Jackson triggered the String. intern () bug, resulting in a continuous increase in memory, JVM-Java Memory leakage,

Jackson triggered the String. intern () bug, resulting in a continuous increase in memory, JVM-Java Memory leakage,

I can use Jackson locally to reproduce this problem.

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);     }   } } 

This is the code I reproduced. Every time I generate a random integer as the map key, I use objectMapper for deserialization. Then I run another PrintStringTable class, and we can see that each Integer generated enters the Constant Pool.
If I change the code for constructing ObjectMapper to the code I commented out, no matter how many random Integer keys are generated, they will not enter the Constant Pool.
The PrintStringTable class is as follows:

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());         }     } } 

 

The/{jdk_HOME}/lib/sa-jdi.jar needs to be compiled and run. The running parameter is the pid of attach.

 

Key points for Modification

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

 

 

See Oracle Java official documentation

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)