Jackson常用方法以及jacksonUtil工具类详解

前言：

项目中我们通常使用ajax返回json数据格式的形式进行前后端数据交互，所以会用到java数据json数据互相转化，通常我们的做法是在项目中创建一个工具类进行转化处理。

如下：

我的demo包含了项目中常用的jacksonUtil类，以及常用的JSON JAVA处理数据转化处理方法。

项目结构以及引用jar包如下，jar包中的junit是用于单元测试，与jackson及其相关的包无关。

每个部分我都加了注释，直接copy下来运行就可以查看具体效果，下面直接上代码：

实体类book:

package test.entity;
public class Book {
	private int bookId;//书的ID
	private String author;//作者
	private String name;//书名
	private int price;//书价

	public int getBookId() {
		return bookId;
	}

	public void setBookId(int bookId) {
		this.bookId = bookId;
	}

	public String getAuthor() {
		return author;
	}

	public void setAuthor(String author) {
		this.author = author;
	}

	public String getName() {
		return name;
	}

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

	public int getPrice() {
		return price;
	}

	public void setPrice(int price) {
		this.price = price;
	}

	@Override
	public String toString() {
		return "Book [bookId=" + bookId + ", author=" + author + ", name="
				+ name + ", price=" + price + "]";
	}
}

jackson以及相关jar包对java以及json数据的具体处理方法，JackSonDemo类。

package test.jackson;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import test.entity.Book;
import com.fasterxml.jackson.core.JsonEncoding;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
public class JackSonDemo {
	private JsonGenerator jsonGenerator = null;
	private ObjectMapper objectMapper = null;
	private Book book = null;

	/**
	 * Junit的方法，用于给每个单元测试添加前置条件和结束条件
	 */
	@Before
	public void init() {
		// 构建一个Book实例对象并赋值
		book = new Book();
		book.setAuthor("海明威");
		book.setBookId(123);
		book.setName("老人与海");
		book.setPrice(30);
		objectMapper = new ObjectMapper();
		try {
			jsonGenerator = objectMapper.getJsonFactory().createJsonGenerator(
					System.out, JsonEncoding.UTF8);
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	@After
	public void destory() {
		try {
			if (jsonGenerator != null) {
				jsonGenerator.flush();
			}
			if (!jsonGenerator.isClosed()) {
				jsonGenerator.close();
			}
			jsonGenerator = null;
			objectMapper = null;
			book = null;
			System.gc();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	/********************** java常见数据类型转JSON ****************************/
	/**
	 * 1.javaBean转化成json---两种方法writeObject/writeValue均可
	 * jsonGenerator依赖于ObjectMapper创建
	 */
	@Test
	public void javaBeanToJson() {

		try {
			System.out.println("jsonGenerator");
			// 方法一
			jsonGenerator.writeObject(book);
			System.out.println();

			System.out.println("ObjectMapper");
			// 方法二
			objectMapper.writeValue(System.out, book);

		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	/**
	 * List转化成JSON，三种方式
	 */
	@Test
	public void listToJson() {
		try {
			List<Book> list = new ArrayList<Book>();
			Book bookOne = new Book();
			bookOne.setAuthor("安徒生");
			bookOne.setBookId(456);
			bookOne.setName("安徒生童话");
			bookOne.setPrice(55);
			Book bookTwo = new Book();
			bookTwo.setAuthor("安徒生");
			bookTwo.setBookId(456);
			bookTwo.setName("安徒生童话");
			bookTwo.setPrice(55);
			list.add(bookOne);
			list.add(bookTwo);
			// 方式一
			System.out.println("方式一jsonGenerator");
			jsonGenerator.writeObject(list);
			System.out.println();
			System.out.println("方式二ObjectMapper");
			// 方式二
			System.out.println(objectMapper.writeValueAsString(list));
			// 方式三
			System.out.println("方式三直接通过objectMapper的writeValue方法:");
			objectMapper.writeValue(System.out, list);
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	/**
	 * map转化成JSON,两种方式
	 */
	@Test
	public void mapToJSON() {
		try {
			Map<String, Object> map = new HashMap<String, Object>();
			map.put("name", book.getName());
			map.put("book", book);
			Book newBook = new Book();
			newBook.setAuthor("安徒生");
			newBook.setBookId(456);
			newBook.setName("安徒生童话");
			newBook.setPrice(55);
			map.put("newBook", newBook);
			System.out.println("第一种方式jsonGenerator");
			jsonGenerator.writeObject(map);
			System.out.println("");
			System.out.println("第二种方式objectMapper");
			objectMapper.writeValue(System.out, map);
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	/*********************** JSON数据类型转java数据 ********************************/
	/**
	 * json'对象'数据转化成javaBean
	 */
	@Test
	public void jsonToJavaBean() {
		String json = "{\"bookId\":\"11111\",\"author\":\"鲁迅\",\"name\":\"朝花夕拾\",\"price\":\"45\"}";
		try {
			Book book = objectMapper.readValue(json, Book.class);
			System.out.println(book);
		} catch (JsonParseException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	/**
	 * json'数组'数据转化为ArrayList
	 */
	@Test
	public void jsonToArrayList() {
		String json = "[{\"bookId\":\"11111\",\"author\":\"鲁迅\",\"name\":\"朝花夕拾\",\"price\":\"45\"},"
				+ "{\"bookId\":\"11111\",\"author\":\"鲁迅\",\"name\":\"朝花夕拾\",\"price\":\"45\"}]";
		try {
			Book[] book = objectMapper.readValue(json, Book[].class);
			for (int i = 0; i < book.length; i++) {
				// 注意book[i]仅仅是数组，需要通过Arrays.asList()方法转为ArrayList
				List<Book> list = Arrays.asList(book[i]);
				System.out.println(list);

			}

		} catch (JsonParseException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	/**
	 * json转换成map
	 */
	@Test
	public void JsonToMap() {
		String json = "{\"name\":\"book\",\"number\":\"12138\",\"book1\":{\"bookId\":\"11111\",\"author\":\"鲁迅\",\"name\":\"朝花夕拾\",\"price\":\"45\"},"
				+ "\"book2\":{\"bookId\":\"22222\",\"author\":\"易中天\",\"name\":\"祖先\",\"price\":\"25\"}}";
		try {
			Map<String, Map<String, Object>> maps = objectMapper.readValue(
					json, Map.class);
			Set<String> key = maps.keySet();
			Iterator<String> iter = key.iterator();
			while (iter.hasNext()) {
				String field = iter.next();
				System.out.println(field + ":" + maps.get(field));
			}
		} catch (JsonParseException e) {
			e.printStackTrace();
		} catch (JsonMappingException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
}

最后，是我们在实际开发项目中使用的jacksonUtil类，应用起来很简单，直接jacksonUtil.bean2Json(Object object)(bean转JSON)或者jacksonUtil.json2Bean(Object object)(JSON转bean)

package test.util;
import java.io.IOException;
import java.io.StringWriter;
import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

/**
 * bean转json格式或者json转bean格式, 项目中我们通常使用这个工具类进行json---java互相转化
 */
public class JacksonUtil {
	private static ObjectMapper mapper = new ObjectMapper();

	public static String bean2Json(Object obj) throws IOException {
		StringWriter sw = new StringWriter();
		JsonGenerator gen = new JsonFactory().createJsonGenerator(sw);
		mapper.writeValue(gen, obj);
		gen.close();
		return sw.toString();
	}

	public static <T> T json2Bean(String jsonStr, Class<T> objClass)
			throws JsonParseException, JsonMappingException, IOException {
		return mapper.readValue(jsonStr, objClass);
	}
}

Jackson工具类（各种转换）

首先要在项目中引入jackson的jar包（在此不做说明）

下面直接上代码

public class JacksonUtils {
    private final static ObjectMapper objectMapper = new ObjectMapper();
    private JacksonUtils() {
    }
    public static ObjectMapper getInstance() {
        return objectMapper;
    }
    /**
     * javaBean、列表数组转换为json字符串
     */
    public static String obj2json(Object obj) throws Exception {
        return objectMapper.writeValueAsString(obj);
    }
    /**
     * javaBean、列表数组转换为json字符串,忽略空值
     */
    public static String obj2jsonIgnoreNull(Object obj) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        return mapper.writeValueAsString(obj);
    }
    /**
     * json 转JavaBean
     */
    public static <T> T json2pojo(String jsonString, Class<T> clazz) throws Exception {
        objectMapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);
        return objectMapper.readValue(jsonString, clazz);
    }
    /**
     * json字符串转换为map
     */
    public static <T> Map<String, Object> json2map(String jsonString) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
        return mapper.readValue(jsonString, Map.class);
    }
    /**
     * json字符串转换为map
     */
    public static <T> Map<String, T> json2map(String jsonString, Class<T> clazz) throws Exception {
        Map<String, Map<String, Object>> map = objectMapper.readValue(jsonString, new TypeReference<Map<String, T>>() {
        });
        Map<String, T> result = new HashMap<String, T>();
        for (Map.Entry<String, Map<String, Object>> entry : map.entrySet()) {
            result.put(entry.getKey(), map2pojo(entry.getValue(), clazz));
        }
        return result;
    }
    /**
     * 深度转换json成map
     *
     * @param json
     * @return
     */
    public static Map<String, Object> json2mapDeeply(String json) throws Exception {
        return json2MapRecursion(json, objectMapper);
    }
    /**
     * 把json解析成list，如果list内部的元素存在jsonString，继续解析
     *
     * @param json
     * @param mapper 解析工具
     * @return
     * @throws Exception
     */
    private static List<Object> json2ListRecursion(String json, ObjectMapper mapper) throws Exception {
        if (json == null) {
            return null;
        }
        List<Object> list = mapper.readValue(json, List.class);
        for (Object obj : list) {
            if (obj != null && obj instanceof String) {
                String str = (String) obj;
                if (str.startsWith("[")) {
                    obj = json2ListRecursion(str, mapper);
                } else if (obj.toString().startsWith("{")) {
                    obj = json2MapRecursion(str, mapper);
                }
            }
        }
        return list;
    }
    /**
     * 把json解析成map，如果map内部的value存在jsonString，继续解析
     *
     * @param json
     * @param mapper
     * @return
     * @throws Exception
     */
    private static Map<String, Object> json2MapRecursion(String json, ObjectMapper mapper) throws Exception {
        if (json == null) {
            return null;
        }
        Map<String, Object> map = mapper.readValue(json, Map.class);
        for (Map.Entry<String, Object> entry : map.entrySet()) {
            Object obj = entry.getValue();
            if (obj != null && obj instanceof String) {
                String str = ((String) obj);
                if (str.startsWith("[")) {
                    List<?> list = json2ListRecursion(str, mapper);
                    map.put(entry.getKey(), list);
                } else if (str.startsWith("{")) {
                    Map<String, Object> mapRecursion = json2MapRecursion(str, mapper);
                    map.put(entry.getKey(), mapRecursion);
                }
            }
        }
        return map;
    }
    /**
     * 与javaBean json数组字符串转换为列表
     */
    public static <T> List<T> json2list(String jsonArrayStr, Class<T> clazz) throws Exception {
        JavaType javaType = getCollectionType(ArrayList.class, clazz);
        List<T> lst = (List<T>) objectMapper.readValue(jsonArrayStr, javaType);
        return lst;
    }
    /**
     * 获取泛型的Collection Type
     *
     * @param collectionClass 泛型的Collection
     * @param elementClasses  元素类
     * @return JavaType Java类型
     * @since 1.0
     */
    public static JavaType getCollectionType(Class<?> collectionClass, Class<?>... elementClasses) {
        return objectMapper.getTypeFactory().constructParametricType(collectionClass, elementClasses);
    }
    /**
     * map  转JavaBean
     */
    public static <T> T map2pojo(Map map, Class<T> clazz) {
        return objectMapper.convertValue(map, clazz);
    }
    /**
     * map 转json
     *
     * @param map
     * @return
     */
    public static String mapToJson(Map map) {
        try {
            return objectMapper.writeValueAsString(map);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return "";
    }
    /**
     * map  转JavaBean
     */
    public static <T> T obj2pojo(Object obj, Class<T> clazz) {
        return objectMapper.convertValue(obj, clazz);
    }
}

导入相应的包 就可以使用，个人觉得还是挺方便的！

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。