Attempt to provide a built-in WriteNonStringValueAsString serializer …

[jujn]

…for base types, for issue #3870

What this PR does / why we need it?

是否可以提供如下功能：
对基础类型提供内置 NonStringValueAsString 序列化器；
方便用户全局注册。

尝试了一种实现方式（草稿，感觉不太好，无法避免装箱拆箱），跑了 BenchMark 程序和结果如下：

点击查看 benchmark 代码

package com.alibaba.fastjson2.benchmark;

import com.alibaba.fastjson2.JSON;
import com.alibaba.fastjson2.JSONWriter;
import com.alibaba.fastjson2.writer.ObjectWriterAsString;
import com.alibaba.fastjson2.writer.ObjectWriterProvider;
import org.openjdk.jmh.annotations.*;
import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.runner.Runner;
import org.openjdk.jmh.runner.RunnerException;
import org.openjdk.jmh.runner.options.Options;
import org.openjdk.jmh.runner.options.OptionsBuilder;

import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@State(Scope.Thread)
@Fork(3) 
@Warmup(iterations = 5, time = 5) 
@Measurement(iterations = 5, time = 5)
public class AsStringBenchmark {

    public static class PrimitiveBean {
        public int vInt;
        public long vLong;
        public float vFloat;
        public double vDouble;
        public short vShort;
        public byte vByte;
        public boolean vBoolean;
        public char vChar;
        public Integer vInteger;
        public Long vLongWrapper;
        public Float vFloatWrapper;
        public Double vDoubleWrapper;
        public Short vShortWrapper;
        public Byte vByteWrapper;
        public Boolean vBooleanWrapper;
        public Character vCharWrapper;
        public BigInteger vBigInteger;
        public BigDecimal vBigDecimal;
        public int[] vIntArray;
        public long[] vLongArray;
        public float[] vFloatArray;
        public double[] vDoubleArray;
        public short[] vShortArray;
        public byte[] vByteArray;
        public boolean[] vBooleanArray;

        public PrimitiveBean() {
            this.vInt = 10086;
            this.vLong = 1678888888888L;
            this.vFloat = 123.456f;
            this.vDouble = 3.1415926;
            this.vShort = (short) 123;
            this.vByte = (byte) 127;
            this.vBoolean = true;
            this.vChar = 'A';

            this.vInteger = 999;
            this.vLongWrapper = 54321L;
            this.vFloatWrapper = 67.89f;
            this.vDoubleWrapper = 0.9999;
            this.vShortWrapper = (short) 456;
            this.vByteWrapper = (byte) -1;
            this.vBooleanWrapper = Boolean.FALSE;
            this.vCharWrapper = 'Z';

            this.vBigInteger = new BigInteger("12345678901234567890");
            this.vBigDecimal = new BigDecimal("12345.67890123456789");

            this.vIntArray = new int[]{1, 2, 3, 4, 5};
            this.vLongArray = new long[]{100L, 200L, 300L, 400L, 500L};
            this.vFloatArray = new float[]{1.1f, 2.2f, 3.3f, 4.4f, 5.5f};
            this.vDoubleArray = new double[]{1.11, 2.22, 3.33, 4.44, 5.55};
            this.vShortArray = new short[]{10, 20, 30, 40, 50};
            this.vByteArray = new byte[]{0, 1, 2, 3, 4};
            this.vBooleanArray = new boolean[]{true, false, true, true, false};
        }
    }

    private PrimitiveBean bean;
    private JSONWriter.Context defaultContext;
    private JSONWriter.Context asStringContext;

    @Setup
    public void setup() {
        bean = new PrimitiveBean();

        ObjectWriterProvider customProvider0 = new ObjectWriterProvider();
        defaultContext = new JSONWriter.Context(customProvider0);
        defaultContext.config(JSONWriter.Feature.WriteNonStringValueAsString);


        ObjectWriterProvider customProvider = new ObjectWriterProvider();

        customProvider.register(int.class, ObjectWriterAsString.OF_INT_VALUE);
        customProvider.register(long.class, ObjectWriterAsString.OF_LONG_VALUE);
        customProvider.register(float.class, ObjectWriterAsString.OF_FLOAT_VALUE);
        customProvider.register(double.class, ObjectWriterAsString.OF_DOUBLE_VALUE);
        customProvider.register(short.class, ObjectWriterAsString.OF_SHORT_VALUE);
        customProvider.register(byte.class, ObjectWriterAsString.OF_BYTE_VALUE);
        customProvider.register(boolean.class, ObjectWriterAsString.OF_BOOLEAN_VALUE);
        customProvider.register(char.class, ObjectWriterAsString.OF_CHAR_VALUE);

        customProvider.register(Integer.class, ObjectWriterAsString.OF_INTEGER);
        customProvider.register(Long.class, ObjectWriterAsString.OF_LONG);
        customProvider.register(Float.class, ObjectWriterAsString.OF_FLOAT);
        customProvider.register(Double.class, ObjectWriterAsString.OF_DOUBLE);
        customProvider.register(Short.class, ObjectWriterAsString.OF_SHORT);
        customProvider.register(Byte.class, ObjectWriterAsString.OF_BYTE);
        customProvider.register(Boolean.class, ObjectWriterAsString.OF_BOOLEAN);
        customProvider.register(Character.class, ObjectWriterAsString.OF_CHARACTER);

        customProvider.register(BigInteger.class, ObjectWriterAsString.OF_BIG_INTEGER);
        customProvider.register(BigDecimal.class, ObjectWriterAsString.OF_BIG_DECIMAL);

        customProvider.register(int[].class, ObjectWriterAsString.OF_INT_ARRAY);
        customProvider.register(long[].class, ObjectWriterAsString.OF_LONG_ARRAY);
        customProvider.register(float[].class, ObjectWriterAsString.OF_FLOAT_ARRAY);
        customProvider.register(double[].class, ObjectWriterAsString.OF_DOUBLE_ARRAY);
        customProvider.register(short[].class, ObjectWriterAsString.OF_SHORT_ARRAY);
        customProvider.register(byte[].class, ObjectWriterAsString.OF_BYTE_ARRAY);
        customProvider.register(boolean[].class, ObjectWriterAsString.OF_BOOLEAN_ARRAY);

        asStringContext = new JSONWriter.Context(customProvider);
    }

    @Benchmark
    public void baseline_native_numbers(Blackhole bh) {
        bh.consume(JSON.toJSONString(bean, defaultContext));
    }

    @Benchmark
    public void target_as_string(Blackhole bh) {
        bh.consume(JSON.toJSONString(bean, asStringContext));
    }

    public static void main(String[] args) throws RunnerException {
        Options opt = new OptionsBuilder()
                .include(AsStringBenchmark.class.getSimpleName())
                .addProfiler("gc")
                .build();
        new Runner(opt).run();
    }
}

jdk21-asm（fastjson2.creator=asm）：

jdk17-asm：

jdk8-asm：

[Copilot]

Pull request overview

This PR introduces built-in serializers for base types to support the WriteNonStringValueAsString feature, addressing issue #3870. The implementation provides convenience for users who want to globally register serializers that write numeric and boolean values as strings.

Key Changes:

• Adds a new ObjectWriterAsString class with pre-defined serializer instances for primitive types, wrapper classes, BigInteger, BigDecimal, and primitive arrays
• Updates ObjectWriterCreator.getInitWriter() to recognize and use registered ObjectWriterAsString instances
• Refines import statement in ObjectWriterCreator from wildcard to specific import

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
core/src/main/java/com/alibaba/fastjson2/writer/ObjectWriterAsString.java	Introduces abstract class with 18 static serializer instances for converting base types to string representations during JSON serialization
core/src/main/java/com/alibaba/fastjson2/writer/ObjectWriterCreator.java	Adds logic to detect and return ObjectWriterAsString instances in the else block of getInitWriter method; refines filter import

---

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[Copilot]

The instanceof check should use pattern matching or avoid redundant null check. Since this code checks if objectWriter is not null implicitly through the cache.get() call, the instanceof check will return false for null values anyway, making the explicit null check redundant. Consider simplifying to just check the instanceof condition.

Suggested change

	if (objectWriter != null && objectWriter instanceof ObjectWriterAsString) {
	if (objectWriter instanceof ObjectWriterAsString) {

[Copilot]

The class and its public static fields lack documentation. Since this is a public API that users will directly interact with to register custom serializers, comprehensive JavaDoc should be added to explain the purpose of this class, when to use it, and provide usage examples. Each public static field should also have documentation explaining what type it serializes.

[Copilot]

The error message references the base class method but doesn't provide actionable guidance. Consider updating the message to explain that users should use the specific static instances (e.g., OF_INTEGER, OF_LONG) instead of calling the base write method directly, and provide an example of correct usage.

Suggested change

	throw new JSONException("ObjectWriterAsString.write() should NOT be called directly: "
	+ object.getClass().getName());
	throw new JSONException(
	"ObjectWriterAsString.write() should NOT be called directly for type: "
	+ object.getClass().getName()
	+ ".\n"
	+ "Please use one of the specific static instances (e.g., ObjectWriterAsString.OF_INTEGER, ObjectWriterAsString.OF_LONG) instead.\n"
	+ "Example: ObjectWriterAsString.OF_INTEGER.write(jsonWriter, value, fieldName, fieldType, features);"
	);

[Copilot]

The new ObjectWriterAsString class lacks test coverage. Since this is a new public API that provides built-in serializers for base types, tests should be added to verify that each serializer instance correctly serializes values as strings, handles null values properly, and integrates correctly when registered with ObjectWriterProvider. Consider adding tests that cover scenarios like registering these writers globally and verifying their usage through the ObjectWriterCreator.getInitWriter method.

[wenshao]

建议在BigDecimal/BigInteger这两个类型的Writer实现中支持WriteNonStringValueAsString，这样改动小，用户使用也更方便

[jujn]

建议在BigDecimal/BigInteger这两个类型的Writer实现中支持WriteNonStringValueAsString，这样改动小，用户使用也更方便

这两个序列化器目前是支持 WriteNonStringValueAsString 的：

    @Test
    public void test() {
        System.out.println(JSON.toJSONString(new Model(BigInteger.valueOf(123), BigDecimal.valueOf(456)), JSONWriter.Feature.WriteNonStringValueAsString));
        // asm、reflect模式下都会输出 {"age":"456","name":"123"}
    }

    @Data
    public static class Model {
        private BigInteger name;
        private BigDecimal age;
    }

用户意思想 ”一条配置，全局BigInteger/BigDecimal都序列化为字符串“，类似的问题#3563、#891也提到过（全局配置BooleanAsString不生效）