Custom deserializer for requests with content-type application/x-www-form-urlencoded in Spring Boot

问题

I want to write a custom deserializer for some parameters in the requests of type application/x-www-form-urlencoded like used in case of requests of type application/json, with @JsonDeserialize(using = AbcDeserializer.class) annotation. I am using spring boot and Jackson, although I figured out that Jackson is not used here.

I tried figuring out how spring deserializes object by default. But couldn't find a way.

How does spring deserialize a request of type application/x-www-form-urlencoded by default?

Can I override this deserialization, preferrably by using some annotation on parameters that need special handling?

回答1:

My solution is based on custom ConditionalGenericConverter. It works with @ModelAttribute. Let's see whole implementation.

Application bootstrap example.

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Configuration;
import org.springframework.format.FormatterRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@SpringBootApplication
public class DemoApplication {

    @Configuration
    public class WebConfig extends WebMvcConfigurerAdapter {

        @Override
        public void addFormatters(FormatterRegistry registry) {
            registry.addConverter(new Base64JsonToObjectConverter());
        }
    }

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

Here is custom annotation.

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

@Retention(RetentionPolicy.RUNTIME)
public @interface Base64Encoded {
}

Next we need implementation of the converter. As you can see, converter converts only String -> Object, where Object field must be annotated with Base64Encoded annotation.

import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.core.convert.ConversionFailedException;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.core.convert.converter.ConditionalGenericConverter;
import org.springframework.stereotype.Component;

import java.io.IOException;
import java.util.Base64;
import java.util.Collections;
import java.util.Set;

@Component
public class Base64JsonToObjectConverter implements ConditionalGenericConverter {

    private final ObjectMapper objectMapper;
    private final Base64.Decoder decoder;

    public Base64JsonToObjectConverter() {
        this.objectMapper = new ObjectMapper();
        this.decoder = Base64.getDecoder();
    }

    @Override
    public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
        return targetType.hasAnnotation(Base64Encoded.class);
    }

    @Override
    public Set<ConvertiblePair> getConvertibleTypes() {
        return Collections.singleton(new ConvertiblePair(String.class, Object.class));
    }

    @Override
    public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
        if (source == null) {
            return null;
        }
        String string = (String) source;

        try {
            byte[] decodedValue = this.decoder.decode(string);

            return this.objectMapper.readValue(decodedValue, targetType.getType());
        } catch (IllegalArgumentException | IOException e) {
            throw new ConversionFailedException(sourceType, targetType, source, e);
        }
    }
}

Here is an example of POJO (see the annotated field) and REST controller.

import com.example.demo.Base64Encoded;

public class MyRequest {

    private String varA;

    @Base64Encoded
    private B varB;

    public String getVarA() {
        return varA;
    }

    public void setVarA(String varA) {
        this.varA = varA;
    }

    public B getVarB() {
        return varB;
    }

    public void setVarB(B varB) {
        this.varB = varB;
    }
}

import com.example.demo.domain.MyRequest;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class DemoController {

    @RequestMapping(path = "/test", method = RequestMethod.POST)
    public MyRequest test(@ModelAttribute MyRequest myRequest) {
        return myRequest;
    }
}

来源：https://stackoverflow.com/questions/44384557/custom-deserializer-for-requests-with-content-type-application-x-www-form-urlenc

标签

java

Spring

spring-mvc

spring-boot

deserialization