【案例一】验证CSVParser和RandomAccessFile的内存表现

借助RandomAccessFile和apache.commons.csv包分别解析CSV

CSVParser

首先设置JVM内存为32M，生成CSV文件超过内存

-Xms32m -Xmx32m

public class MyTest {
    public static void main(String[] args) throws IOException, SQLException {
        System.gc();
        createCsv();
        readCsv();
    }
    public static void createCsv() throws IOException {
        if (Files.exists(new File("C:\\Users\\g30038553\\Desktop\\temp\\话单jilu\\test.csv").toPath())) {
            return;
        }
        String s = "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
        FileWriter fw = new FileWriter("C:\\Users\\my\\Desktop\test.csv", true);
        for (int i = 0; i < 100000; i++) {
            fw.write(s);
            fw.write('\n');
            fw.flush();
        }
    }
    public static void readCsv() throws IOException {
        MemoryMXBean memoryMXBean = ManagementFactory.getMemoryMXBean();
        memoryMXBean.setVerbose(true);
        MemoryUsage heapMemoryUsage = memoryMXBean.getHeapMemoryUsage();
        MemoryUsage nonHeapMemoryUsage = memoryMXBean.getNonHeapMemoryUsage();
        long heapMemoryUsaged;
        long nonHeapMemoryUsaged;
        heapMemoryUsaged = heapMemoryUsage.getUsed();
        System.out.println("Heap Memory Usage - init: " + heapMemoryUsaged);
        nonHeapMemoryUsaged = nonHeapMemoryUsage.getUsed();
        System.out.println("nonHeap Memory Usage - init: " + nonHeapMemoryUsaged);

        File file = new File("C:\\Users\\my\\Desktop\test.csv");
        heapMemoryUsage = memoryMXBean.getHeapMemoryUsage();
        heapMemoryUsaged = heapMemoryUsage.getUsed();
        System.out.println("Heap Memory Usage - newFile: " + heapMemoryUsaged);
        nonHeapMemoryUsage = memoryMXBean.getNonHeapMemoryUsage();
        nonHeapMemoryUsaged = nonHeapMemoryUsage.getUsed();
        System.out.println("nonHeap Memory Usage - newFile: " + nonHeapMemoryUsaged);

        CSVFormat defaultFormat = CSVFormat.DEFAULT;
        heapMemoryUsage = memoryMXBean.getHeapMemoryUsage();
        heapMemoryUsaged = heapMemoryUsage.getUsed();
        System.out.println("Heap Memory Usage - newFormat: " + heapMemoryUsaged);
        nonHeapMemoryUsage = memoryMXBean.getNonHeapMemoryUsage();
        nonHeapMemoryUsaged = nonHeapMemoryUsage.getUsed();
        System.out.println("nonHeap Memory Usage - newFormat: " + nonHeapMemoryUsaged);

        CSVParser parse = CSVParser.parse(file, Charset.defaultCharset(), defaultFormat);
        heapMemoryUsage = memoryMXBean.getHeapMemoryUsage();
        heapMemoryUsaged = heapMemoryUsage.getUsed();
        System.out.println("Heap Memory Usage - newParser: " + heapMemoryUsaged);
        nonHeapMemoryUsage = memoryMXBean.getNonHeapMemoryUsage();
        nonHeapMemoryUsaged = nonHeapMemoryUsage.getUsed();
        System.out.println("nonHeap Memory Usage - newParser: " + nonHeapMemoryUsaged);

        List<CSVRecord> records = parse.getRecords();
        heapMemoryUsage = memoryMXBean.getHeapMemoryUsage();
        heapMemoryUsaged = heapMemoryUsage.getUsed();
        System.out.println("Heap Memory Usage - getRecords: " + heapMemoryUsaged);
        nonHeapMemoryUsage = memoryMXBean.getNonHeapMemoryUsage();
        nonHeapMemoryUsaged = nonHeapMemoryUsage.getUsed();
        System.out.println("nonHeap Memory Usage - getRecords: " + nonHeapMemoryUsaged);
        System.out.println(records);
    }
}

CSVParser解析结果显示：

Heap Memory Usage - init: 16790296
nonHeap Memory Usage - init: 6021568
Heap Memory Usage - newFile: 16790296
nonHeap Memory Usage - newFile: 6149160
Heap Memory Usage - newFormat: 16790296
nonHeap Memory Usage - newFormat: 6294384
Heap Memory Usage - newParser: 17838872
nonHeap Memory Usage - newParser: 6392208
……
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
……

堆内存结果显示，构造CSVParser的过程中，堆外内存持续增长，堆内存增长不明显，但最终getRecords时堆内存抛出OOM异常

将重复写字符串的次数调整到5000，再次执行

Heap Memory Usage - init: 16802896
nonHeap Memory Usage - init: 6013848
Heap Memory Usage - newFile: 16802896
nonHeap Memory Usage - newFile: 6133896
Heap Memory Usage - newFormat: 16802896
nonHeap Memory Usage - newFormat: 6288328
Heap Memory Usage - newParser: 17851472
nonHeap Memory Usage - newParser: 6383848

可见在getRecords阶段是堆内存增长的来源