如何将POJO转换为JSON,反之亦然?

2021/01/17 14:11 · java ·  · 0评论

我想知道是否有任何Java API可用于将POJO对象转换为JSON对象,反之亦然。

看看https://www.json.org

[编辑]想象一下,您有一个简单的Java类,如下所示:

public class Person {

    private String name;
    private Integer age;

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

    public Integer getAge() { return this.age; }
    public void setAge( Integer age ) { this.age = age; }

}

因此,将其转换为JSon对象非常简单。像这样:

import org.json.JSONObject;

public class JsonTest {

    public static void main( String[] args ) {
        Person person = new Person();
        person.setName( "Person Name" );
        person.setAge( 333 );

        JSONObject jsonObj = new JSONObject( person );
        System.out.println( jsonObj );
    }

}

希望能帮助到你。

[编辑]这里还有其他示例,在这种情况下使用杰克逊:https : //brunozambiazi.wordpress.com/2015/08/15/working-with-json-in-java/

Maven:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.6.1</version>
</dependency>

以及一个链接(在下面)以找到最新/最新版本:

https://search.maven.org/classic/#search%7Cga%7C1%7Cg%3A%22com.fasterxml.jackson.core%22%20AND%20a%3A%22jackson-databind%22

我们还可以在pom文件中利用以下给定的依赖关系和插件-我利用了maven。借助这些,您可以根据JSON Schema生成POJO,然后利用下面给出的代码通过指定为gson.toJson(Object src)参数的src对象填充请求JSON对象,反之亦然。看下面的代码:

Gson gson = new GsonBuilder().create();
String payloadStr = gson.toJson(data.getMerchant().getStakeholder_list());

Gson gson2 = new Gson();
Error expectederr = gson2.fromJson(payloadStr, Error.class);

和Maven设置:

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>1.7.1</version>
</dependency>

<plugin>
    <groupId>com.googlecode.jsonschema2pojo</groupId>
    <artifactId>jsonschema2pojo-maven-plugin</artifactId>
    <version>0.3.7</version>
    <configuration>
        <sourceDirectory>${basedir}/src/main/resources/schema</sourceDirectory>
        <targetPackage>com.example.types</targetPackage>
    </configuration>
    <executions>
        <execution>
            <phase>generate-sources</phase>
            <goals>
                <goal>generate</goal>
            </goals>
        </execution>
    </executions>
</plugin>

如果您了解Jackson 2mkyong.com有一个很棒的教程,介绍如何将Java对象转换为JSON,反之亦然。以下代码段摘自该教程。

将Java对象转换为JSON writeValue(...)

ObjectMapper mapper = new ObjectMapper();
Staff obj = new Staff();

//Object to JSON in file
mapper.writeValue(new File("c:\\file.json"), obj);

//Object to JSON in String
String jsonInString = mapper.writeValueAsString(obj);

将JSON转换为Java对象readValue(...)

ObjectMapper mapper = new ObjectMapper();
String jsonInString = "{'name' : 'mkyong'}";

//JSON from file to Object
Staff obj = mapper.readValue(new File("c:\\file.json"), Staff.class);

//JSON from URL to Object
Staff obj = mapper.readValue(new URL("http://mkyong.com/api/staff.json"), Staff.class);

//JSON from String to Object
Staff obj = mapper.readValue(jsonInString, Staff.class);

杰克逊2依赖:

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.6.3</version>
</dependency>

有关完整的教程,请转到上面给出的链接。

您可以使用杰克逊API进行转换

<dependency>
  <groupId>com.fasterxml.jackson.core</groupId>
  <artifactId>jackson-databind</artifactId>
  <version>2.9.4</version>
</dependency>

在您的POM中添加上述Maven依赖项,在您的主要方法中创建ObjectMapper

ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);

稍后我们需要将我们的POJO类添加到映射器

String json = mapper.writeValueAsString(pojo);

采取以下参考将JSON转换为POJO,反之亦然

假设您的JSON模式如下所示:

{
  "type":"object",
  "properties": {
    "dataOne": {
      "type": "string"
    },
    "dataTwo": {
      "type": "integer"
    },
    "dataThree": {
      "type": "boolean"
    }
  }
}

然后隐匿到POJO中,您需要清除一些类,如以下样式中所述:

==================================
package ;
public class DataOne
{
    private String type;

    public void setType(String type){
        this.type = type;
    }
    public String getType(){
        return this.type;
    }
}

==================================
package ;
public class DataTwo
{
    private String type;

    public void setType(String type){
        this.type = type;
    }
    public String getType(){
        return this.type;
    }
}

==================================
package ;
public class DataThree
{
    private String type;

    public void setType(String type){
        this.type = type;
    }
    public String getType(){
        return this.type;
    }
}

==================================
package ;
public class Properties
{
    private DataOne dataOne;

    private DataTwo dataTwo;

    private DataThree dataThree;

    public void setDataOne(DataOne dataOne){
        this.dataOne = dataOne;
    }
    public DataOne getDataOne(){
        return this.dataOne;
    }
    public void setDataTwo(DataTwo dataTwo){
        this.dataTwo = dataTwo;
    }
    public DataTwo getDataTwo(){
        return this.dataTwo;
    }
    public void setDataThree(DataThree dataThree){
        this.dataThree = dataThree;
    }
    public DataThree getDataThree(){
        return this.dataThree;
    }
}

==================================
package ;
public class Root
{
    private String type;

    private Properties properties;

    public void setType(String type){
        this.type = type;
    }
    public String getType(){
        return this.type;
    }
    public void setProperties(Properties properties){
        this.properties = properties;
    }
    public Properties getProperties(){
        return this.properties;
    }
}

使用GSON将POJO转换为JSONObject。请参考这里。

要将JSONObject转换为POJO,只需在POJO中调用setter方法并直接从JSONObject分配值即可。

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