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IDprivate 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;} @Overridepublic 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 */@Beforepublic 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();}} @Afterpublic 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 */@Testpublic 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 */@Testpublic 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 */@Testpublic 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 */@Testpublic 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 */@Testpublic 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ArrayListList<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 */@Testpublic 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。
山不厌高，水不厌深。
