jackson常用方法详解

最近一老使用Jackson来进行转换json类型数据，现将其常用的方法记录下来，以备查阅。

 private JsonGenerator jsonGenerator = null;  
 private ObjectMapper objectMapper = null;  
 
 private Book book = null;  
/********************** 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);  
    }  
}