Basic golang web server.

.gitignore

@@ -3,3 +3,5 @@ output-vagrant
 .git
 .vagrant
 .secret
+*.iml
+.idea

2024/07/golang_demo1/go.mod

@@ -0,0 +1,3 @@
+module golang_demo1
+
+go 1.22

2024/07/golang_demo1/main.go

@@ -0,0 +1,97 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"net/http"
+	"time"
+)
+
+type PersonRequest struct {
+	Name string
+	Age  int
+}
+
+type PersonResponse struct {
+	Greeting string
+	Errors   string
+}
+
+type StatusResponse struct {
+	StartDateTime string
+	UpTime        string
+	Status        string
+}
+
+var startTime = time.Now()
+
+func main() {
+	portPtr := flag.Int("port", 8080, "port for webserver")
+	flag.Parse()
+	port := *portPtr
+
+	fmt.Printf("Server is listening on port: %d", port)
+
+	server := http.NewServeMux()
+	server.HandleFunc("/status", statusHandler)
+	server.HandleFunc("/greeting", greetingHandler)
+	err := http.ListenAndServe(fmt.Sprintf("localhost:%d", port), server)
+
+	if err != nil {
+		fmt.Println("Error:", err)
+		return
+	}
+}
+
+func greetingHandler(writer http.ResponseWriter, request *http.Request) {
+	decoder := json.NewDecoder(request.Body)
+	decoder.DisallowUnknownFields()
+	var p = PersonRequest{}
+	errDecode := decoder.Decode(&p)
+	if errDecode != nil {
+		println("Error: ", errDecode)
+		writer.WriteHeader(400)
+		_, _ = writer.Write([]byte("Bad request data"))
+		return
+	}
+
+	r := PersonResponse{
+		Greeting: fmt.Sprintf("Hey %s. Your age is %d", p.Name, p.Age),
+		Errors:   "",
+	}
+
+	writer.Header().Add("Content-Type", "application/json")
+	encoder := produceEncoder(writer)
+	errEncode := encoder.Encode(&r)
+	if errEncode != nil {
+		writer.WriteHeader(500)
+		println("Error: ", errEncode)
+		return
+	}
+	writer.WriteHeader(200)
+}
+
+func produceEncoder(writer http.ResponseWriter) *json.Encoder {
+	encoder := json.NewEncoder(writer)
+	return encoder
+}
+
+func statusHandler(writer http.ResponseWriter, _ *http.Request) {
+	upTime := time.Now().Unix() - startTime.Unix()
+	status := StatusResponse{
+		Status:        "Ok",
+		StartDateTime: startTime.Format("2006-01-02 15:04:05.000-0700"),
+		UpTime:        fmt.Sprintf("%d", upTime),
+	}
+
+	writer.Header().Add("Content-Type", "application/json")
+	encoder := produceEncoder(writer)
+	errEncode := encoder.Encode(&status)
+	if errEncode != nil {
+		writer.WriteHeader(500)
+		println("Error: ", errEncode)
+		return
+	}
+	writer.WriteHeader(200)
+}

2024/07/spring_demo1/src/main/java/ch/polgrabia/demos/spring_demo1/utils/ListsProgram.java

@@ -0,0 +1,72 @@
+package ch.polgrabia.demos.spring_demo1.utils;
+
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.List;
+
+public class ListsProgram {
+
+    public static class OneDirListItemIteratorImpl<T> implements Iterator<T> {
+
+        private OneDirListItem<T> item;
+
+        public OneDirListItemIteratorImpl(OneDirListItem<T> item) {
+            this.item = item;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return item != null;
+        }
+
+        @Override
+        public T next() {
+            OneDirListItem<T> curr = item;
+            item = item.next;
+            return curr.val;
+        }
+    }
+
+    public static class OneDirListItem<T> implements Iterable<T> {
+        public T val;
+        public OneDirListItem<T> next;
+
+        @Override
+        public Iterator<T> iterator() {
+            return new OneDirListItemIteratorImpl<>(this);
+        }
+    }
+
+    public static <T> OneDirListItem<T> makeOneDirList(List<T> items) {
+        OneDirListItem<T> curr = new OneDirListItem<>();
+        OneDirListItem<T> start = curr;
+        OneDirListItem<T> prev = null;
+        for (T val : items) {
+            curr.val = val;
+            curr.next = new OneDirListItem<T>();
+            prev = curr;
+            curr = curr.next;
+        }
+
+        if (prev != null) {
+            prev.next = null;
+        }
+
+        return start;
+    }
+
+    public static void main(String[] args) {
+        int lastXNr = 5;
+        var l = makeOneDirList(Arrays.asList(10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0));
+        var lastXItems = new LinkedList<Integer>();
+        for (var el : l) {
+            lastXItems.addLast(el);
+            if (lastXItems.size() > lastXNr) {
+                lastXItems.removeFirst();
+            }
+        }
+        Integer first = lastXItems.getFirst();
+        System.out.printf("The last %d element is %d", lastXNr, first);
+    }
+}

2024/07/spring_demo1/src/main/resources/application.properties

@@ -3,4 +3,4 @@ spring.jpa.properties.hibernate.dialect = org.hibernate.dialect.PostgreSQLDialec
 spring.datasource.url=jdbc:postgresql://localhost:5432/app
 spring.datasource.username=postgres
 spring.datasource.password=secret
-spring.jpa.hibernate.ddl-auto=update
+spring.jpa.hibernate.ddl-auto=validate