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","price":"45"},"
+ "{"bookId":"11111","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","
+ ""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);
}
}
