Jackson常用方法以及jacksonUtil工具类

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);}}