现在很多公司的项目都基于SOA架构，系统间的调用有许多方式，其中一种常见的是用HTTP协议、以JSON格式返回结果。
这使得JSON的使用更加普遍。而市面上处理JSON的框架五花八门，常见的有JSONObject、GSON、Jackson等。
现在我们来学习Jackson，及记录常用的一些例子
<dependencies> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-core</artifactId> <version>2.1.4</version> </dependency> <dependency> <groupId>com.fasterxml.jackson.core</groupId> <artifactId>jackson-databind</artifactId> <version>2.1.4</version> </dependency> </dependencies>
将Bean对象转换为JSON，在还原回来。（为了得到指定格式的日期格式，我指定了日期格式）
package com.nicchagil.demo.No001最简单的例子; import java.io.IOException; import java.sql.Timestamp; import java.text.SimpleDateFormat; import java.util.Calendar; import org.junit.Test; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.ObjectMapper; public class Call { @Test public void writeJson() throws JsonProcessingException { ObjectMapper objectMapper = new ObjectMapper(); objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:SS")); String json = objectMapper.writeValueAsString(new User(999, "Nick Huang", new Timestamp(Calendar.getInstance().getTimeInMillis()))); System.out.println(json); } @Test public void readJson() throws IOException { String json = "{\"id\":999,\"name\":\"Nick Huang\",\"birthday\":\"2015-10-21 15:45:673\"}"; ObjectMapper objectMapper = new ObjectMapper(); objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:SS")); User user = objectMapper.readValue(json, User.class); System.out.println(user); } }
还需要一个Bean类型
package com.nicchagil.demo.No001最简单的例子; import java.sql.Timestamp; public class User { private Integer id; private String name; private Timestamp birthday; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Timestamp getBirthday() { return birthday; } public void setBirthday(Timestamp birthday) { this.birthday = birthday; } public User(Integer id, String name, Timestamp birthday) { super(); this.id = id; this.name = name; this.birthday = birthday; } public User() { super(); } @Override public String toString() { StringBuilder builder = new StringBuilder(); builder.append("User [id=").append(id).append(", name=").append(name) .append(", birthday=").append(birthday).append("]"); return builder.toString(); } }
日志如下
{"id":999,"name":"Nick Huang","birthday":"2015-10-22 17:34:318"}
User [id=999, name=Nick Huang, birthday=2015-10-21 15:45:00.673]
package com.nicchagil.demo.No002含泛型和集合; import java.io.IOException; import java.sql.Timestamp; import java.util.Calendar; import java.util.HashMap; import java.util.Map; import org.junit.Test; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.core.type.TypeReference; import com.fasterxml.jackson.databind.ObjectMapper; public class Call { @Test public void writeJson() throws JsonProcessingException { ObjectMapper objectMapper = new ObjectMapper(); Map<String, Object> map = new HashMap<String, Object>(); map.put("Nick", new User(999, "Nick Huang", new Timestamp(Calendar.getInstance().getTimeInMillis()))); map.put("Robbin", new User(998, "Robbin", new Timestamp(Calendar.getInstance().getTimeInMillis()))); String json = objectMapper.writeValueAsString(map); System.out.println(json); } @Test public void readJson() throws IOException { String json = "{\"Robbin\":{\"id\":998,\"name\":\"Robbin\",\"birthday\":1445415635096},\"Nick\":{\"id\":999,\"name\":\"Nick Huang\",\"birthday\":1445415635096}}"; ObjectMapper objectMapper = new ObjectMapper(); Map<String, User> map = objectMapper.readValue(json, new TypeReference<Map<String, User>>() {}); System.out.println(map); } }
日志如下
{"Robbin":{"id":998,"name":"Robbin","birthday":1445506610097},"Nick":{"id":999,"name":"Nick Huang","birthday":1445506610097}}
{Robbin=User [id=998, name=Robbin, birthday=2015-10-21 16:20:35.096], Nick=User [id=999, name=Nick Huang, birthday=2015-10-21 16:20:35.096]}
比如Map里面的不同key值对应的类型不同（我这个只是土方法，有好方法的童靴提示下哦）(>_<)
package com.nicchagil.demo.No003复杂结构; import java.io.IOException; import java.sql.Timestamp; import java.util.Calendar; import java.util.HashMap; import java.util.Map; import org.junit.Test; import com.fasterxml.jackson.core.JsonProcessingException; import com.fasterxml.jackson.databind.ObjectMapper; import com.nicchagil.demo.No001最简单的例子.User; public class Call { @Test public void writeJson() throws JsonProcessingException { ObjectMapper objectMapper = new ObjectMapper(); Map<String, Object> map = new HashMap<String, Object>(); map.put("code", "success"); map.put("data", new User(999, "Nick Huang", new Timestamp(Calendar.getInstance().getTimeInMillis()))); String json = objectMapper.writeValueAsString(map); System.out.println(json); } @Test public void readJson() throws IOException { String json = "{\"data\":{\"id\":999,\"name\":\"Nick Huang\",\"birthday\":1445502596155},\"code\":\"success\"}"; ObjectMapper objectMapper = new ObjectMapper(); Map<String, Object> map = objectMapper.readValue(json, Map.class); Object data = map.get("data"); User user = objectMapper.convertValue(data, User.class); map.put("data", user); System.out.println(map); /* 打印出类型 */ System.out.println("code‘s type : " + map.get("code").getClass().toString()); System.out.println("data‘s type : " + map.get("data").getClass().toString()); } }
日志如下
{"data":{"id":999,"name":"Nick Huang","birthday":1445506936594},"code":"success"}
{data=User [id=999, name=Nick Huang, birthday=2015-10-22 16:29:56.155], code=success}
code‘s type : class java.lang.String
data‘s type : class com.nicchagil.demo.No001最简单的例子.User
原文：http://www.cnblogs.com/nick-huang/p/4901738.html