Jacksonfasterxml和codehaus的区别：
他们是Jackson的两大分支、也是两个版本的不同包名。Jackson从2.0开始改用新的包名fasterxml；1.x版本的包名是codehaus。除了包名不同，他们的Maven artifact id也不同。1.x版本现在只提供bug-fix，而2.x版本还在不断开发和发布中。如果是新项目，建议直接用2x，即fasterxml jackson。
Jackson可以轻松的将Java对象转换成json对象和xml文档，同样也可以将json、xml转换成Java对象。
三个主要的模块：
jackson-core：核心包
jackson-annotations：注解包
jackson-databind：数据绑定包
jackson-databind需要引用另外两个包，所以如果项目中需要jackson-databind，则只需要加入它的dependency就行了，其他两个会自动引入：
<dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.5.3</version> </dependency>Examples:
//Map转化为json Map<String, String> hashMap = new HashMap<String, String>(); hashMap.put("name", "zhang"); hashMap.put("sex", "1"); hashMap.put("login", "Jack"); hashMap.put("password", "123abc"); try { ObjectMapper objectMapper = new ObjectMapper(); String userMapJson = objectMapper.writeValueAsString(hashMap); JsonNode node = objectMapper.readTree(userMapJson); // 输出结果转意，输出正确的信息 System.out.println(node.get("password").asText());//123abc // 输出不转意,输出结果会包含""，这是不正确的，除非作为json传递，如果是输出结果值，必须如上一行的操作 System.out.println(node.get("password"));//"123abc" } catch (IOException e) { } // 解析 json 格式字符串 String str = "{\"data\":{\"birth_day\":7,\"birth_month\":6},\"errcode\":0,\"msg\":\"ok\",\"ret\":0}"; ObjectMapper mapper = new ObjectMapper(); JsonNode root = mapper.readTree(str);//{"data":{"birth_day":7,"birth_month":6},"errcode":0,"msg":"ok","ret":0} JsonNode data = root.path("data");//{"birth_day":7,"birth_month":6} JsonNode birth_day = data.path("birth_day");//7 System.out.println(birth_day.asInt());// JsonNode birth_month = data.path("birth_month");//6 System.out.println(birth_month.asInt()); JsonNode msg = root.path("msg"); System.out.println(msg.textValue());//"ok" //json 直接提取值 try { // 演示字符串 /** * { "data": { "hasnext": 0, "info": [ { "id": "288206077664983", "timestamp": 1371052476 }, { "id": "186983078111768", "timestamp": 1370944068 }, { "id": "297031120529307", "timestamp": 1370751789 }, { "id": "273831022294863", "timestamp": 1369994812 } ], "timestamp": 1374562897, "totalnum": 422 }, "errcode": 0, "msg": "ok", "ret": 0, "seqid": 5903702688915195000 } */ String str = "{\"data\":{\"hasnext\":0,\"info\":[{\"id\":\"288206077664983\",\"timestamp\":1371052476},{\"id\":\"186983078111768\",\"timestamp\":1370944068},{\"id\":\"297031120529307\",\"timestamp\":1370751789},{\"id\":\"273831022294863\",\"timestamp\":1369994812}],\"timestamp\":1374562897,\"totalnum\":422},\"errcode\":0,\"msg\":\"ok\",\"ret\":0,\"seqid\":5903702688915195270}"; ObjectMapper mapper = new ObjectMapper(); JsonNode root = mapper.readTree(str); // 提取 data JsonNode data = root.path("data"); // 提取 info JsonNode info = data.path("info"); System.out.println(info.size()); // 得到 info 的第 0 个 JsonNode item = info.get(0); System.out.println(item.get("id")); System.out.println(item.get("timestamp")); // 得到 info 的第 2 个 item = info.get(2); System.out.println(item.get("id")); System.out.println(item.get("timestamp")); // 遍历 info 内的 array if (info.isArray()) { for (JsonNode objNode : info) { System.out.println(objNode); } } } catch (Exception e) { } //创建一个 json，并向该 json 添加内容 try { ObjectMapper mapper = new ObjectMapper(); ObjectNode root1 = mapper.createObjectNode(); root1.put("nodekey1", 1); root1.put("nodekey2", 2); System.out.println(root1.toString());//{"nodekey1":1,"nodekey2":2} //Create the root node ObjectNode root = mapper.createObjectNode(); //Create a child node ObjectNode node1 = mapper.createObjectNode(); node1.put("nodekey1", 1); node1.put("nodekey2", 2); //Bind the child nodes root.put("child", node1);//{"child":{"nodekey1":1,"nodekey2":2}} //Array of nodes ArrayNode arrayNode = mapper.createArrayNode();//[] arrayNode.add(node1); arrayNode.add(1);//[{"nodekey1":1,"nodekey2":2},1] //Bind array node root.put("arraynode", arrayNode);//{"child":{"nodekey1":1,"nodekey2":2},"arraynode":[{"nodekey1":1,"nodekey2":2},1]} System.out.println(mapper.writeValueAsString(root));//{"child":{"nodekey1":1,"nodekey2":2},"arraynode":[{"nodekey1":1,"nodekey2":2},1]} } catch (Exception e) { } //创建一个 array node try { ObjectMapper mapper = new ObjectMapper(); ArrayNode arrayNode = mapper.createArrayNode();//[] int i = 0; // 在 array 内创建 3 组 node 存入 array for (i = 0; i < 3; i++) { // 创建一个 node ObjectNode node = mapper.createObjectNode(); node.put("nodeA", i); node.put("nodeB", i); node.put("nodeC", i); // 向 array 内添 node arrayNode.add(node); } ObjectNode root = mapper.createObjectNode(); root.put("total", i); //或 root.set ("rows", arrayNode); root.put("rows", arrayNode);// {"total":3,"rows":[{"nodeA":0,"nodeB":0,"nodeC":0},{"nodeA":1,"nodeB":1,"nodeC":1},{"nodeA":2,"nodeB":2,"nodeC":2}]} System.out.println(mapper.writeValueAsString(root)); } catch (Exception e) { } // 将 java对象转换为 json string ObjectWriter objectWriter = new ObjectMapper().writer().withDefaultPrettyPrinter(); String json = null; try { json = objectWriter.writeValueAsString(new Student("lihongbing","1")); System.out.println(json);//{"name" : "lihongbing","grade" : "1"} } catch (JsonProcessingException e) { e.printStackTrace(); }
