jackson 的使用示例
寫在前面
關於 java 對象的序列化與反序列化的問題，最近 阿里的fastJson在網上噓聲一片，很多遺留的Bug、issue都未解決等等…
其實也不要太警惕，java 的基本開發中，web開發、大數據開發，我目前接觸、瞭解的也就這兩個主流開發方向，關於對象的構造不是很複雜的話，阿里的FastJson就可以很方便的準確序列化，但是，目前中國，也存在一些真正的大牛、團隊（類似阿里。騰訊，網易、百度等等大廠）在高級的框架設計中，會有頻繁的序列化與反序列化的對象操作，這樣可能對序列化要有更加準確的解析，類似 Spring ，Mybatis,apache 等等，他們都是基於 Jackson（fasterxml ）封裝的對象序列化實現方案…
一、簡單比較
這裏比較下，FastJson、Gson、fasterxml jackson的相關基礎
-
FastJson
![在這裏插入圖片描述]()
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Gson
![在這裏插入圖片描述]()
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jackson
基本性能測試、有興趣的可以去自己測試，序列化/反序列化最重要的準確解析數據。速度不是最重要的
二 、fastJson
2.1、示例一
/**
* {"id":123,"name":"一級部門"}
* @throws Exception
*/
public void test_0() throws Exception {
Department dep = new Department();
dep.setId(123);
dep.setName("一級部門");
dep.setParent(dep);
String text = JSON.toJSONString(dep);
System.out.println(text);
JSON.parseObject(text, Department.class);
}
public static class Department {
private int id;
private String name;
private Department parent;
private transient List<Department> children = new ArrayList<Department>();
public int getId() { return id; }
public void setId(int id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
@JSONField(serialize=false)
public Department getParent() { return parent; }
public void setParent(Department parent) { this.parent = parent; }
public List<Department> getChildren() { return children; }
public void setChildren(List<Department> children) { this.children = children; }
}
2.2、示例二
/**
* {"name":"Jobs","salary":8000,"age":50}
* @throws Exception
*/
public void test_0() throws Exception {
JSONObject jsonObject = new JSONObject();
jsonObject.put("name", "Jobs");
jsonObject.put("age", 50);
jsonObject.put("salary", new BigDecimal(8000));
String text = jsonObject.toJSONString();
System.out.println(text);
}
2.3、示例三
/**
* {"id":0,"name":"admin","users":[{"id":2,"name":"guest"},{"id":3,"name":"root"}]}
* @throws Exception
*/
public void test_encode() throws Exception {
Group group = new Group();
group.setId(0L);
group.setName("admin");
User guestUser = new User();
guestUser.setId(2L);
guestUser.setName("guest");
User rootUser = new User();
rootUser.setId(3L);
rootUser.setName("root");
group.getUsers().add(guestUser);
group.getUsers().add(rootUser);
String jsonString = JSON.toJSONString(group);
System.out.println(jsonString);
JSON.parseObject(jsonString, Group.class);
}
2.4、示例四,name ,value 過濾
public void test_secure() throws Exception {
ValueFilter filter = new ValueFilter() {
public Object process(Object source, String name, Object value) {
if (name.equals("name")) {
return "WSJ";
}
return value;
}
};
NameFilter nameFilter = new NameFilter() {
public String process(Object source, String name, Object value) {
if (name.equals("id")) {
return "ID";
}
return name;
}
};
String text = "{\"id\":123,\"name\":\"WJH\"}";
Object object = JSON.parse(text);
SerializeWriter out = new SerializeWriter();
JSONSerializer serializer = new JSONSerializer(out);
serializer.getValueFilters().add(filter);
serializer.getNameFilters().add(nameFilter);
serializer.write(object);
String outText = out.toString();
System.out.println(outText);
}
2.5、demo5, @JSONField 使用
public static class User {
private int id;
private String name;
@JSONField(name = "uid")
public int getId() { return id; }
@JSONField(name = "uid")
public void setId(int id) { this.id = id; }
public String getName() { return name; }
public void setName(String name) { this.name = name; }
}
/**
* {"name":"毛頭","uid":123}
* @throws Exception
*/
public void test_0() throws Exception {
User user = new User();
user.setId(123);
user.setName("毛頭");
String text = JSON.toJSONString(user);
Assert.assertEquals("{\"name\":\"毛頭\",\"uid\":123}", text);
System.out.println(text);
}
2.6、demo 6
/**
* {"name":"張三","id":123}
* {name=張三, id=123}
*/
public class MapDemo extends TestCase {
public void test_0 () throws Exception {
Map<String, Object> map = new HashMap<String, Object>();
map.put("id", 123);
map.put("name", "張三");
String text = JSON.toJSONString(map);
System.out.println(text);
System.out.println(map.toString());
}
}
2.7、DefaultJSONParser
public void test_reuse() throws Exception {
Model model = new Model();
{
DefaultJSONParser parser = new DefaultJSONParser("{\"id\":123,\"name\":\"wangsai-silence\"}");
parser.parseObject(model);
parser.close(); // 調用close能重用buf，提升性能
assertEquals(123, model.id);
assertEquals("wangsai-silence", model.name);
}
{
DefaultJSONParser parser = new DefaultJSONParser("{\"id\":234,\"name\":\"wenshao\"}");
parser.parseObject(model);
parser.close(); // 調用close能重用buf，提升性能
assertEquals(234, model.id);
assertEquals("wenshao", model.name);
}
}
public static class Model {
public int id;
public String name;
}
2.8、從文件中解析
public void test_for_maiksagill() throws Exception {
String resource = "json/maiksagill.json";
InputStream is = Thread.currentThread().getContextClassLoader().getResourceAsStream(resource);
String text = IOUtils.toString(is);
System.out.println(text);
JSON.parseObject(text, WareHouseInfo[].class);
}
2.9、Null 處理
public void test_boolean() throws Exception {
Model model = new Model();
// String json = JSON.toJSONString(model, SerializerFeature.IgnoreNonFieldGetter); //{}
String json = JSON.toJSONString(model,SerializerFeature.WriteNullStringAsEmpty); // {"available":true,"name":""}
// String json = JSON.toJSONString(model,SerializerFeature.WriteMapNullValue); // {"age":null,"available":true,"name":null}
System.out.println(json);
}
public static class Model {
private String name;
private Long age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Long getAge() {
return age;
}
public void setAge(Long age) {
this.age = age;
}
public boolean isAvailable() {
return true;
}
}
簡單列出這麼多，其實 FastJson還是很強大的，比Gson ,Jackson 豐富很多序列化的實現
三、Gson
這裏可參考這裏，鏈接
四、Jackson
Jackson是框架設計中首選的，是可以肯定的