Java Reflection 访问公共字段

Question

我正在为 List 类编写一个自定义序列化程序(杰克逊 JSON(，这个列表可以用不同的类类型推断，所以我需要使用反射来获取对象字段值。

请注意，所有这些类都有公共值(没有 setter 和 getter(，因此调用 getter 将不是一种选择。

这是我到目前为止得到的：

package com.xxx.commons.my.serializer;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;
import org.apache.commons.lang3.reflect.FieldUtils;
import java.io.IOException;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.lang.reflect.Type;
import java.math.BigDecimal;
import java.util.List;
public class ListSerializer extends StdSerializer<List> {
public ListSerializer() {
    super(List.class);
}
@Override
public void serialize(List aList, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
    if (aList != null) {
        jsonGenerator.writeStartObject();
        for (int index = 0 ; index < aList.size(); index++) {
            try {
                Object next = aList.get(index);
                List<Field> fields = FieldUtils.getAllFieldsList(next.getClass());
                Object object = next.getClass().newInstance();
                for (int j = 0 ; j < fields.size(); j ++ ) {
                    jsonGenerator.writeObjectField(String.format("%s[%s]",fields.get(j).getName(),index) , object);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        jsonGenerator.writeEndObject();
    }
}
}

我的测试

package com.xxx.commons.my.serializer;
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.PropertyAccessor;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializationFeature;
import com.fasterxml.jackson.databind.module.SimpleModule;
import org.junit.Test;
public class ListSerializerTest {
    private ObjectMapper mapper = new ObjectMapper();
    @Test
    public void test() throws Exception {
        SimpleModule module = new SimpleModule();
        module.addSerializer(new ListSerializer());
        mapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
        mapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        mapper.registerModule(module);
        MyTempClassParent parent = new MyTempClassParent();
        parent.mylist.add(new MyTempClass("1","2","3"));
        String json = mapper.writeValueAsString(parent);
        System.out.println(json);
    }   
}

示例类：

public class MyTempClass {
    public MyTempClass() {
    }
    public MyTempClass(String value1, String value2, String value3) {
        this.valueA = value1;
        this.valueB = value2;
        this.valueC = value3;
    }
    public String valueA;
    public String valueB;
    public String valueC;
}
public class MyTempClassParent {
   public List<MyTempClass> mylist = new LinkedList<>();
}

写这个有什么想法或替代方案吗？

Answer 1

也许你应该使用带有设置属性访问器的ObjectMapper来访问每个字段：

ObjectMapper mapper = new ObjectMapper();
    mapper.setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY);
    MyDtoAccessLevel dtoObject = new MyDtoAccessLevel();
    String dtoAsString = mapper.writeValueAsString(Arrays.asList(dtoObject));
    System.out.println(dtoAsString);

结果：[{"stringValue"：null，"intValue"：0，"floatValue"：0.0，"booleanValue"：false}]目录：

class MyDtoAccessLevel {
    private String stringValue;
    int intValue;
    protected float floatValue;
    public boolean booleanValue;
    // NO setters or getters

--编辑对于通过反射从对象获取值：

    @Override
public void serialize(List aList, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
    if (aList != null) {
        jsonGenerator.writeStartObject();
        for (int index = 0 ; index < aList.size(); index++) {
            try {
                Object next = aList.get(index);
                List<Field> fields = FieldUtils.getAllFieldsList(next.getClass());
                for (int j = 0 ; j < fields.size(); j ++ ) {
                    jsonGenerator.writeObjectField(String.format("%s[%s]",fields.get(j).getName(),index) , fields.get(j).get(next));
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        jsonGenerator.writeEndObject();
    }
}

请写下有问题，您希望输出什么。