Jackson 触发的String.intern() bug, 导致内存持续增加，JVM-Java内存泄漏

我在本地用Jackson可以复现这个问题了。

import java.io.IOException;
import java.util.Map;
import java.util.Random;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.ObjectMapper;
public class Test {
  public static void main(String[] args) throws IOException {
//    JsonFactory factory = new JsonFactory().disable(JsonFactory.Feature.INTERN_FIELD_NAMES);
//    ObjectMapper om = new ObjectMapper(factory);
    ObjectMapper om = new ObjectMapper(); 

    Random random = new Random();
    while (true) {
      System.out.println("Press any key to continue");
      System.in.read();
      int key = random.nextInt();
      System.out.println("Generated key: " + key);
      Map<Integer, Boolean> desMap =
          om.readValue(String.format("{\"%s\":\"true\"}", key), new TypeReference<Map<Integer, Boolean>>() {});
      System.out.println("Read map: " + desMap);
    }
  }
}

这是我复现的代码，我每次产生一个随机的integer作为map的key，然后用objectMapper反序列化。然后我运行我的另外一个PrintStringTable的类，可以看到每次产生的Integer都会进入Constant Pool中
如果我把构造ObjectMapper的代码改成我注释掉的代码的话，不管产生多少随机Integer key，都不会进入Constant Pool
PrintStringTable类如下

import sun.jvm.hotspot.memory.StringTable;
import sun.jvm.hotspot.memory.SystemDictionary;
import sun.jvm.hotspot.oops.Instance;
import sun.jvm.hotspot.oops.InstanceKlass;
import sun.jvm.hotspot.oops.OopField;
import sun.jvm.hotspot.oops.TypeArray;
import sun.jvm.hotspot.runtime.VM;
import sun.jvm.hotspot.tools.Tool;
public class PrintStringTable extends Tool {
    public PrintStringTable() {
    }
    public static void main(String args[]) throws Exception {
        if (args.length == 0 || args.length > 1) {
            System.err.println("Usage: java PrintStringTable <PID of the JVM whose string table you want to print>");
            System.exit(1);
        }
        PrintStringTable pst = new PrintStringTable();
        pst.execute(args);
        pst.stop();
    }
    @Override
    public void run() {
        StringTable table = VM.getVM().getStringTable();
        table.stringsDo(new StringPrinter());
    }
    class StringPrinter implements StringTable.StringVisitor {
        private final OopField stringValueField;
        public StringPrinter() {
            InstanceKlass strKlass = SystemDictionary.getStringKlass();
            stringValueField = (OopField) strKlass.findField("value", "[C");
        }
        @Override
        public void visit(Instance instance) {
            TypeArray charArray = ((TypeArray) stringValueField.getValue(instance));
            StringBuilder sb = new StringBuilder();
            for (long i = 0; i < charArray.getLength(); i++) {
                sb.append(charArray.getCharAt(i));
            }
            System.out.println("Address: " + instance.getHandle() + " Content: " + sb.toString());
        }
    }
}

需要用/{jdk_HOME}/lib/sa-jdi.jar进行编译和运行，运行参数是需要attach的pid

修改要点

protected JsonFactory factory = new JsonFactory().disable(JsonFactory.Feature.INTERN_FIELD_NAMES);
protected ObjectMapper mapper = new ObjectMapper(factory).setTimeZone(TimeZone.getDefault());

参考Oracle Java 官方文档

https://docs.oracle.com/javase/8/docs/technotes/guides/vm/nmt-8.html

https://docs.oracle.com/javase/8/docs/technotes/guides/troubleshoot/tooldescr007.html （Native Memory Tracking）