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fastjson2自定义注解

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FASTJSON 2是一个性能极致并且简单易用的Java JSON库。

貌似中文互联网上还没有相关的教程。稍微看了下fastjson2的实现，相较于fastjson还是有很大改动的。

自定义注解，在处理定制化逻辑，例如：ID混淆、数据转换、RPC等场景时还是比较实用的。

下面就写一个简单的demo。

Java

自定义注解

实现一个自定义JSON字段名称的功能

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/**
 * @author yhzdys
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface JSONField2 {

    String value();
}

自定义 ObjectWriter

单独识别上面我们自定义的注解

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import com.alibaba.fastjson2.codec.BeanInfo;
import com.alibaba.fastjson2.codec.FieldInfo;
import com.alibaba.fastjson2.modules.ObjectWriterAnnotationProcessor;
import com.alibaba.fastjson2.util.BeanUtils;
import com.alibaba.fastjson2.writer.ObjectWriterBaseModule;
import com.alibaba.fastjson2.writer.ObjectWriterProvider;

import java.lang.reflect.Field;
import java.lang.reflect.Method;

/**
 * @author yhzdys 
 */
final class JSONFieldWriter extends ObjectWriterBaseModule {

    private final ObjectWriterAnnotationProcessor processor;

    JSONFieldWriter(ObjectWriterProvider provider) {
        super(provider);
        final ObjectWriterAnnotationProcessor processor = super.getAnnotationProcessor();
        this.processor = new ObjectWriterAnnotationProcessor() {

            @Override
            public void getBeanInfo(final BeanInfo beanInfo, final Class objectClass) {
                processor.getBeanInfo(beanInfo, objectClass);
            }

            @Override
            public void getFieldInfo(final BeanInfo beanInfo, final FieldInfo fieldInfo, final Class objectClass, final Field field) {
                final JSONField2 annotation = field.getAnnotation(JSONField2.class);
                if (annotation == null) {
                    processor.getFieldInfo(beanInfo, fieldInfo, objectClass, field);
                } else {
                    fieldInfo.ignore = false;
                    fieldInfo.fieldClassMixIn = false;
                    fieldInfo.fieldName = annotation.value();
                }
            }

            @Override
            public void getFieldInfo(final BeanInfo beanInfo, final FieldInfo fieldInfo, final Class objectClass, final Method method) {
                if (objectClass.getName().startsWith("java.lang") || BeanUtils.isRecord(objectClass)) {
                    processor.getFieldInfo(beanInfo, fieldInfo, objectClass, method);
                    return;
                }
                final Field field = BeanUtils.getField(objectClass, method);
                if (field == null) {
                    processor.getFieldInfo(beanInfo, fieldInfo, objectClass, method);
                    return;
                }
                fieldInfo.features |= FieldInfo.FIELD_MASK;
                this.getFieldInfo(beanInfo, fieldInfo, objectClass, field);
            }
        };
    }

    @Override
    public ObjectWriterAnnotationProcessor getAnnotationProcessor() {
        return this.processor;
    }
}

自定义 ObjectReader

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import com.alibaba.fastjson2.codec.FieldInfo;
import com.alibaba.fastjson2.reader.ObjectReaderBaseModule;
import com.alibaba.fastjson2.reader.ObjectReaderProvider;

import java.lang.reflect.Field;

/**
 * @author yhzdys 
 */
final class JSONFieldReader extends ObjectReaderBaseModule {

    JSONFieldReader(ObjectReaderProvider provider) {
        super(provider);
    }

    @Override
    public void getFieldInfo(final FieldInfo fieldInfo, final Class objectClass, final Field field) {
        final JSONField2 annotation = field.getAnnotation(JSONField2.class);
        if (annotation == null) {
            super.getFieldInfo(fieldInfo, objectClass, field);
            return;
        }
        fieldInfo.ignore = false;
        fieldInfo.fieldClassMixIn = false;
        fieldInfo.fieldName = annotation.value();
    }
}

注册自定义的 ObjectWriter 和 ObjectReader

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import com.alibaba.fastjson2.JSONFactory;
import com.alibaba.fastjson2.reader.ObjectReaderProvider;
import com.alibaba.fastjson2.writer.ObjectWriterProvider;

public class Test {

    static {
        final ObjectReaderProvider readerProvider = JSONFactory.getDefaultObjectReaderProvider();
        readerProvider.getModules().clear();
        readerProvider.register(new JSONFieldReader(readerProvider));

        final ObjectWriterProvider writerProvider = JSONFactory.getDefaultObjectWriterProvider();
        writerProvider.getModules().clear();
        writerProvider.register(new JSONFieldWriter(writerProvider));
    }
}

完工

以上demo仅供参考。需根据实际情况调整。