[feature]adding fixed gauge meter and updating counter meter with amount

README.md

@@ -438,14 +438,27 @@ we have 3 types of metric : TIMER , COUNTER , GAUGE. you can register your custo
                             "description",
                             tags); 
 ```
-as you see, you should specify your metric with a valid type and a name. additionally, if wanted, you can add description or tags to your registering metric.
+as you see, you should specify your metric with a valid type and a name. additionally, if wanted, you can add description or tags to your registering metric.<br>
+you can also register a gauge meter with specifying its initial value:
+```
+    meterUtil.registerFixedInitGaugeMeter("meterName",
+                            "description",
+                            tags,
+                            initialValue); 
+```
+note that the initialValue is Long and this kind of gauge metric can not be updated by incrementing or decrementing its value.
+
 #### updating metrics
 we have three types of metric that for each one, we provided a proper updating mechanism:
 1. updating COUNTER meter: by updating this type of meter you will increment the value of it.<br>
    example:
 ```
     meterUtil.updateCounterMeter("meterName", tags);
 ```
+and if you want to increment your counter metric by an specified amount (double):
+```
+    meterUtil.updateCounterMeter("meterName", tags, amount);
+```
 - note : you can pass null instead of _tags_ if you did not specify tags for your metric in the first place.
 
 2.updating TIMER meter: by updating the timer meter, you can record your wanted duration in milliseconds.<br>

tosan-httpserver-spring-boot-starter/src/main/java/com/tosan/http/server/starter/metrics/GaugeValue.java

@@ -7,7 +7,7 @@
  * @since 2/13/2024
  */
 public class GaugeValue {
-    private static final AtomicInteger value = new AtomicInteger(0);
+    private final AtomicInteger value = new AtomicInteger(0);
 
     public void increment() {
         value.incrementAndGet();

tosan-httpserver-spring-boot-starter/src/main/java/com/tosan/http/server/starter/metrics/util/MeterUtil.java

@@ -38,6 +38,16 @@ public Meter registerMeter(MeterType meterType, String meterName, String descrip
         return meters.get(key);
     }
 
+    public Meter registerFixedInitGaugeMeter(String meterName, String description, Tags tags, Long value) {
+        String key = createKey(meterName, tags);
+        if (!meters.containsKey(key)) {
+            synchronized (meters) {
+                meters.computeIfAbsent(key, ignore -> registerFixedGaugeMeter(meterName, description, tags, value));
+            }
+        }
+        return meters.get(key);
+    }
+
     public void updateTimerMeter(String metricName, Tags tags, long duration) {
         String key = createKey(metricName, tags);
         if (!meters.isEmpty() && meters.get(key) != null) {
@@ -54,12 +64,19 @@ public void updateCounterMeter(String metricName, Tags tags) {
         }
     }
 
+    public void updateCounterMeterByFixedAmount(String metricName, Tags tags, double amount) {
+        String key = createKey(metricName, tags);
+        if (!meters.isEmpty() && meters.get(key) != null) {
+            Meter meter = meters.get(key);
+            ((Counter) meter).increment(amount);
+        }
+    }
+
     public void updateGaugeMeterByIncrementing(String metricName, Tags tags) {
         String key = createKey(metricName, tags);
         if (!meters.isEmpty() && gaugeMeters.get(key) != null) {
             GaugeValue gaugeValue = gaugeMeters.get(createKey(metricName, tags));
             gaugeValue.increment();
-            gaugeMeters.put(createKey(metricName, tags), gaugeValue);
         }
     }
 
@@ -68,7 +85,6 @@ public void updateGaugeMeterByDecrementing(String metricName, Tags tags) {
         if (!gaugeMeters.isEmpty() && gaugeMeters.get(key) != null) {
             GaugeValue gaugeValue = gaugeMeters.get(createKey(metricName, tags));
             gaugeValue.decrement();
-            gaugeMeters.put(createKey(metricName, tags), gaugeValue);
         }
     }
 
@@ -129,20 +145,35 @@ private Timer registerTimerMeter(String metricName, String description, Tags tag
         }
     }
 
-    private Gauge registerGaugeMeter(String metricName, String desctiption, Tags tags) {
+    private Gauge registerGaugeMeter(String metricName, String description, Tags tags) {
         GaugeValue gaugeValue = new GaugeValue();
         Gauge gauge;
         if (tags == null) {
             gauge = Gauge.builder(metricName, gaugeValue::getValue)
-                    .description(desctiption)
+                    .description(description)
                     .register(meterRegistry);
         } else {
             gauge = Gauge.builder(metricName, gaugeValue::getValue)
-                    .description(desctiption)
+                    .description(description)
                     .tags(tags)
                     .register(meterRegistry);
         }
         gaugeMeters.put(createKey(metricName, tags), gaugeValue);
         return gauge;
     }
+
+    private Gauge registerFixedGaugeMeter(String metricName, String description, Tags tags, Long value) {
+        Gauge gauge;
+        if (tags == null) {
+            gauge = Gauge.builder(metricName, value::longValue)
+                    .description(description)
+                    .register(meterRegistry);
+        } else {
+            gauge = Gauge.builder(metricName, value::longValue)
+                    .description(description)
+                    .tags(tags)
+                    .register(meterRegistry);
+        }
+        return gauge;
+    }
 }