Structured tag api (#895)

planetiler-core/pom.xml

@@ -119,6 +119,11 @@
       <artifactId>jackson-dataformat-csv</artifactId>
       <version>${jackson.version}</version>
     </dependency>
+    <dependency>
+      <groupId>com.fasterxml.jackson.datatype</groupId>
+      <artifactId>jackson-datatype-jsr310</artifactId>
+      <version>${jackson.version}</version>
+    </dependency>
     <dependency>
       <groupId>io.prometheus</groupId>
       <artifactId>simpleclient</artifactId>

planetiler-core/src/main/java/com/onthegomap/planetiler/reader/JsonConversion.java

@@ -0,0 +1,46 @@
+package com.onthegomap.planetiler.reader;
+
+import com.fasterxml.jackson.core.JsonProcessingException;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
+import java.io.UncheckedIOException;
+
+/**
+ * Utilities for converting between JSON strings and java objects using Jackson utilities.
+ * <p>
+ * {@link ObjectMapper} are expensive to construct, but not thread safe, so this class reuses the same object mapper
+ * within each thread but does not share between threads.
+ */
+class JsonConversion {
+  private JsonConversion() {}
+
+  @SuppressWarnings("java:S5164") // ignore not calling remove() on mappers since number of threads is limited
+  private static final ThreadLocal<ObjectMapper> MAPPERS = ThreadLocal.withInitial(() -> JsonMapper.builder()
+    .addModule(
+      new JavaTimeModule().addSerializer(Struct.class, new StructSerializer())
+    )
+    .configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false)
+    .build());
+
+  public static String writeValueAsString(Object o) {
+    try {
+      return o == null ? null : MAPPERS.get().writeValueAsString(o);
+    } catch (JsonProcessingException e) {
+      throw new UncheckedIOException(e);
+    }
+  }
+
+  public static <T> T convertValue(Object o, Class<T> clazz) {
+    return o == null ? null : MAPPERS.get().convertValue(o, clazz);
+  }
+
+  public static <T> T readValue(String string, Class<T> clazz) {
+    try {
+      return string == null ? null : MAPPERS.get().readValue(string, clazz);
+    } catch (JsonProcessingException e) {
+      return null;
+    }
+  }
+}

planetiler-core/src/main/java/com/onthegomap/planetiler/reader/SourceFeature.java

@@ -77,15 +77,6 @@ public boolean hasTag(String key) {
   }
 
 
-  @Override
-  public Object getTag(String key, Object defaultValue) {
-    Object val = tags.get(key);
-    if (val == null) {
-      return defaultValue;
-    }
-    return val;
-  }
-
   @Override
   public Map<String, Object> tags() {
     return tags;