StringBuilder 导致堆内存溢出

StringBuilder 导致堆内存溢出

原始问题描述:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at java.util.Arrays.copyOf(Arrays.java:3332)
	at java.lang.AbstractStringBuilder.ensureCapacityInternal(AbstractStringBuilder.java:124)
	at java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:448)
	at java.lang.StringBuilder.append(StringBuilder.java:136)
	at testpkg.Main.decDfs(Main.java:230)


定位到问题点:

/**
 * For positive values of {@code minimumCapacity}, this method
 * behaves like {@code ensureCapacity}, however it is never
 * synchronized.
 * If {@code minimumCapacity} is non positive due to numeric
 * overflow, this method throws {@code OutOfMemoryError}.
 */
private void ensureCapacityInternal(int minimumCapacity) {
    // overflow-conscious code
    if (minimumCapacity - value.length > 0) {
        value = Arrays.copyOf(value,
                              newCapacity(minimumCapacity));
    }
}

问题的原因在于无脑 append 的时候,扩充内存使得 StringBuilder 的长度超过了上限触发OOM,查看后发现 StringBuilder 实际能使用的大小和 JVM 。

解决方法:

  • 调大JVM参数,因为StringBuilder有时候没有到达上限,由于JVM堆空间太小,也会触发OOM
  • 重新计算最大所需空间,增加 StringBuilder 数量,提前分散放置字符串
  • 提前序列化部分结果,但是效率很低
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