.536 total free memory: 1.044.420
free memory: 276.392 allocated memory: 506.816 max memory: 1.217.536 total free memory: 987.112
free memory: 220.482 allocated memory: 506.816 max memory: 1.217.536 total free memory: 931.202
free memory: 279.896 allocated memory: 506.816 max memory: 1.217.536 total free memory: 990.616
free memory: 223.986 allocated memory: 506.816 max memory: 1.217.536 total free memory: 934.706
free memory: 284.565 allocated memory: 506.816 max memory: 1.217.536 total free memory: 995.285
free memory: 228.654 allocated memory: 506.816 max memory: 1.217.536 total free memory: 939.374
free memory: 169.949 allocated memory: 506.816 max memory: 1.217.536 total free memory: 880.669
free memory: 230.528 allocated memory: 506.816 max memory: 1.217.536 total free memory: 941.248
free memory: 174.618 allocated memory: 506.816 max memory: 1.217.536 total free memory: 885.338
free memory: 235.197 allocated memory: 506.816 max memory: 1.217.536 total free memory: 945.917
free memory: 179.287 allocated memory: 506.816 max memory: 1.217.536 total free memory: 890.007
free memory: 123.376 allocated memory: 506.816 max memory: 1.217.536 total free memory: 834.096
free memory: 183.956 allocated memory: 506.816 max memory: 1.217.536 total free memory: 894.676
free memory: 128.046 allocated memory: 506.816 max memory: 1.217.536 total free memory: 838.766
FileMerger main method finished
最佳答案
一般有两种方法可以消除这个错误
java.lang.OutOfMemoryError: Java heap space
- 允许 JVM 使用更多内存
使用 -Xmx JVM 参数,您可以设置堆大小。在命令行上使用 java -Xms -Xmx。
- 使用Eclipse Memory Analyzer Eclipse memory analyzer是eclipse基金会的一个工具,用于分析java堆转储。它有助于发现类加载器泄漏和内存泄漏,并有助于最大限度地减少内存消耗。您可以使用 MAT 分析携带数百万对象的堆转储,它还可以帮助您提取内存泄漏的嫌疑。
关于java - FileWriter 内存不足,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/30491253/