您需要实现自定义序列化程序，在其中需要计算已经处理的
Node对象的数量。对于每个序列化过程，我们需要在
maxdepth每次
Node发现类时提供值并递减值。示例实现：
import com.fasterxml.jackson.core.JsonGenerator;import com.fasterxml.jackson.core.JsonProcessingException;import com.fasterxml.jackson.databind.BeanDescription;import com.fasterxml.jackson.databind.JsonSerializer;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.ObjectWriter;import com.fasterxml.jackson.databind.SerializationConfig;import com.fasterxml.jackson.databind.SerializationFeature;import com.fasterxml.jackson.databind.SerializerProvider;import com.fasterxml.jackson.databind.json.JsonMapper;import com.fasterxml.jackson.databind.module.SimpleModule;import com.fasterxml.jackson.databind.ser.BeanSerializer;import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;import com.fasterxml.jackson.databind.ser.std.BeanSerializerbase;import java.io.IOException;import java.util.concurrent.atomic.AtomicInteger;public class JsonApp { public static void main(String[] args) throws IOException { Node nodeD = new Node("D", null); Node nodeC = new Node("C", nodeD); Node nodeB = new Node("B", nodeC); Node nodeA = new Node("A", nodeB); for (int i = 0; i < 4; i++) { System.out.println("Depth: " + i); System.out.println(serialiseWithDepth(nodeA, i)); } } private static ObjectMapper mapper = JsonMapper.builder() .enable(SerializationFeature.INDENT_OUTPUT) .addModule(createNodeModule()) .build(); private static String serialiseWithDepth(Node node, int maxDepth) throws JsonProcessingException { ObjectWriter writer = mapper.writerFor(Node.class) .withAttribute(NodeDepthBeanSerializer.DEPTH_KEY, new AtomicInteger(maxDepth)); return writer.writevalueAsString(node); } private static SimpleModule createNodeModule() { SimpleModule nodeModule = new SimpleModule("NodeModule"); nodeModule.setSerializerModifier(new BeanSerializerModifier() { @Override public JsonSerializer<?> modifySerializer(SerializationConfig config, BeanDescription beanDesc, JsonSerializer<?> serializer) { if (beanDesc.getBeanClass() == Node.class) { return new NodeDepthBeanSerializer((BeanSerializerbase) serializer); } return super.modifySerializer(config, beanDesc, serializer); } }); return nodeModule; }}class NodeDepthBeanSerializer extends BeanSerializer { public static final String DEPTH_KEY = "maxDepthSize"; public NodeDepthBeanSerializer(BeanSerializerbase src) { super(src); } @Override protected void serializeFields(Object bean, JsonGenerator gen, SerializerProvider provider) throws IOException { AtomicInteger depth = (AtomicInteger) provider.getAttribute(DEPTH_KEY); if (depth.decrementAndGet() >= 0) { super.serializeFields(bean, gen, provider); } }}上面的代码打印：
Depth: 0Node{id='A', child=Node{id='B', child=Node{id='C', child=Node{id='D', child=null}}}} => 0{ }Depth: 1Node{id='A', child=Node{id='B', child=Node{id='C', child=Node{id='D', child=null}}}} => 1Node{id='B', child=Node{id='C', child=Node{id='D', child=null}}} => 0{ "id" : "A", "child" : { }}Depth: 2Node{id='A', child=Node{id='B', child=Node{id='C', child=Node{id='D', child=null}}}} => 2Node{id='B', child=Node{id='C', child=Node{id='D', child=null}}} => 1Node{id='C', child=Node{id='D', child=null}} => 0{ "id" : "A", "child" : { "id" : "B", "child" : { } }}Depth: 3Node{id='A', child=Node{id='B', child=Node{id='C', child=Node{id='D', child=null}}}} => 3Node{id='B', child=Node{id='C', child=Node{id='D', child=null}}} => 2Node{id='C', child=Node{id='D', child=null}} => 1Node{id='D', child=null} => 0{ "id" : "A", "child" : { "id" : "B", "child" : { "id" : "C", "child" : { } } }}
