Extract JsonWriter for json output

src/main/java/org/asamk/signal/JsonWriter.java

@@ -0,0 +1,37 @@
+package org.asamk.signal;
+
+import com.fasterxml.jackson.annotation.JsonAutoDetect;
+import com.fasterxml.jackson.annotation.PropertyAccessor;
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.OutputStreamWriter;
+import java.nio.charset.StandardCharsets;
+
+public class JsonWriter {
+
+    private final OutputStreamWriter writer;
+    private final ObjectMapper objectMapper;
+
+    public JsonWriter(final OutputStream writer) {
+        this.writer = new OutputStreamWriter(writer, StandardCharsets.UTF_8);
+
+        objectMapper = new ObjectMapper();
+        objectMapper.setVisibility(PropertyAccessor.ALL, JsonAutoDetect.Visibility.ANY);
+        objectMapper.disable(JsonGenerator.Feature.AUTO_CLOSE_TARGET);
+    }
+
+    public void write(final Object object) throws IOException {
+        try {
+            objectMapper.writeValue(writer, object);
+        } catch (JsonProcessingException e) {
+            // Some issue with json serialization, probably caused by a bug
+            throw new AssertionError(e);
+        }
+        writer.write(System.lineSeparator());
+        writer.flush();
+    }
+}