Add passing tests trying to reproduce #4321 (#4322)

src/test/java/com/fasterxml/jackson/databind/util/BufferRecyclersDatabindTest.java

@@ -0,0 +1,118 @@
+package com.fasterxml.jackson.databind.util;
+
+import java.nio.charset.StandardCharsets;
+
+import com.fasterxml.jackson.annotation.JsonPropertyOrder;
+
+import com.fasterxml.jackson.core.*;
+
+import com.fasterxml.jackson.core.util.BufferRecycler;
+import com.fasterxml.jackson.core.util.JsonRecyclerPools;
+import com.fasterxml.jackson.core.util.RecyclerPool;
+
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+
+// For [databind#4321]: basic test
+public class BufferRecyclersDatabindTest
+    extends BaseMapTest
+{
+    @JsonPropertyOrder({ "a", "b" })
+    static class Pojo4321 {
+        public int a;
+        public String b;
+
+        public Pojo4321(int a, String b) {
+            this.a = a;
+            this.b = b;
+        }
+        protected Pojo4321() { }
+    }
+
+    // // Parsers with RecyclerPools:
+
+    public void testParserWithThreadLocalPool() throws Exception {
+        _testParser(JsonRecyclerPools.threadLocalPool());
+    }
+
+    public void testParserWithNopLocalPool() throws Exception {
+        _testParser(JsonRecyclerPools.nonRecyclingPool());
+    }
+
+    public void testParserWithDequeuPool() throws Exception {
+        _testParser(JsonRecyclerPools.newConcurrentDequePool());
+        _testParser(JsonRecyclerPools.sharedConcurrentDequePool());
+    }
+
+    public void testParserWithLockFreePool() throws Exception {
+        _testParser(JsonRecyclerPools.newLockFreePool());
+        _testParser(JsonRecyclerPools.sharedLockFreePool());
+    }
+
+    public void testParserWithBoundedPool() throws Exception {
+        _testParser(JsonRecyclerPools.newBoundedPool(5));
+        _testParser(JsonRecyclerPools.sharedBoundedPool());
+    }
+
+    private void _testParser(RecyclerPool<BufferRecycler> pool) throws Exception
+    {
+        ObjectMapper mapper = JsonMapper.builder(
+                JsonFactory.builder()
+                    .recyclerPool(pool)
+                    .build()).build();
+        final String DOC = "{\"a\":123,\"b\":\"foobar\"}";
+
+        // Let's first test using char-backed parser
+        Pojo4321 value = mapper.readerFor(Pojo4321.class)
+                .readValue(DOC);
+        assertEquals(123, value.a);
+        assertEquals("foobar", value.b);
+
+        // and then byte-backed parser
+        value = mapper.readerFor(Pojo4321.class)
+                .readValue(utf8Bytes(DOC));
+        assertEquals(123, value.a);
+        assertEquals("foobar", value.b);
+    }
+
+    // // Generators with RecyclerPools:
+
+    public void testGeneratorWithThreadLocalPool() throws Exception {
+        _testGenerator(JsonRecyclerPools.threadLocalPool());
+    }
+
+    public void testGeneratorWithNopLocalPool() throws Exception {
+        _testGenerator(JsonRecyclerPools.nonRecyclingPool());
+    }
+
+    public void testGeneratorWithDequeuPool() throws Exception {
+        _testGenerator(JsonRecyclerPools.newConcurrentDequePool());
+        _testGenerator(JsonRecyclerPools.sharedConcurrentDequePool());
+    }
+
+    public void testGeneratorWithLockFreePool() throws Exception {
+        _testGenerator(JsonRecyclerPools.newLockFreePool());
+        _testGenerator(JsonRecyclerPools.sharedLockFreePool());
+    }
+
+    public void testGeneratorWithBoundedPool() throws Exception {
+        _testGenerator(JsonRecyclerPools.newBoundedPool(5));
+        _testGenerator(JsonRecyclerPools.sharedBoundedPool());
+    }
+
+    private void _testGenerator(RecyclerPool<BufferRecycler> pool) throws Exception
+    {
+        ObjectMapper mapper = JsonMapper.builder(
+                JsonFactory.builder()
+                    .recyclerPool(pool)
+                    .build()).build();
+        final String EXP = "{\"a\":-42,\"b\":\"bogus\"}";
+
+        // First write as String
+        assertEquals(EXP, mapper.writeValueAsString(new Pojo4321(-42, "bogus")));
+
+        // and then as bytes
+        assertEquals(EXP, new String(mapper.writeValueAsBytes(new Pojo4321(-42, "bogus")),
+                StandardCharsets.UTF_8));
+    }
+}