Jackson中有个ObjectMapper类很是实用，用于Java对象与JSON的互换。
1、Java对象转换为JSON：
User user=new User(); //Java Object
ObjectMapper mapper = new ObjectMapper();
mapper.writeValueAsString(user); //返回字符串
//输出格式化后的字符串(有性能损耗)
mapper.defaultPrettyPrintingWriter().writeValueAsString(user);
mapper.writeValue(new File("c:\\user.json"), user); //指定文件写入
 
//设置序列化配置(全局),设置序列化时不输出空值.
sharedMapper.getSerializationConfig().setSerializationInclusion(Inclusion.NON_NULL);
 
2、JSON反序列化为Java对象：
ObjectMapper mapper = new ObjectMapper();
//解析器支持解析单引号
mapper.configure(Feature.ALLOW_SINGLE_QUOTES,true);
//解析器支持解析结束符
mapper.configure(Feature.ALLOW_UNQUOTED_CONTROL_CHARS,true);
HashMap jsonMap = mapper.readValue(json,HashMap.class); //转换为HashMap对象

private static final String TREE_MODEL_BINDING = "{\"treekey1\":\"treevalue1\",\"treekey2\":\"treevalue2\",\"children\":[{\"childkey1\":\"childkey1\"}]}";  
    public void treeModelBinding() throws Exception{  
        ObjectMapper mapper = new ObjectMapper();  
        JsonNode rootNode = mapper.readTree(TREE_MODEL_BINDING);  
        //path与get作用相同,但是当找不到该节点的时候,返回missing node而不是Null.  
        String treekey2value = http://www.mamicode.com/rootNode.path("treekey2").getTextValue();//  
        System.out.println("treekey2value:" + treekey2value);  
        JsonNode childrenNode = rootNode.path("children");  
        String childkey1Value = childrenNode.get(0).path("childkey1").getTextValue();  
        System.out.println("childkey1Value:"+childkey1Value);  
          
        //创建根节点  
        ObjectNode root = mapper.createObjectNode();  
        //创建子节点1  
        ObjectNode node1 = mapper.createObjectNode();  
        node1.put("nodekey1",1);  
        node1.put("nodekey2",2);  
        //绑定子节点1  
        root.put("child",node1);  
        //数组节点  
        ArrayNode arrayNode = mapper.createArrayNode();  
        arrayNode.add(node1);  
        arrayNode.add(1);  
        //绑定数组节点  
        root.put("arraynode", arrayNode);  
        //JSON读到树节点  
        JsonNode valueToTreeNode = mapper.valueToTree(TREE_MODEL_BINDING);  
        //绑定JSON节点  
        root.put("valuetotreenode",valueToTreeNode);  
        //JSON绑定到JSON节点对象  
        JsonNode bindJsonNode = mapper.readValue(GENERIC_BINDING, JsonNode.class);//绑定JSON到JSON节点对象.  
        //绑定JSON节点  
        root.put("bindJsonNode",bindJsonNode);  
        System.out.println(mapper.writeValueAsString(root));  
    }