java - 使用 Jackson 与自定义逻辑绑定(bind) JSON 数据

Question

我已经定义了 JSON 响应，我想将其反序列化为 Java 对象。我设法使用树模型“手动”完成此操作，但如果可能的话我想使用数据绑定(bind)。问题是我的某些部分需要一些自定义逻辑。

JSON 如下所示:

{
    "resourcedescriptions": [
        {
            "path": "somePath",
            "tag_pagetype": "default",
            "tag_bookingcenter": [
                "bc_ch",
                "bc_de"
            ],
            "resources": [
                {
                    "path": "somePathDe.html",
                    "lang": "de",
                    "lastmodified": 1399020442914,
                    "mimetype": "text/html"
                },
                {
                    "path": "somePathEn.html",
                    "lang": "en",
                    "lastmodified": 1399907224208,
                    "mimetype": "text/html"
                }
            ],
            "lastmodified": 1399907224208
        },
        {
            "path": "someOtherPath",
            "tag_pagetype": "special",
            "tag_bookingcenter": [
                "bc_ch"
            ],
            "resources": [
                {
                    "path": "someOtherPathDe.html",
                    "lang": "de",
                    "lastmodified": 1399020442914,
                    "mimetype": "text/html"
                },
                {
                    "path": "someOtherPathEn.html",
                    "lang": "en",
                    "lastmodified": 1399907224208,
                    "mimetype": "text/html"
                }
            ],
            "lastmodified": 1399907224208
        }
    ]
}

我的 Java 类是:

public class ResourceDescription {
    private String path;
    private LocalDateTime lastModified;
    private String chartConfig;
    private final List<Tag> tags = new ArrayList<Tag>();
    private final List<Resource> resources = new ArrayList<Resource>();
}
public class Resource {
    private String lang;
    private String path;
    private String mimeType;
    private LocalDateTime lastModified;
}
public class Tag {
    private String namespace;
    private String name;
}

第一个问题，即使阅读了这里的很多帖子，我仍然不完全理解。如何将 JSON 中的资源数组反序列化到我的资源描述列表中？

第二个也是最复杂的问题。以“tag_”为前缀的 JSON 属性需要转换为 Tag 类，而属性名称代表命名空间，值(单个或数组)代表名称。因此，如果模式是“namespace:name”，第一个 ResourceDescription 将具有以下标签:

• tag_pagetype:默认
• tag_bookingcenter:bc_ch
• tag_bookingcenter:bc_de

第三，“lastmodified”应该从 Joda-Time 转换为 DateTime。

这是否可以通过数据绑定(bind)实现，还是应该坚持使用树模型？

Answer 1

How do I deserialize this array of Resources from the JSON into my List of the ResourceDescription?

您必须创建额外的root类，其中包含resourcedescriptions属性。例如:

class Root {

    private List<ResourceDescription> resourcedescriptions;

    public List<ResourceDescription> getResourcedescriptions() {
        return resourcedescriptions;
    }

    public void setResourcedescriptions(List<ResourceDescription> resourcedescriptions) {
        this.resourcedescriptions = resourcedescriptions;
    }

    @Override
    public String toString() {
        return String.valueOf(resourcedescriptions);
    }
}

The JSON properties prefixed with "tag_" need to be transformed into the Tag class, whereas the the property name represents the namespace and the value (single or array) represent the name.

您可以使用@JsonAnySetter注释来处理这种情况。您必须向 ResourceDescription 类添加新方法，如下所示:

@JsonAnySetter
public void setAnyValues(String propertyName, Object value) {
    if (propertyName.startsWith("tag_")) {
        if (value instanceof String) {
            tags.add(new Tag(propertyName, value.toString()));
        } else if (value instanceof List) {
            List<?> values = (List<?>) value;
            for (Object v : values) {
                tags.add(new Tag(propertyName, v.toString()));
            }
        }
        // throw exception?
    } else {
        // handle another unknown properties
    }
}

Third the "lastmodified" should be transformed into DateTime from Joda-Time.

您可以通过添加 jackson-datatype-joda 来处理 JodaTime 类型图书馆。添加后，您可以注册 JodaModule 模块。

mapper.registerModule(new JodaModule());

另一个问题是您的 JSON 包含使用小写字母编写的属性，但您的 POJO 属性是使用驼峰式大小写编写的。您可以更改 JSON 或 POJO 或使用 @JsonProperty("property-name-from-JSON") 注解或实现您自己的命名策略。例如:

mapper.setPropertyNamingStrategy(new PropertyNamingStrategy.PropertyNamingStrategyBase() {
    @Override
    public String translate(String propertyName) {
        return propertyName.toLowerCase();
    }
});

如何反序列化 JSON 的完整 Java 示例:

import java.util.ArrayList;
import java.util.List;

import org.joda.time.LocalDateTime;

import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.PropertyNamingStrategy;
import com.fasterxml.jackson.datatype.joda.JodaModule;

public class JacksonProgram {

    public static void main(String[] args) throws Exception {
        String json = "{ ... }";
        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(new JodaModule());
        mapper.setPropertyNamingStrategy(new PropertyNamingStrategy.PropertyNamingStrategyBase() {
            @Override
            public String translate(String propertyName) {
                return propertyName.toLowerCase();
            }
        });

        System.out.println(mapper.readValue(json, Root.class));
    }
}

class Root {

    private List<ResourceDescription> resourcedescriptions;

    public List<ResourceDescription> getResourcedescriptions() {
        return resourcedescriptions;
    }

    public void setResourcedescriptions(List<ResourceDescription> resourcedescriptions) {
        this.resourcedescriptions = resourcedescriptions;
    }

    @Override
    public String toString() {
        return String.valueOf(resourcedescriptions);
    }
}

class ResourceDescription {

    private String path;
    private LocalDateTime lastModified;
    private String chartConfig;
    private final List<Tag> tags = new ArrayList<Tag>();
    private final List<Resource> resources = new ArrayList<Resource>();

    @JsonAnySetter
    public void setAnyValues(String propertyName, Object value) {
        if (propertyName.startsWith("tag_")) {
            if (value instanceof String) {
                tags.add(new Tag(propertyName, value.toString()));
            } else if (value instanceof List) {
                List<?> values = (List<?>) value;
                for (Object v : values) {
                    tags.add(new Tag(propertyName, v.toString()));
                }
            }
            // throw exception?
        } else {
            // handle another unknown properties
        }
    }

    public String getPath() {
        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }

    public LocalDateTime getLastModified() {
        return lastModified;
    }

    public void setLastModified(LocalDateTime lastModified) {
        this.lastModified = lastModified;
    }

    public String getChartConfig() {
        return chartConfig;
    }

    public void setChartConfig(String chartConfig) {
        this.chartConfig = chartConfig;
    }

    public List<Tag> getTags() {
        return tags;
    }

    public List<Resource> getResources() {
        return resources;
    }

    @Override
    public String toString() {
        return "ResourceDescription [path=" + path + ", lastModified=" + lastModified
                + ", chartConfig=" + chartConfig + ", tags=" + tags + ", resources=" + resources
                + "]";
    }
}

class Resource {

    private String lang;
    private String path;
    private String mimeType;
    private LocalDateTime lastModified;

    public String getLang() {
        return lang;
    }

    public void setLang(String lang) {
        this.lang = lang;
    }

    public String getPath() {
        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }

    public String getMimeType() {
        return mimeType;
    }

    public void setMimeType(String mimeType) {
        this.mimeType = mimeType;
    }

    public LocalDateTime getLastModified() {
        return lastModified;
    }

    public void setLastModified(LocalDateTime lastModified) {
        this.lastModified = lastModified;
    }

    @Override
    public String toString() {
        return "Resource [lang=" + lang + ", path=" + path + ", mimeType=" + mimeType
                + ", lastModified=" + lastModified + "]";
    }
}

class Tag {

    private String namespace;
    private String name;

    public Tag() {
    }

    public Tag(String namespace, String name) {
        this.namespace = namespace;
        this.name = name;
    }

    public String getNamespace() {
        return namespace;
    }

    public void setNamespace(String namespace) {
        this.namespace = namespace;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Tag [namespace=" + namespace + ", name=" + name + "]";
    }
}

以上程序打印:

[ResourceDescription [path=somePath, lastModified=2014-05-12T17:07:04.208, chartConfig=null, tags=[Tag [namespace=tag_pagetype, name=default], Tag [namespace=tag_bookingcenter, name=bc_ch], Tag [namespace=tag_bookingcenter, name=bc_de]], resources=[Resource [lang=de, path=somePathDe.html, mimeType=text/html, lastModified=2014-05-02T10:47:22.914], Resource [lang=en, path=somePathEn.html, mimeType=text/html, lastModified=2014-05-12T17:07:04.208]]], ResourceDescription [path=someOtherPath, lastModified=2014-05-12T17:07:04.208, chartConfig=null, tags=[Tag [namespace=tag_pagetype, name=special], Tag [namespace=tag_bookingcenter, name=bc_ch]], resources=[Resource [lang=de, path=someOtherPathDe.html, mimeType=text/html, lastModified=2014-05-02T10:47:22.914], Resource [lang=en, path=someOtherPathEn.html, mimeType=text/html, lastModified=2014-05-12T17:07:04.208]]]]