Spring MVC 中@RequestParam 的自定义转换器 [英] Custom converter for @RequestParam in Spring MVC

问题描述

我正在获取一个加密字符串作为 Spring rest 控制器方法的查询参数.

I am getting an encrypted String as Query parameter to a Spring rest controller method.

我想在字符串到达​​基于一些注释(比如@Decrypt)的方法之前解密字符串

I wanted to decrypt the string before it reaches the method based on some annotation (say @Decrypt) like below

@RequestMapping(value = "/customer", method = RequestMethod.GET)
public String getAppointmentsForDay(@RequestParam("secret") @Decrypt String customerSecret) {
    System.out.println(customerSecret);  // Needs to be a decrypted value.
   ...
}

自定义Formatter 在这个用例中是正确的方法吗?

Is a custom Formatter the right approach in this use case?

或者我应该使用自定义的HandlerMethodArgumentResolver?

Or should I use a custom HandlerMethodArgumentResolver?

推荐答案

org.springframework.format.Formatter 的自定义实现是此用例的有效方法.这就是 Spring 本身为日​​期、货币、数字样式等实现格式化程序的方式.

A custom implementation of org.springframework.format.Formatter is a valid approach for this use case. This is how Spring itself implements formatters for dates, currencies, number styles etc.

步骤:

1. 声明一个注解:Decrypt:

import java.lang.annotation.*;

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER, ElementType.ANNOTATION_TYPE})
public @interface Decrypt {

}

声明一个使用新注解的AnnotationFormatterFactory:

import org.springframework.context.support.EmbeddedValueResolutionSupport;
import org.springframework.format.AnnotationFormatterFactory;
import org.springframework.format.Formatter;
import org.springframework.format.Parser;
import org.springframework.format.Printer;

import java.text.ParseException;
import java.util.Collections;
import java.util.HashSet;
import java.util.Locale;
import java.util.Set;

public class DecryptAnnotationFormatterFactory extends EmbeddedValueResolutionSupport
        implements AnnotationFormatterFactory<Decrypt> {

    @Override
    public Set<Class<?>> getFieldTypes() {
        Set<Class<?>> fieldTypes = new HashSet<>();
        fieldTypes.add(String.class);
        return Collections.unmodifiableSet(fieldTypes);
    }

    @Override
    public Printer<String> getPrinter(Decrypt annotation, Class<?> fieldType) {
        return configureFormatterFrom(annotation);
    }

    @Override
    public Parser<String> getParser(Decrypt annotation, Class<?> fieldType) {
        return configureFormatterFrom(annotation);
    }

    private Formatter<String> configureFormatterFrom(Decrypt annotation) {
        // you could model something on the Decrypt annotation for use in the decryption call
        // in this example the 'decryption' call is stubbed, it just reverses the given String
        // presumaby you implementaion of this Formatter will be different e.g. it will invoke your encryption routine
        return new Formatter<String>() {
            @Override
            public String print(String object, Locale locale) {
                return object;
            }

            @Override
            public String parse(String text, Locale locale) throws ParseException {
                return new StringBuilder(text).reverse().toString();
            }
        };
    }
}

在您的网络环境中注册这个格式化工厂:

Register this formatter factory with your web context:

import org.springframework.context.annotation.Configuration;
import org.springframework.format.FormatterRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration
public class WebConfigurer extends WebMvcConfigurerAdapter {
    @Override
    public void addFormatters(FormatterRegistry registry) {
        super.addFormatters(registry);
        registry.addFormatterForFieldAnnotation(new DecryptAnnotationFormatterFactory());
    }
}

就是这样.

That's it.

有了上述内容，所有使用 @Decrypt 限定的 @RequestParam 的用法都将通过 parse()DecryptAnnotationFormatterFactory 中声明的方法，以便您可以在那里实现您的解密调用.

With the above in place, all usages of a @RequestParam which are qualified with @Decrypt will be passed through the parse() method declared in DecryptAnnotationFormatterFactory so you can implement your decryption call there.

为了证明这一点，以下测试通过:

To prove this, the following test passes:

@RunWith(SpringRunner.class)
@WebMvcTest(controllers = YourController.class)
public class YourControllerTest {
    @Autowired
    private MockMvc mockMvc;

    @Test
    public void theSecretRequestParameterWillBeConverted() throws Exception {
        MvcResult mvcResult = mockMvc.perform(get("/customer?secret=abcdef")).andExpect(status().isOk()).andReturn();

        // the current implementation of the 'custom' endpoint returns the value if the secret request parameter and
        // the current decrypt implementation just reverses the given value ...
        assertThat(mvcResult.getResponse().getContentAsString(), is("fedcba"));
    }
}

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