一、轉換java對象為json
第一步：創建Jackson的核心對象 ObjectMapper
第二步：使用轉換方法
常用的有：
1、writeValue(參數一，參數二)；
參數一：
(1) File：將obj對象轉換為JSON字符串，並保存到指定的文件中
(2) Writer：將obj對象轉換為JSON字符串，並將json數據填充到字符輸出流中(通常可以使用respon的getWrite()方法，獲取該類)
(3) OutputStream：將obj對象轉換為JSON字符串，並將json數據填充到字節輸出流中
參數二：
要轉換為JSON的對象
2、writeValueAsString(obj)：將對象轉為json字符串
示例代碼：
1 @WebServlet("/testJsonServlet") 2 public class TestJsonServlet extends HttpServlet { 3 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 4 5 Map<String, String[]> map = request.getParameterMap(); 6 //使用BeanUtils封裝TestUser 7 TestUser testUser = new TestUser(); 8 try { 9 BeanUtils.populate(testUser, map); 10 } catch (IllegalAccessException e) { 11 e.printStackTrace(); 12 } catch (InvocationTargetException e) { 13 e.printStackTrace(); 14 } 15 System.out.println(testUser); 16 17 ObjectMapper mapper = new ObjectMapper(); 18 response.setContentType("application/json;charset=utf-8"); 19 mapper.writeValue(response.getWriter(),testUser); 20 } 21 22 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 23 this.doPost(request, response); 24 } 25 }
訪問 /testJsonServlet?name=tom&phone=123
頁面返回的內容為
說明服務器成功將參數以json的格式發送到客戶端。
二、轉換list集合為json
與將java對象轉換為json格式大同小異，這里是將obj替換為list集合對象
看一下代碼：
1 @WebServlet("/testJsonServlet") 2 public class TestJsonServlet extends HttpServlet { 3 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 4 5 /* 6 Map<String, String[]> map = request.getParameterMap(); 7 //使用BeanUtils封裝TestUser 8 TestUser testUser = new TestUser(); 9 try { 10 BeanUtils.populate(testUser, map); 11 } catch (IllegalAccessException e) { 12 e.printStackTrace(); 13 } catch (InvocationTargetException e) { 14 e.printStackTrace(); 15 } 16 System.out.println(testUser); 17 18 ObjectMapper mapper = new ObjectMapper(); 19 response.setContentType("application/json;charset=utf-8"); 20 mapper.writeValue(response.getWriter(),testUser); 21 */ 22 23 TestUser testUser1 = new TestUser(); 24 testUser1.setName("tom"); 25 testUser1.setPhone(123); 26 27 TestUser testUser2 = new TestUser(); 28 testUser2.setName("tom"); 29 testUser2.setPhone(123); 30 31 TestUser testUser3 = new TestUser(); 32 testUser3.setName("tom"); 33 testUser3.setPhone(123); 34 35 List<TestUser> list = new ArrayList<TestUser>(); 36 list.add(testUser1); 37 list.add(testUser2); 38 list.add(testUser3); 39 40 ObjectMapper mapper = new ObjectMapper(); 41 response.setContentType("application/json;charset=utf-8"); 42 String json = mapper.writeValueAsString(list); 43 response.getWriter().write(json); 44 45 } 46 47 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 48 this.doPost(request, response); 49 } 50 }
訪問 /testJsonServlet
此時返回的是一個數組，數組中為三個json對象
三、轉換Map集合為json
同樣是將對象換做map集合，
代碼如下：
1 @WebServlet("/testJsonServlet") 2 public class TestJsonServlet extends HttpServlet { 3 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 4 5 TestUser testUser1 = new TestUser(); 6 testUser1.setName("tom"); 7 testUser1.setPhone(123); 8 9 TestUser testUser2 = new TestUser(); 10 testUser2.setName("tom"); 11 testUser2.setPhone(123); 12 13 TestUser testUser3 = new TestUser(); 14 testUser3.setName("tom"); 15 testUser3.setPhone(123); 16 17 List<TestUser> list = new ArrayList<TestUser>(); 18 list.add(testUser1); 19 list.add(testUser2); 20 list.add(testUser3); 21 22 Map<Integer, TestUser> map = new HashMap<Integer, TestUser>(); 23 map.put(1,testUser1); 24 map.put(2,testUser2); 25 map.put(3,testUser3); 26 27 ObjectMapper mapper = new ObjectMapper(); 28 response.setContentType("application/json;charset=utf-8"); 29 String json = mapper.writeValueAsString(map); 30 response.getWriter().write(json); 31 } 32 33 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 34 this.doPost(request, response); 35 } 36 }
訪問 /testJsonServlet
結果如下圖
返回的內容為，json對象，其中每個鍵值對應的value值也是一個json對象
PS
response.setContentType(MIME)的作用是使客戶端瀏覽器，區分不同種類的數據，並根據不同的MIME調用瀏覽器內不同的程序嵌入模塊來處理相應的數據。
例如web瀏覽器就是通過MIME類型來判斷文件是GIF圖片。通過MIME類型來處理json字符串。