Json反序列化到URL（拦截）

Question

尝试反序列化URL时出现此错误

Caused by: java.net.MalformedURLException: no protocol: www.boo.com
    at java.net.URL.<init>(URL.java:586) ~[na:1.8.0_45]
    at java.net.URL.<init>(URL.java:483) ~[na:1.8.0_45]
    at java.net.URL.<init>(URL.java:432) ~[na:1.8.0_45]
    at com.fasterxml.jackson.databind.deser.std.FromStringDeserializer$Std._deserialize(FromStringDeserializer.java:212) ~[jackson-databind-2.6.2.jar:2.6.2]
    at com.fasterxml.jackson.databind.deser.std.FromStringDeserializer.deserialize(FromStringDeserializer.java:122) ~[jackson-databind-2.6.2.jar:2.6.2]
    at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:520) ~[jackson-databind-2.6.2.jar:2.6.2]
    at com.fasterxml.jackson.databind.deser.impl.MethodProperty.deserializeAndSet(MethodProperty.java:95) ~[jackson-databind-2.6.2.jar:2.6.2]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:337) ~[jackson-databind-2.6.2.jar:2.6.2]
    at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:131) ~[jackson-databind-2.6.2.jar:2.6.2]
    at com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:245) ~[jackson-databind-2.6.2.jar:2.6.2]

波乔：

class foo {
   ...
   URL url
   ...
}

正如错误所说，如果缺少协议，如果用户没有设置协议，如何在反序列化之前插入协议？

Answer 1

您可以使用自定义反序列化器（参见另一个答案）。另一个解决方案——不那么优雅，但很简单——是在您的bean中创建一个接受String值的setter，并在创建URL对象之前在内部做一些准备：

private Pattern urlPrefix = Pattern.compile("^(https?://|ftp://).*"); //etc.
//...
public void setUrl(String url) {
    if (url != null && urlPrefix.matcher(url).matches()) {
        this.url = new URL(url);
    } else {
        this.url = new URL("http://" + url);
    }
}

Answer 2

您可以使用自定义反序列化器。有关自定义反序列化器的用法，请参阅此处的自定义JSON反序列化

Answer 3

我结合了之前的两个答案：

public class Foo {
   ...
   @JsonDeserialize(using = UrlDeseralizer.class)
   private URL url;
   ...
}

public class UrlDeseralizer extends JsonDeserializer<URL> {

    private Pattern urlPrefix = Pattern.compile("^(https?://|ftp://).*");

    @Override
    public URL deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        ObjectCodec objectCodec = p.getCodec();
        JsonNode node = objectCodec.readTree(p);
        String stringUrl = node.asText();
        if (!urlPrefix.matcher(stringUrl).matches()) {
            return new URL("http://" + stringUrl);
        } else {
            return new URL(stringUrl);
        }
    }

}