我在代码中使用 jsonschema2pojo 时遇到问题。所以，我使用 jsonschema2pojo 生成器（http://www.jsonschema2pojo.org/）从这个 URL 生成 POJO：http ://store.steampowered.com/api/appdetails/?appids=10
最后，我在一个包“模型”中创建了所有这些类。然后在我尝试使用它从链接中读取 json 但我收到异常：
Exception in thread "main" java.lang.NullPointerException
at controller.View.main(View.java:26)
我不明白为什么。这是代码我该怎么做：
public class View {
private static String urlStr = "http://store.steampowered.com/api/appdetails/?appids=10";
public static void main(String[] args) {
ObjectMapper objectMapper = new ObjectMapper();
try {
Game game = objectMapper.readValue(new URL(urlStr), Game.class);
System.out.println(game.getData().getName());
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (JsonParseException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
Game.class 是我在生成器中设置为“类名”的 finall 类。
怎么了？如何从此链接获取所有这些数据？
在 Maven 中，我像这样配置它：
<plugin>
<groupId>org.jsonschema2pojo</groupId>
<artifactId>jsonschema2pojo-maven-plugin</artifactId>
<version>0.4.18</version>
<configuration>
<sourceType>jsonschema</sourceType>
<outputEncoding>${project.build.sourceEncoding}</outputEncoding>
<outputDirectory>${project.build.directory}/generated-sources</outputDirectory>
<annotationStyle>jackson2</annotationStyle>
<generateBuilders>true</generateBuilders>
<initializeCollections>true</initializeCollections>
</configuration>
<executions>
<execution>
<id>generate-game</id>
<goals>
<goal>generate</goal>
</goals>
<configuration>
<targetPackage>model.game</targetPackage>
<sourceDirectory>${basedir}/src/main/resources/schema/game</sourceDirectory>
</configuration>
</execution>
</executions>
</plugin>
正如我所说，所有类都在 src/main/java 和包“模型”中，我的模式在文件“游戏”中的 sr/main/resources/schema/
我的架构看起来像：
{
"type": "object",
"required":false,
"javaType":"model.Game",
"properties": {
"10": {
"id": "10",
"type": "object",
"properties": {
"success": {
"id": "success",
"type": "boolean"
},
"data": {
"id": "data",
"type": "object",
"properties": {
"type": {
"id": "type",
"type": "string"
},
"name": {
"id": "name",
"type": "string"
},
"steam_appid": {
"id": "steam_appid",
"type": "integer"
},
"required_age": {
"id": "required_age",
"type": "integer"
},
"is_free": {
"id": "is_free",
"type": "boolean"
},
"detailed_description": {
"id": "detailed_description",
"type": "string"
},
"about_the_game": {
"id": "about_the_game",
"type": "string"
},
"supported_languages": {
"id": "supported_languages",
"type": "string"
},
"header_image": {
"id": "header_image",
"type": "string"
},
"website": {
"id": "website",
"type": "null"
},
"pc_requirements": {
"id": "pc_requirements",
"type": "object",
"properties": {
"minimum": {
"id": "minimum",
"type": "string"
}
}
},
"mac_requirements": {
"id": "mac_requirements",
"type": "object",
"properties": {
"minimum": {
"id": "minimum",
"type": "string"
}
}
},
"linux_requirements": {
"id": "linux_requirements",
"type": "object",
"properties": {
"minimum": {
"id": "minimum",
"type": "string"
}
}
},
"developers": {
"id": "developers",
"type": "array",
"items": {
"id": "0",
"type": "string"
}
},
"publishers": {
"id": "publishers",
"type": "array",
"items": {
"id": "0",
"type": "string"
}
},
"price_overview": {
"id": "price_overview",
"type": "object",
"properties": {
"currency": {
"id": "currency",
"type": "string"
},
"initial": {
"id": "initial",
"type": "integer"
},
"final": {
"id": "final",
"type": "integer"
},
"discount_percent": {
"id": "discount_percent",
"type": "integer"
}
}
},
"packages": {
"id": "packages",
"type": "array",
"items": [
{
"id": "0",
"type": "string"
},
{
"id": "1",
"type": "integer"
},
{
"id": "2",
"type": "integer"
},
{
"id": "3",
"type": "integer"
}
]
},
"package_groups": {
"id": "package_groups",
"type": "array",
"items": {
"id": "0",
"type": "object",
"properties": {
"name": {
"id": "name",
"type": "string"
},
"title": {
"id": "title",
"type": "string"
},
"description": {
"id": "description",
"type": "string"
},
"selection_text": {
"id": "selection_text",
"type": "string"
},
"save_text": {
"id": "save_text",
"type": "string"
},
"display_type": {
"id": "display_type",
"type": "integer"
},
"is_recurring_subscription": {
"id": "is_recurring_subscription",
"type": "string"
},
"subs": {
"id": "subs",
"type": "array",
"items": [
{
"id": "0",
"type": "object",
"properties": {
"packageid": {
"id": "packageid",
"type": "string"
},
"percent_savings_text": {
"id": "percent_savings_text",
"type": "string"
},
"percent_savings": {
"id": "percent_savings",
"type": "integer"
},
"option_text": {
"id": "option_text",
"type": "string"
},
"option_description": {
"id": "option_description",
"type": "string"
},
"can_get_free_license": {
"id": "can_get_free_license",
"type": "string"
},
"is_free_license": {
"id": "is_free_license",
"type": "boolean"
},
"price_in_cents_with_discount": {
"id": "price_in_cents_with_discount",
"type": "integer"
}
}
},
{
"id": "1",
"type": "object",
"properties": {
"packageid": {
"id": "packageid",
"type": "integer"
},
"percent_savings_text": {
"id": "percent_savings_text",
"type": "string"
},
"percent_savings": {
"id": "percent_savings",
"type": "integer"
},
"option_text": {
"id": "option_text",
"type": "string"
},
"option_description": {
"id": "option_description",
"type": "string"
},
"can_get_free_license": {
"id": "can_get_free_license",
"type": "string"
},
"is_free_license": {
"id": "is_free_license",
"type": "boolean"
},
"price_in_cents_with_discount": {
"id": "price_in_cents_with_discount",
"type": "integer"
}
}
},
{
"id": "2",
"type": "object",
"properties": {
"packageid": {
"id": "packageid",
"type": "integer"
},
"percent_savings_text": {
"id": "percent_savings_text",
"type": "string"
},
"percent_savings": {
"id": "percent_savings",
"type": "integer"
},
"option_text": {
"id": "option_text",
"type": "string"
},
"option_description": {
"id": "option_description",
"type": "string"
},
"can_get_free_license": {
"id": "can_get_free_license",
"type": "string"
},
"is_free_license": {
"id": "is_free_license",
"type": "boolean"
},
"price_in_cents_with_discount": {
"id": "price_in_cents_with_discount",
"type": "integer"
}
}
},
{
"id": "3",
"type": "object",
"properties": {
"packageid": {
"id": "packageid",
"type": "integer"
},
"percent_savings_text": {
"id": "percent_savings_text",
"type": "string"
},
"percent_savings": {
"id": "percent_savings",
"type": "integer"
},
"option_text": {
"id": "option_text",
"type": "string"
},
"option_description": {
"id": "option_description",
"type": "string"
},
"can_get_free_license": {
"id": "can_get_free_license",
"type": "string"
},
"is_free_license": {
"id": "is_free_license",
"type": "boolean"
},
"price_in_cents_with_discount": {
"id": "price_in_cents_with_discount",
"type": "integer"
}
}
}
]
}
}
}
},
"platforms": {
"id": "platforms",
"type": "object",
"properties": {
"windows": {
"id": "windows",
"type": "boolean"
},
"mac": {
"id": "mac",
"type": "boolean"
},
"linux": {
"id": "linux",
"type": "boolean"
}
}
},
"metacritic": {
"id": "metacritic",
"type": "object",
"properties": {
"score": {
"id": "score",
"type": "integer"
},
"url": {
"id": "url",
"type": "string"
}
}
},
"categories": {
"id": "categories",
"type": "array",
"items": [
{
"id": "0",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"description": {
"id": "description",
"type": "string"
}
}
},
{
"id": "1",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"description": {
"id": "description",
"type": "string"
}
}
}
]
},
"genres": {
"id": "genres",
"type": "array",
"items": {
"id": "0",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "string"
},
"description": {
"id": "description",
"type": "string"
}
}
}
},
"screenshots": {
"id": "screenshots",
"type": "array",
"items": [
{
"id": "0",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "1",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "2",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "3",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "4",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "5",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "6",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "7",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "8",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "9",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "10",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "11",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
},
{
"id": "12",
"type": "object",
"properties": {
"id": {
"id": "id",
"type": "integer"
},
"path_thumbnail": {
"id": "path_thumbnail",
"type": "string"
},
"path_full": {
"id": "path_full",
"type": "string"
}
}
}
]
},
"recommendations": {
"id": "recommendations",
"type": "object",
"properties": {
"total": {
"id": "total",
"type": "integer"
}
}
},
"achievements": {
"id": "achievements",
"type": "object",
"properties": {
"total": {
"id": "total",
"type": "integer"
}
}
},
"release_date": {
"id": "release_date",
"type": "object",
"properties": {
"coming_soon": {
"id": "coming_soon",
"type": "boolean"
},
"date": {
"id": "date",
"type": "string"
}
}
},
"support_info": {
"id": "support_info",
"type": "object",
"properties": {
"url": {
"id": "url",
"type": "string"
},
"email": {
"id": "email",
"type": "string"
}
}
},
"background": {
"id": "background",
"type": "string"
}
}
}
},
"required": [
"success",
"data",
"id",
"path_thumbnail",
"path_full"
]
}
},
"required": [
"10"
]
}
有了这个配置，我可以使用这一行而不是在 System.out.println 之前读取所有数据：
System.out.println( objectMapper.writeValueAsString( game ) );
现在我可以看到完整的 json 字符串，但是如何使用 'game.getData().getName()' 等读取它？