java - 如何在以下场景中为模型的特定字段选择自定义序列化器

Question

下面是两个自定义日期序列化器:

package test;
import java.io.IOException;
import java.sql.Date;
import java.text.SimpleDateFormat;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;

public class DateFormatter extends StdSerializer<Date> {

    private SimpleDateFormat sampleFormatOne= new SimpleDateFormat("dd-MMM-yyyy");


    public DateFormatter(Class<Date> t) {
        super(t);
    }

    public DateFormatter() {
        super(Date.class);
    }

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Override
    public void serialize(Date date, JsonGenerator jsonGenerator, SerializerProvider provider) throws IOException,
            JsonGenerationException {
        java.util.Date inputDate = new java.util.Date(date.getTime());

        jsonGenerator.writeString(sampleFormatOne.format(inputDate));
    }

}

还有另一个日期序列化器:

package test;
import java.io.IOException;
import java.sql.Date;
import java.text.SimpleDateFormat;

import com.fasterxml.jackson.core.JsonGenerationException;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.ser.std.StdSerializer;

public class DateFormatterTwo extends StdSerializer<Date> {

      private SimpleDateFormat samoelFormatTwo= new SimpleDateFormat("dd-mm-yyyy");y");

    public DateFormatterTwo (Class<Date> t) {
        super(t);
    }

    public DateFormatterTwo () {
        super(Date.class);
    }

    /**
     * 
     */
    private static final long serialVersionUID = 1L;

    @Override
    public void serialize(Date date, JsonGenerator jsonGenerator, SerializerProvider provider) throws IOException,
            JsonGenerationException {
        java.util.Date inputDate = new java.util.Date(date.getTime());

        jsonGenerator.writeString(samoelFormatTwo.format(inputDate));
    }

}

Spring配置如下:

<beans:bean id="customDate"
        class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
        <beans:property name="objectMapper">
            <beans:bean
                class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean">
                <beans:property name="serializers">
                    <beans:array>
                        <beans:bean class="test.DateFormatter" />
                        <beans:bean class="test.DateFormatterTwo" />
                    </beans:array>
                </beans:property>
            </beans:bean>
        </beans:property>
    </beans:bean>


    <beans:bean
        class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
        <beans:property name="messageConverters">
            <beans:list>
                <beans:ref bean="jsonMessageConverter" />
                <beans:ref bean="customDate" />
            </beans:list>
        </beans:property>
    </beans:bean>

现在我需要做的是创建一个 JSON 对象，该对象基于 f irst or second formatter 进行日期序列化取决于字段值employeeType 的值。

通过当前的实现，我可以生成具有固定第一个格式的 JSON。 如何在运行时根据另一个字段值选择序列化器。 ？

以下是模型中的字段

private field String employeeType;

    @JsonProperty("empJoiningDate")
    @JsonSerialize(using=DateFormatter.class)
    private Date empJoiningDate = null; 

Answer 1

为了使用取决于 employeeType 的格式序列化 empJoiningDate 字段，您需要为Employee POJO 类型而不是 Date 字段。

按照这种方法，您将可以访问所有对象字段，并可以提供条件日期序列化逻辑。

Serializer 实现如下:

private static class EmployeeSerializer extends StdSerializer<Employee> {

    private static final String TYPE_ONE = "SomeType";

    private static final String TYPE_TWO = "SomeOtherType";

    private SimpleDateFormat sampleFormatOne = /** format initialized **/;

    private SimpleDateFormat sampelFormatTwo = /** format initialized **/;

    protected EmployeeSerializer() {
        super(Employee.class);
    }

    @Override
    public void serialize(Employee employee, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
        jsonGenerator.writeStartObject();
        jsonGenerator.writeString(employee.getEmployeeType());
        switch (employee.getEmployeeType()) {
            case TYPE_ONE: jsonGenerator.writeString(sampleFormatOne.format(employee.getEmpJoiningDate()));
            case TYPE_TWO: jsonGenerator.writeString(sampelFormatTwo.format(employee.getEmpJoiningDate()));
        }
        jsonGenerator.writeEndObject();
    }
}

然后，您需要使用自定义序列化程序而不是实例日期字段来注释您的 Employee 值类:

@JsonSerialize(using = EmployeeSerializer.class)
public class Employee {
    //...
}