通过Jackson实现Java对象和json字符串的相互转换

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：



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.code
4000
haus.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



将json字符串转换为java对象



将list集合转换为json字符串



将json字符串转换为list集合



将映射集合（Map）转换为json字符串



将json字符串转换为映射集合对象