Jackson 觸發的String.intern() bug, 導致記憶體持續增加，JVM-Java記憶體泄漏

我在本地用Jackson可以復現這個問題了。

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); 
    } 
  } 
} 

這是我復現的代碼，我每次產生一個隨機的integer作為map的key，然後用objectMapper反序列化。然後我運行我的另外一個PrintStringTable的類，可以看到每次產生的Integer都會進入Constant Pool中
如果我把構造ObjectMapper的代碼改成我註釋掉的代碼的話，不管產生多少隨機Integer key，都不會進入Constant Pool
PrintStringTable類如下

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進行編譯和運行，運行參數是需要attach的pid

 修改要點

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

參考Oracle Java 官方文檔

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）