Spring 验证字符串值是一个 JSON [英] Spring validate string value is a JSON

问题描述

我的配置文件中有一些值，它应该是一个 JSON(将作为字符串加载).

I have some value from my configuration file, that should be a JSON (which will be loaded as a String).

我希望 Spring 在注入之前验证该值确实是有效的 JSON，否则会引发错误.

I'd like Spring to validate that this value is indeed a valid JSON before injecting it and throw an error else.

我已经阅读了存在的验证注释，例如 - @NotNull、@Size、@Min、@Max、@Email、@NotEmpty 等

I've read about the validation annotations that exist, such as - @NotNull, @Size, @Min, @Max, @Email, @NotEmpty etc.

有没有办法创建自定义验证器?

Is there any way to create a custom validator?

我想要一个尝试将字符串转换为 JSON 的验证器，如下例所示:Java 中如何将 jsonString 转换为 JSONObject.

I want a validator that will attempt to convert the String to JSON, as in the following example: How to convert jsonString to JSONObject in Java.

推荐答案

这不是由可用的验证注释提供的，因此您必须寻求自定义实现.任务分为两个简单的步骤:

This is not provided by available validation annotations, therefore you have to go for a custom implementation. The task is divided into 2 simple steps:

1.给定的 String 是否为 JSON 格式

有多个库可以解析(因此验证)字符串是否遵循 JSON 语法标准.让我们以我最喜欢的 GSON 为例(有 许多).这取决于您当前使用的库:

There are multiple libraries that are able to parse (therefore validate) a String whether follows the JSON syntax standard. Let's use my favourite GSON for example (there are many). It depends on what library do you currently use:

String string = "{\"foo\":\"bar\"}"
JsonParser jsonParser = new JsonParser();
try {
    jsonParser.parse(string);       // valid JSON
} catch (JsonSyntaxException ex) { 
    /* exception handling */        // invalid JSON
}

2.自定义验证注释

从提供启用验证的依赖项开始:

Start with providing a dependency enabling validations:

• groupId:org.hibernate
• artifactId:hibernate-validator

创建用于验证的注释:

@Documented
@Constraint(validatedBy = JsonStringValidator.class)
@Target({ ElementType.FIELD })
@Retention(RetentionPolicy.RUNTIME)
public @interface JsonString {
    String message() default "The String is not in JSON format";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

... 以及通过注解处理验证的验证器:

... and the validator handling the validation through the annotation:

public class JsonStringValidator implements ConstraintValidator<JsonString, String> {

    @Override
    public void initialize(JsonString jsonString) { }

    @Override
    public boolean isValid(String string, ConstraintValidatorContext context) {
        // Use an implementation from step 1. A brief example:
        try {
            new JsonParser().parse(string);
            return true;                    // valid JSON, return true
        } catch (JsonSyntaxException ex) { 
            /* exception handling if needed */
        }
        return false;                       // invalid JSON, return false
    }
}

用法非常简单:

@JsonString
private String expectedJsonString

Baeldung's 中详细描述了此实现.

This implementation is described in detail at Baeldung's.

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