Java 16 provides production ready ZGC garbage collection.

For example here is a sample code that is going to run out of memory with a regular JRE integration, I compared the code run with Java 8 and Java 16. There is an option to log the GC cycles with a VM option, but i felt it was too overwhelming for me to understand, so I took a simpler stats information.

package me.sathish;

import java.time.Duration;
import java.time.LocalDateTime;
import java.util.ArrayList;
import java.util.List;

public class MemorySample {
    public static void main(String[] args) {
        LocalDateTime startTime = LocalDateTime.now();
        System.out.println("Starting time--" + startTime);
        getMemoryStats();
        List<Integer> someList = new ArrayList<>();
        List<Integer> someList1 = new ArrayList<>();
        try {
            for (int i = 0; i < 100000000; i++) {
                someList.add(i);
                someList1.add(i);
            }
        } finally {
            Duration duration = Duration.between(LocalDateTime.now(), startTime);
            getMemoryStats();
            System.out.println("The time diff is --" + duration.getSeconds());
        }
    }

    /**
     * Code barrowed from 
     * https://www.viralpatel.net/getting-jvm-heap-size-used-memory-total-memory-using-java-runtime/
     */
    private static void getMemoryStats() {
        Runtime runtime = Runtime.getRuntime();
        int mb = 1024 * 1024;
        System.out.println("##### Heap utilization statistics [MB] #####");
        //Print free memory
        System.out.println("Used Memory:"
                + (runtime.totalMemory() - runtime.freeMemory()) / mb);
        System.out.println("Free Memory:"
                + runtime.freeMemory() / mb);
        System.out.println("Total Memory:" + runtime.totalMemory() / mb);
        System.out.println("Max Memory:" + runtime.maxMemory() / mb);
    }
}

Now with JAVA 8 the increase the heap VM options to –Xmx4096m– took a total of 18 seconds to complete the above program

##### Start Heap utilization statistics [MB] #####
Used Memory:2
Free Memory:189
Total Memory:192
Max Memory:4096


##### End Heap utilization statistics [MB] #####
Used Memory:3857
Free Memory:238
Total Memory:4096
Max Memory:4096
The time diff is ---18

Enter new JAVA 16 world., with VM options -Xmx4096m -XX:+UseZGC

Total Memory:192
Max Memory:4096
##### Heap utilization statistics [MB] #####
Used Memory:3492
Free Memory:604
Total Memory:4096
Max Memory:4096
The time diff is ---29
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
	at java.base/java.util.Arrays.copyOf(Arrays.java:3511)
	at java.base/java.util.Arrays.copyOf(Arrays.java:3480)
	at java.base/java.util.ArrayList.grow(ArrayList.java:237)
	at java.base/java.util.ArrayList.grow(ArrayList.java:244)
	at java.base/java.util.ArrayList.add(ArrayList.java:454)
	at java.base/java.util.ArrayList.add(ArrayList.java:467)

Another set of options that JAVA 16 gives., new VM options for this run was

-XX:+UseZGC -XX:ZUncommitDelay=10 -XX:MaxHeapSize=10000000024,

A slick 10 seconds to complete everything

##### Start Heap utilization statistics [MB] #####
Used Memory:8
Free Memory:184
Total Memory:192
Max Memory:9538

##### End Heap utilization statistics [MB] #####
Used Memory:7548
Free Memory:0
Total Memory:7548
Max Memory:9538
The time diff is ---10

With JAVA 16 the uncommitDelay can be reduced, so with the following VM options

-XX:+UseZGC -Xmx9538m -XX:ZUncommitDelay=1, the code finished with a 44 second runtime.

Take note of the free memory.

##### Start Heap utilization statistics [MB] #####
Used Memory:8
Free Memory:184
Total Memory:192
Max Memory:9538
##### End Heap utilization statistics [MB] #####
Used Memory:6938
Free Memory:0
Total Memory:6938
Max Memory:9538
The time diff is ---44

So tried one other option with the a cool concurrent GC thread option so the new VM options are

XX:MaxHeapSize=10000000024 -XX:+UseParallelGC -XX:ConcGCThreads=4 -XX:ZUncommitDelay=1

The output for the VM options. The code took the time to complete, but the amount of free memory was around full 1038MB

##### Start Heap utilization statistics [MB] #####
Used Memory:4
Free Memory:179
Total Memory:184
Max Memory:8478
##### End Heap utilization statistics [MB] #####
Used Memory:3862
Free Memory:1038
Total Memory:4901
Max Memory:8478
The time diff is ---115

finally, one last VM options and the output, with a balance of memory usage

-XX:+UseZGC -XX:MaxHeapSize=5126M -XX:ZUncommitDelay=1

##### Start Heap utilization statistics [MB] #####
Used Memory:8
Free Memory:184
Total Memory:192
Max Memory:5126
##### End Heap utilization statistics [MB] #####
Used Memory:4674
Free Memory:452
Total Memory:5126
Max Memory:5126
The time diff is ---52

So nice production ready options with JAVA 16 to work with the new ZGC GC model.

Finally always a great watch.,

There are different ways to get a custom error message page in spring boot. The following solution worked for my web project. Here is the overview of the structure.

Pic

To start with, if there is 404 error, then we want a custom error page showing up instead of the spring boot’s default page.
The first thing we are going handle is to suppress the boot framework’s error page. For this, we will go to the application properties and add the following line

server.error.whitelabel.enabled=false

As we are done with that, now let us implement the ErrorController interface. The thing to keep in mind is, we have the LOG entry that says what happened to the code base as we reached here. Here is the sample code.

@Controller
public class ITContractErrorController implements ErrorController     {
    public static final Logger LOG = LoggerFactory.getLogger(ITContractErrorController.class);
    @Autowired
    ErrorAttributes errorAttributes;
    @GetMapping({"${server.error.path:${error.path:/error}}"})
    public String handleError() {
        LOG.error("Sever error occured");
        return "/error/error.html";
    }
@Override
public String getErrorPath() {
    return "error";
    }
}

One other way that we can add the custom error message is using the Spring 2.x’s ConfigurableServletWebServerFactory implementation. We add this to the main method of the web module. Here is the sample code for this entry.

@SpringBootApplication
public class SkminfycontractorWebmoduleApplication {
    @Bean
    public ConfigurableServletWebServerFactory         containerCustomizer(){
        TomcatServletWebServerFactory factory = new     TomcatServletWebServerFactory();
        factory.addErrorPages(new ErrorPage(HttpStatus.NOT_FOUND,     "/error/error.html"));
        return factory;
    }
    public static void main(String[] args) {
        SpringApplication.run(SkminfycontractorWebmoduleApplication.class, args);
    }
}

One thing to remember is, when we implement the override with ConfigurableServeletFactory then Override that is ErrorController is gone.

There is a lot of best practice information laid out in spring documentation and other places. But none worked for my setup. I will update this entry if I find a more interesting solution.