我想知道是否有可用的Java API可以将一个POJO对象转换为JSON对象,反之亦然。
假设你有一个这样简单的Java类:
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 );
}
}
这里有另一个例子,使用Jackson进行操作: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>
以下是最新版本的链接:
如果您了解Jackson 2,则在mkyong.com上有一个很好的教程,介绍如何将Java对象与JSON相互转换。以下代码片段摘自该教程。
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,使用 readValue(...)
方法:
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);
Jackson 2 依赖:
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.6.3</version>
</dependency>
请前往上方给出的链接获取完整教程。
我们还可以在pom文件中使用下面提供的依赖和插件 - 我使用maven。通过使用这些,您可以根据您的JSON模式生成POJO,然后使用下面给出的代码来通过指定为gson.toJson(Object src)参数的src对象填充请求JSON对象或反之亦然。请查看以下代码:
Gson gson = new GsonBuilder().create();
String payloadStr = gson.toJson(data.getMerchant().getStakeholder_list());
Gson gson2 = new Gson();
Error expectederr = gson2.fromJson(payloadStr, Error.class);
同时还需要 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>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.4</version>
</dependency>
ObjectMapper mapper = new ObjectMapper();
mapper.enable(SerializationFeature.INDENT_OUTPUT);
String json = mapper.writeValueAsString(pojo);
{
"type":"object",
"properties": {
"dataOne": {
"type": "string"
},
"dataTwo": {
"type": "integer"
},
"dataThree": {
"type": "boolean"
}
}
}
然后要转换为POJO,您需要按照以下样式声明一些类:
==================================
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。请参考此处。
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。