通过Jackson实现Java对象和json字符串的相互转换

我不是女神ヾ 2022-06-07 07:12 286阅读 0赞

**通过Jackson实现Java对象和json字符串的相互转换**

下面的案例使用单元测试（junit）方式进行了测试，所以在测试中需要配置junit环境，本人使用的eclipse开发工具，eclipse自带junit测试环境但需要配置，其它的开发工具则需要导入junit测试包。

注:junit测试时测试的方法名必须以test开始，并且在方法上面必须加 @Test

需要导入的Jackson包：

![Center][]

示例代码如下：

package cn.sz.hcq.test;
    
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.Iterator;
    import java.util.List;
    import java.util.Map;
    import java.util.Set;
    
    import org.apache.jasper.tagplugins.jstl.core.ForEach;
    import org.codehaus.jackson.JsonGenerationException;
    import org.codehaus.jackson.JsonParseException;
    import org.codehaus.jackson.map.JsonMappingException;
    import org.codehaus.jackson.map.ObjectMapper;
    import org.codehaus.jackson.type.JavaType;
    import org.codehaus.jackson.type.TypeReference;
    import org.junit.Test;
    
    import cn.sz.hcq.pojo.User;
    
    public class JacksonTest {
    	/**
    	 * 将java对象转换为json字符串
    	 * 
    	 * @throws IOException
    	 * @throws JsonMappingException
    	 * @throws JsonGenerationException
    	 */
    	@Test
    	public void testObjectToString() throws JsonGenerationException, JsonMappingException, IOException {
    		User u1 = new User();
    		u1.setId(1);
    		u1.setName("张三");
    		// 创建实现转换的对象
    		ObjectMapper mapper = new ObjectMapper();
    		// 将java对象转换为json字符串
    		String str = mapper.writeValueAsString(u1);
    		System.out.println("将java对象转换为json字符串:" + str);
    	}
    
    	/**
    	 * 将json字符串转换为Java对象
    	 * 
    	 * @throws IOException
    	 * @throws JsonMappingException
    	 * @throws JsonParseException
    	 */
    	@Test
    	public void testStringToObject() throws JsonParseException, JsonMappingException, IOException {
    		String str = "{\"id\":1,\"name\":\"张三\"}";
    
    		ObjectMapper mapper = new ObjectMapper();
    		// 将json字符串解析为一个Java对象
    		User u = mapper.readValue(str, User.class);
    		System.out.println("将json字符串转换为Java对象:" + u.toString());
    	}
    
    	/**
    	 * 将List对象转换为Json字符串
    	 * 
    	 * @throws JsonGenerationException
    	 * @throws JsonMappingException
    	 * @throws IOException
    	 */
    	@Test
    	public void testListToString() throws JsonGenerationException, JsonMappingException, IOException {
    
    		User u1 = new User();
    		u1.setId(1);
    		u1.setName("张三");
    
    		User u2 = new User();
    		u2.setId(2);
    		u2.setName("李四");
    
    		List<User> list = new ArrayList<>();
    		list.add(u1);
    		list.add(u2);
    
    		ObjectMapper oMapper = new ObjectMapper();
    		String str = oMapper.writeValueAsString(list);
    
    		System.out.println("将List对象转换为Json字符串:" + str);
    	}
    
    	/**
    	 * 将Json字符串转换为List对象
    	 * 
    	 * @throws IOException
    	 * @throws JsonMappingException
    	 * @throws JsonParseException
    	 */
    	@Test
    	public void testStringToList() throws JsonParseException, JsonMappingException, IOException {
    		String str = "[{\"id\":1,\"name\":\"张三\"},{\"id\":1,\"name\":\"李四\"}]";
    		ObjectMapper mapper = new ObjectMapper();
    		List<User> list = mapper.readValue(str, getCollectionType(List.class, User.class));
    		for (User u : list) {
    			System.out.println("将Json字符串转换为List对象:" + u);
    		}
    	}
    
    	public JavaType getCollectionType(Class<?> collectionClass, Class<?>... elementClasses) {
    		ObjectMapper mapper = new ObjectMapper();
    		return mapper.getTypeFactory().constructParametricType(collectionClass, elementClasses);
    	}
    
    	/**
    	 * 将Map对象转换为Json字符串
    	 * 
    	 * @throws JsonGenerationException
    	 * @throws JsonMappingException
    	 * @throws IOException
    	 */
    	@Test
    	public void testMapToString() throws JsonGenerationException, JsonMappingException, IOException {
    
    		User u1 = new User();
    		u1.setId(1);
    		u1.setName("张三");
    
    		User u2 = new User();
    		u2.setId(2);
    		u2.setName("李四");
    
    		Map<String, User> map = new HashMap<>();
    		map.put("u1", u1);
    		map.put("u2", u2);
    
    		ObjectMapper oMapper = new ObjectMapper();
    		String str = oMapper.writeValueAsString(map);
    
    		System.out.println("将Map对象转换为Json字符串:" + str);
    	}
    
    	/**
    	 * 将Json字符串转换为Map对象
    	 * 
    	 * @throws IOException
    	 * @throws JsonMappingException
    	 * @throws JsonParseException
    	 */
    	@Test
    	public void testStringToMap() throws JsonParseException, JsonMappingException, IOException {
    		String str = "{\"u1\":{\"id\":1,\"name\":\"张三\"},\"u2\":{\"id\":2,\"name\":\"李四\"}}";
    		ObjectMapper mapper = new ObjectMapper();
    		Map<String, User> map = mapper.readValue(str, new TypeReference<Map<String, User>>() {
    		});
    
    		Set<String> set = map.keySet();
    		Iterator<String> it = set.iterator();
    		while (it.hasNext()) {
    			String key = (String) it.next();
    			System.out.println(key + "," + map.get(key));
    		}
    
    	}
    
    }

**测试结果如下：**

将Java对象转换为json字符串

![Center 1][]

将json字符串转换为java对象

![Center 2][]

将list集合转换为json字符串

![Center 3][]

将json字符串转换为list集合

![Center 4][]

将映射集合（Map）转换为json字符串

![Center 5][]

将json字符串转换为映射集合对象

![Center 6][]

[Center]: /images/20220607/bbaf4e17f8c54ca685e29c04ea957445.png
[Center 1]: /images/20220607/7e8505c0a23d41d8a075cf03501813d0.png
[Center 2]: /images/20220607/1d260f241a8e426990c70fb717a34b21.png
[Center 3]: /images/20220607/89cce001f73c441ca1ee66c2eda5c69a.png
[Center 4]: /images/20220607/f2842689d2914efa96d27e0701cda8b2.png
[Center 5]: /images/20220607/3b73ad7911c3445491c350ad308029ce.png
[Center 6]: /images/20220607/f48d0d54041548e8b14ad40ace05e078.png