Support for canonical JSON output in Jackson 2.16

src/test/java/com/fasterxml/jackson/databind/ser/CanonicalBigDecimalSerializer.java

@@ -0,0 +1,76 @@
+package com.fasterxml.jackson.databind.ser;
+
+import java.io.IOException;
+import java.math.BigDecimal;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.databind.SerializerProvider;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class CanonicalBigDecimalSerializer extends StdSerializer<BigDecimal>
+        implements ValueToString<BigDecimal> {
+    private static final long serialVersionUID = 1L;
+
+    public static final CanonicalBigDecimalSerializer INSTANCE = new CanonicalBigDecimalSerializer();
+
+    public static final CanonicalNumberSerializerProvider PROVIDER = new CanonicalNumberSerializerProvider() {
+        @Override
+        public StdSerializer<BigDecimal> getNumberSerializer() {
+            return INSTANCE;
+        }
+
+        @Override
+        public ValueToString<BigDecimal> getValueToString() {
+            return INSTANCE;
+        }
+    };
+
+    protected CanonicalBigDecimalSerializer() {
+        super(BigDecimal.class);
+    }
+
+    @Override
+    public void serialize(BigDecimal value, JsonGenerator gen, SerializerProvider provider)
+            throws IOException {
+        CanonicalNumberGenerator.verifyBigDecimalRange(value, provider);
+
+        String output = convert(value);
+        gen.writeNumber(output);
+    }
+
+    @Override
+    public String convert(BigDecimal value) {
+        // TODO Convert to exponential form if necessary
+        BigDecimal stripped = value.stripTrailingZeros();
+        int scale = stripped.scale();
+        String text = stripped.toPlainString();
+        if (scale == 0) {
+            return text;
+        }
+
+        int pos = text.indexOf('.');
+        int exp;
+        if (pos >= 0) {
+            exp = pos - 1;
+
+            if (exp == 0) {
+                return text;
+            }
+
+            text = text.substring(0, pos) + text.substring(pos + 1);
+        } else {
+            exp = -scale;
+            int end = text.length();
+            while (end > 0 && text.charAt(end - 1) == '0') {
+                end --;
+            }
+            text = text.substring(0, end);
+        }
+
+        if (text.length() == 1) {
+            return text + 'E' + exp;
+        }
+
+        return text.substring(0, 1) + '.' + text.substring(1) + 'E' + exp;
+    }
+}

src/test/java/com/fasterxml/jackson/databind/ser/CanonicalBigDecimalSerializerTest.java

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+package com.fasterxml.jackson.databind.ser;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.math.BigDecimal;
+
+import org.junit.jupiter.api.Test;
+
+public class CanonicalBigDecimalSerializerTest {
+
+    @Test
+    void testCanonicalDecimalHandling_1() throws Exception {
+        assertSerialized("1", new BigDecimal("1"));
+    }
+
+    @Test
+    void testCanonicalDecimalHandling_1_000() throws Exception {
+        assertSerialized("1", new BigDecimal("1.000"));
+    }
+
+    @Test
+    void testCanonicalDecimalHandling_10_1000() throws Exception {
+        assertSerialized("1.01E1", new BigDecimal("10.1000"));
+    }
+
+    @Test
+    void testCanonicalDecimalHandling_1000() throws Exception {
+        assertSerialized("1E3", new BigDecimal("1000"));
+    }
+
+    @Test
+    void testCanonicalDecimalHandling_0_00000000010() throws Exception {
+        assertSerialized("0.0000000001", new BigDecimal("0.00000000010"));
+    }
+
+    @Test
+    void testCanonicalDecimalHandling_1000_00010() throws Exception {
+        assertSerialized("1.0000001E3", new BigDecimal("1000.00010"));
+    }
+
+    @Test
+    void testCanonicalHugeDecimalHandling() throws Exception {
+        BigDecimal actual = new BigDecimal("123456789123456789123456789123456789.123456789123456789123456789123456789123456789000");
+        assertSerialized("1.23456789123456789123456789123456789123456789123456789123456789123456789123456789E35", actual);
+    }
+
+    private void assertSerialized(String expected, BigDecimal actual) {
+        CanonicalBigDecimalSerializer serializer = new CanonicalBigDecimalSerializer();
+        assertEquals(expected, serializer.convert(actual));
+    }
+
+}

src/test/java/com/fasterxml/jackson/databind/ser/CanonicalJsonFactory.java

@@ -0,0 +1,30 @@
+package com.fasterxml.jackson.databind.ser;
+
+import java.io.IOException;
+import java.io.Writer;
+import java.math.BigDecimal;
+
+import com.fasterxml.jackson.core.JsonGenerator;
+import com.fasterxml.jackson.core.io.IOContext;
+import com.fasterxml.jackson.core.JsonFactory;
+
+/**
+ * TODO Fix double numbers. This feels like a very heavy solution plus I can't
+ * use the JsonFactory.builder().
+ */
+public class CanonicalJsonFactory extends JsonFactory {
+    private static final long serialVersionUID = 1L;
+
+    private ValueToString<BigDecimal> _serializer;
+
+    public CanonicalJsonFactory(ValueToString<BigDecimal> serializer) {
+        this._serializer = serializer;
+    }
+
+    @Override
+    protected JsonGenerator _createGenerator(Writer out, IOContext ioCtxt)
+            throws IOException {
+        JsonGenerator delegate = super._createGenerator(out, ioCtxt);
+        return new CanonicalNumberGenerator(delegate, _serializer);
+    }
+}

src/test/java/com/fasterxml/jackson/databind/ser/CanonicalJsonMapper.java

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+package com.fasterxml.jackson.databind.ser;
+
+import com.fasterxml.jackson.core.StreamWriteFeature;
+import com.fasterxml.jackson.databind.MapperFeature;
+import com.fasterxml.jackson.databind.SerializationFeature;
+import com.fasterxml.jackson.databind.json.JsonMapper;
+
+public class CanonicalJsonMapper { // TODO It would be great if we could extend JsonMapper but the return type of builder() is incompatible
+
+    public static class Builder { // TODO Can't extend MapperBuilder<JsonMapper, Builder> because that needs JsonFactory as ctor arg and we only have this later
+        private CanonicalNumberSerializerProvider _numberSerializerProvider = CanonicalBigDecimalSerializer.PROVIDER;
+        private boolean _enablePrettyPrinting = false;
+
+        private Builder() {
+            // Don't allow to create except via builder method
+        }
+
+        public Builder prettyPrint() {
+            _enablePrettyPrinting = true;
+            _numberSerializerProvider = PrettyBigDecimalSerializer.PROVIDER;
+            return this;
+        }
+
+        public JsonMapper build() {
+            CanonicalJsonFactory jsonFactory = new CanonicalJsonFactory(_numberSerializerProvider.getValueToString());
+            CanonicalJsonModule module = new CanonicalJsonModule(_numberSerializerProvider.getNumberSerializer());
+
+            JsonMapper.Builder builder = JsonMapper.builder(jsonFactory)
+                .enable(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS) //
+                .enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY) //
+                .addModule(module);
+
+            if (_enablePrettyPrinting) {
+                builder = builder //
+                    .enable(SerializationFeature.INDENT_OUTPUT) //
+                    .enable(StreamWriteFeature.WRITE_BIGDECIMAL_AS_PLAIN) //
+                    .defaultPrettyPrinter(CanonicalPrettyPrinter.INSTANCE) //
+                ;
+            }
+
+            return builder.build();
+        }
+    }
+
+    public static CanonicalJsonMapper.Builder builder() {
+        return new Builder();
+    }
+}

src/test/java/com/fasterxml/jackson/databind/ser/CanonicalJsonModule.java

@@ -0,0 +1,18 @@
+package com.fasterxml.jackson.databind.ser;
+
+import java.math.BigDecimal;
+
+import com.fasterxml.jackson.databind.module.SimpleModule;
+import com.fasterxml.jackson.databind.ser.std.StdSerializer;
+
+public class CanonicalJsonModule extends SimpleModule {
+    private static final long serialVersionUID = 1L;
+
+    public CanonicalJsonModule() {
+        this(CanonicalBigDecimalSerializer.INSTANCE);
+    }
+
+    public CanonicalJsonModule(StdSerializer<BigDecimal> numberSerializer) {
+        addSerializer(BigDecimal.class, numberSerializer);
+    }
+}