CustomNullValueMapper.java

/**
 * 
 */
package com.vip.saturn.job.console.response.converter;

import java.io.IOException;
import java.lang.reflect.Type;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JavaType;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.jsonFormatVisitors.JsonFormatVisitorWrapper;
import com.fasterxml.jackson.databind.module.SimpleModule;
import com.fasterxml.jackson.databind.ser.DefaultSerializerProvider;
import com.fasterxml.jackson.databind.ser.std.NonTypedScalarSerializerBase;

/**
 * 返回json中null值显示为空
 * @author chembo.huang
 *
 */

public class CustomNullValueMapper extends ObjectMapper {
	
	private static final long serialVersionUID = 1L;

	class CustomStringSerializer extends NonTypedScalarSerializerBase<String>
	{
	    public CustomStringSerializer() { super(String.class); }

	    @Override
	    public boolean isEmpty(String value) {
	        return (value == null) || (value.length() == 0);
	    }
	    
	    @Override
	    public void serialize(String value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
	        jgen.writeString(value == null?"":("null".equals(value)?"":value));
	    }

	    @Override
	    public JsonNode getSchema(SerializerProvider provider, Type typeHint) {
	        return createSchemaNode("string", true);
	    }
	    
	    @Override
	    public void acceptJsonFormatVisitor(JsonFormatVisitorWrapper visitor, JavaType typeHint) throws JsonMappingException {
	        if (visitor != null) visitor.expectStringFormat(typeHint);
	    }
	}
	
	public CustomNullValueMapper() {
		DefaultSerializerProvider sp = new DefaultSerializerProvider.Impl();
		sp.setNullValueSerializer(new JsonSerializer<Object>() {
			
			@Override
			public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider)
					throws IOException, JsonProcessingException {
				jgen.writeString("");
			}
		});
		setSerializerProvider(sp);
		SimpleModule module = new SimpleModule();
		module.addSerializer(String.class, new CustomStringSerializer());
		registerModule(module);
	}
}