1.说明

jsonschema2pojo工具可以从JSON Schema(或示例JSON文件)生成Java类型，
并且可以配置生成Jackson 1.x,Jackson 2.x, Moshi 1.x或者Gson库的注解。
支持将jsonschema2pojo作为Maven插件、Ant任务、命令行工具、
Gradle插件或嵌入到Java应用程序中。
本文仅介绍Maven插件使用方式。
另外该工具还提供了在线版本,
可以在网站上直接使用：jsonschema2pojo online

2.创建Maven工程

Eclipse -> File -> New -> Other... -> Maven -> Maven Project
创建一个简单Maven工程，
pom.xml如下：

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>edu.yuwen.util</groupId><artifactId>json-file</artifactId><version>0.0.1-SNAPSHOT</version></parent><artifactId>generate-jsonschema2pojo</artifactId><description>jsonschema2pojo generates Java types from JSON Schema (or example JSON)</description>
</project>

3.引入Maven插件

Maven方式生成Java类需要jsonschema2pojo-maven-plugin，
在pom.xml引入这个插件：

<build><plugins><plugin><groupId>org.jsonschema2pojo</groupId><artifactId>jsonschema2pojo-maven-plugin</artifactId><version>1.0.2</version><configuration><sourceDirectory>${basedir}/src/main/resources/schema</sourceDirectory><targetPackage>com.example.types</targetPackage></configuration><executions><execution><goals><goal>generate</goal></goals></execution></executions></plugin></plugins>
</build>

里面的配置项指定了JSON schema文件的目录，
以及生成的Java类的包路径。

4.新建JSON Schema

在src/main/resources/schema目录下
新建JSON Schema文件address.schema.json:

{"$id": "https://example.com/address.schema.json","$schema": "http://json-schema.org/draft-07/schema#","description": "An address similar to http://microformats.org/wiki/h-card","type": "object","properties": {"post-office-box": {"type": "string"},"extended-address": {"type": "string"},"street-address": {"type": "string"},"locality": {"type": "string"},"region": {"type": "string"},"postal-code": {"type": "string"},"country-name": {"type": "string"}},"required": [ "locality", "region", "country-name" ],"dependencies": {"post-office-box": [ "street-address" ],"extended-address": [ "street-address" ]}
}

5.运行Maven插件

运行Maven命令，
执行插件功能：
mvn generate-sources
或者
mvn package
Maven执行成功后，
会生成target/generated-sources/jsonschema2pojo/com/example/types/Address.java类。
推荐使用mvn generate-sources，
这样生成的target目录更干净些。

6.查看Address.java

package com.example.types;import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;/*** An address similar to http://microformats.org/wiki/h-card* */
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({"post-office-box","extended-address","street-address","locality","region","postal-code","country-name"
})
public class AddressSchema {@JsonProperty("post-office-box")private String postOfficeBox;@JsonProperty("extended-address")private String extendedAddress;@JsonProperty("street-address")private String streetAddress;/*** * (Required)* */@JsonProperty("locality")private String locality;/*** * (Required)* */@JsonProperty("region")private String region;@JsonProperty("postal-code")private String postalCode;/*** * (Required)* */@JsonProperty("country-name")private String countryName;@JsonIgnoreprivate Map<String, Object> additionalProperties = new HashMap<String, Object>();@JsonProperty("post-office-box")public String getPostOfficeBox() {return postOfficeBox;}@JsonProperty("post-office-box")public void setPostOfficeBox(String postOfficeBox) {this.postOfficeBox = postOfficeBox;}@JsonProperty("extended-address")public String getExtendedAddress() {return extendedAddress;}@JsonProperty("extended-address")public void setExtendedAddress(String extendedAddress) {this.extendedAddress = extendedAddress;}@JsonProperty("street-address")public String getStreetAddress() {return streetAddress;}@JsonProperty("street-address")public void setStreetAddress(String streetAddress) {this.streetAddress = streetAddress;}/*** * (Required)* */@JsonProperty("locality")public String getLocality() {return locality;}/*** * (Required)* */@JsonProperty("locality")public void setLocality(String locality) {this.locality = locality;}/*** * (Required)* */@JsonProperty("region")public String getRegion() {return region;}/*** * (Required)* */@JsonProperty("region")public void setRegion(String region) {this.region = region;}@JsonProperty("postal-code")public String getPostalCode() {return postalCode;}@JsonProperty("postal-code")public void setPostalCode(String postalCode) {this.postalCode = postalCode;}/*** * (Required)* */@JsonProperty("country-name")public String getCountryName() {return countryName;}/*** * (Required)* */@JsonProperty("country-name")public void setCountryName(String countryName) {this.countryName = countryName;}@JsonAnyGetterpublic Map<String, Object> getAdditionalProperties() {return this.additionalProperties;}@JsonAnySetterpublic void setAdditionalProperty(String name, Object value) {this.additionalProperties.put(name, value);}@Overridepublic String toString() {StringBuilder sb = new StringBuilder();sb.append(AddressSchema.class.getName()).append('@').append(Integer.toHexString(System.identityHashCode(this))).append('[');sb.append("postOfficeBox");sb.append('=');sb.append(((this.postOfficeBox == null)?"<null>":this.postOfficeBox));sb.append(',');sb.append("extendedAddress");sb.append('=');sb.append(((this.extendedAddress == null)?"<null>":this.extendedAddress));sb.append(',');sb.append("streetAddress");sb.append('=');sb.append(((this.streetAddress == null)?"<null>":this.streetAddress));sb.append(',');sb.append("locality");sb.append('=');sb.append(((this.locality == null)?"<null>":this.locality));sb.append(',');sb.append("region");sb.append('=');sb.append(((this.region == null)?"<null>":this.region));sb.append(',');sb.append("postalCode");sb.append('=');sb.append(((this.postalCode == null)?"<null>":this.postalCode));sb.append(',');sb.append("countryName");sb.append('=');sb.append(((this.countryName == null)?"<null>":this.countryName));sb.append(',');sb.append("additionalProperties");sb.append('=');sb.append(((this.additionalProperties == null)?"<null>":this.additionalProperties));sb.append(',');if (sb.charAt((sb.length()- 1)) == ',') {sb.setCharAt((sb.length()- 1), ']');} else {sb.append(']');}return sb.toString();}@Overridepublic int hashCode() {int result = 1;result = ((result* 31)+((this.postOfficeBox == null)? 0 :this.postOfficeBox.hashCode()));result = ((result* 31)+((this.streetAddress == null)? 0 :this.streetAddress.hashCode()));result = ((result* 31)+((this.postalCode == null)? 0 :this.postalCode.hashCode()));result = ((result* 31)+((this.locality == null)? 0 :this.locality.hashCode()));result = ((result* 31)+((this.countryName == null)? 0 :this.countryName.hashCode()));result = ((result* 31)+((this.additionalProperties == null)? 0 :this.additionalProperties.hashCode()));result = ((result* 31)+((this.extendedAddress == null)? 0 :this.extendedAddress.hashCode()));result = ((result* 31)+((this.region == null)? 0 :this.region.hashCode()));return result;}@Overridepublic boolean equals(Object other) {if (other == this) {return true;}if ((other instanceof AddressSchema) == false) {return false;}AddressSchema rhs = ((AddressSchema) other);return (((((((((this.postOfficeBox == rhs.postOfficeBox)||((this.postOfficeBox!= null)&&this.postOfficeBox.equals(rhs.postOfficeBox)))&&((this.streetAddress == rhs.streetAddress)||((this.streetAddress!= null)&&this.streetAddress.equals(rhs.streetAddress))))&&((this.postalCode == rhs.postalCode)||((this.postalCode!= null)&&this.postalCode.equals(rhs.postalCode))))&&((this.locality == rhs.locality)||((this.locality!= null)&&this.locality.equals(rhs.locality))))&&((this.countryName == rhs.countryName)||((this.countryName!= null)&&this.countryName.equals(rhs.countryName))))&&((this.additionalProperties == rhs.additionalProperties)||((this.additionalProperties!= null)&&this.additionalProperties.equals(rhs.additionalProperties))))&&((this.extendedAddress == rhs.extendedAddress)||((this.extendedAddress!= null)&&this.extendedAddress.equals(rhs.extendedAddress))))&&((this.region == rhs.region)||((this.region!= null)&&this.region.equals(rhs.region))));}}

7.引入插件依赖

当把Address.java放到工程的src/main/java目录下时，
Java编译会报错，
这是因为生成的类型依赖于Commons Lang的equals、hashCode和toString。
一些模式结构也会以Jackson注释的形式产生解析器提示。
需要在pom.xml中添加必要的依赖：

<dependencies><dependency><groupId>commons-lang</groupId><artifactId>commons-lang</artifactId><version>2.4</version></dependency><dependency><groupId>com.fasterxml.jackson.core</groupId><artifactId>jackson-databind</artifactId><version>2.5.4</version></dependency>
</dependencies>

8.新建JSON文件

上面演示了从JSON Schema生成Java类，
下面演示从JSON文件生成Java类，
首先在src\main\resources\json目录下，
新建一个JOSN文件person.json：

{"name":"bob","age":33
}

9.修改插件配置

主要是指定了sourceType和sourceDirectory，
指定了源文件的格式是json和所在目录。

<build><plugins><plugin><groupId>org.jsonschema2pojo</groupId><artifactId>jsonschema2pojo-maven-plugin</artifactId><version>1.0.2</version><configuration><sourceType>json</sourceType><sourceDirectory>${basedir}/src/main/resources/json</sourceDirectory><outputDirectory>${basedir}/src/main/java</outputDirectory><targetPackage>com.example.types</targetPackage><addCompileSourceRoot>true</addCompileSourceRoot><annotationStyle>jackson2</annotationStyle></configuration><executions><execution><goals><goal>generate</goal></goals></execution></executions></plugin></plugins>
</build>

10.生成Person.java类

mvn generate-sources执行成功后，
会生成src/main/java/com/example/types/Person.java：

package com.example.types;import java.util.HashMap;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({"name","age"
})
public class Person {@JsonProperty("name")private String name;@JsonProperty("age")private Integer age;@JsonIgnoreprivate Map<String, Object> additionalProperties = new HashMap<String, Object>();@JsonProperty("name")public String getName() {return name;}@JsonProperty("name")public void setName(String name) {this.name = name;}@JsonProperty("age")public Integer getAge() {return age;}@JsonProperty("age")public void setAge(Integer age) {this.age = age;}@JsonAnyGetterpublic Map<String, Object> getAdditionalProperties() {return this.additionalProperties;}@JsonAnySetterpublic void setAdditionalProperty(String name, Object value) {this.additionalProperties.put(name, value);}@Overridepublic String toString() {StringBuilder sb = new StringBuilder();sb.append(Person.class.getName()).append('@').append(Integer.toHexString(System.identityHashCode(this))).append('[');sb.append("name");sb.append('=');sb.append(((this.name == null)?"<null>":this.name));sb.append(',');sb.append("age");sb.append('=');sb.append(((this.age == null)?"<null>":this.age));sb.append(',');sb.append("additionalProperties");sb.append('=');sb.append(((this.additionalProperties == null)?"<null>":this.additionalProperties));sb.append(',');if (sb.charAt((sb.length()- 1)) == ',') {sb.setCharAt((sb.length()- 1), ']');} else {sb.append(']');}return sb.toString();}@Overridepublic int hashCode() {int result = 1;result = ((result* 31)+((this.name == null)? 0 :this.name.hashCode()));result = ((result* 31)+((this.additionalProperties == null)? 0 :this.additionalProperties.hashCode()));result = ((result* 31)+((this.age == null)? 0 :this.age.hashCode()));return result;}@Overridepublic boolean equals(Object other) {if (other == this) {return true;}if ((other instanceof Person) == false) {return false;}Person rhs = ((Person) other);return ((((this.name == rhs.name)||((this.name!= null)&&this.name.equals(rhs.name)))&&((this.additionalProperties == rhs.additionalProperties)||((this.additionalProperties!= null)&&this.additionalProperties.equals(rhs.additionalProperties))))&&((this.age == rhs.age)||((this.age!= null)&&this.age.equals(rhs.age))));}
}

11.插件配置项说明

1. sourceType:两个可选值，JSON Schema或者JSON文件，默认为JSON Schema。
2. sourceDirectory:源文件所在的目录，会将该目录下所有文件进行转换，不支持指定单个文件，如果不想全部转换，可以添加一个excludes节点。
3. outputDirectory:生成Java Pojo类的(根)目录，生成Java类的目录为此目录+包目录，默认值为target/generated-sources/jsonschema2pojo。
4. targetPackage:生成的Java pojo类的包路径。
5. addCompileSourceRoot:是否将输出目录作为项目的源码根目录。
6. annotationStyle:生成的(字段)注解样式，五个可选值：jackson1、jackson2、gson、moshi1和none，默认是jackson2，如果fastjson等工具不支持的，需要设置为none。

更多配置项的使用请参考：jsonschema2pojo-maven-plugin Optional Parameters

12.参考文章

使用maven根据JSON文件自动生成Java POJO类(Java Bean)源文件jsonschema2pojo github