FastJson 之 JSONPath的使用

叙述

jsonpath，类似于xpath。都是通过一种字符串表达式，来快捷检索json里面的数据。在非常复杂的json结构中，对于一些获取和判断操作，不需要层层的去get。可以通过简洁的JsonPath表达式获取到结果。

解析

JSONPath

构造方法

public JSONPath(String path)
public JSONPath(String path, SerializeConfig serializeConfig, ParserConfig parserConfig)

静态属性/方法

public static Object eval(Object rootObject, String path)
public static Object extract(String json, String path, ParserConfig config, int features, Feature... optionFeatures)
public static Object extract(String json, String path) 
	* 根据path检索值
	* extract,按需计算, 性能会更好

public static int size(Object rootObject, String path) 
	* 计算Size
	* Map非空元素个数, 对象非空元素个数, Collection的Size, 数组的长度
	* 其他无法求值返回-1

public static Set<?> keySet(Object rootObject, String path)	
	* 获取, Map的KeySet, 对象非空属性的名称
	* 数组, Collection等不支持类型返回null

public static boolean contains(Object rootObject, String path)
	* 是否包含, path中是否存在对象
	
public static boolean containsValue(Object rootObject, String path, Object value)
	* 是否包含, path中是否存在指定值
	* 如果是集合或者数组, 在集合中查找value是否存在

public static void arrayAdd(Object rootObject, String path, Object... values)
	 * 在数组或者集合中添加元素, 添加成功返回 true,失败返回 false

public static boolean set(Object rootObject, String path, Object value)
	* 修改制定路径的值, 如果修改成功, 返回true, 否则返回false

public static boolean remove(Object root, String path)
	* 删除指定path的元素, 删除成功返回 true,失败返回 false

public static JSONPath compile(String path)
	* 编译一个jsonpath为对象

public static Object read(String json, String path)
	* 从一个json字符串中, 根据指定的path读取为Json对象

public static Map<String, Object> paths(Object javaObject)
public static Map<String, Object> paths(Object javaObject, SerializeConfig config)
	* 返回指定Java对象的属性的所有json访问path

看到这里也能明白，如果一个JsonPath需要多次重复使用的话，建议创建维护一个对象。而不是使用静态方法。

JsonPath支持的语法

Demo

public void test_entity() throws Exception {
   Entity entity = new Entity(123, new Object());
   
  Assert.assertSame(entity.getValue(), JSONPath.eval(entity, "$.value")); 
  Assert.assertTrue(JSONPath.contains(entity, "$.value"));
  Assert.assertTrue(JSONPath.containsValue(entity, "$.id", 123));
  Assert.assertTrue(JSONPath.containsValue(entity, "$.value", entity.getValue())); 
  Assert.assertEquals(2, JSONPath.size(entity, "$"));
  Assert.assertEquals(0, JSONPath.size(new Object[], "$")); 
}

public static class Entity {
   private Integer id;
   private String name;
   private Object value;

   public Entity() {}
   public Entity(Integer id, Object value) { this.id = id; this.value = value; }
   public Entity(Integer id, String name) { this.id = id; this.name = name; }
   public Entity(String name) { this.name = name; }

   public Integer getId() { return id; }
   public Object getValue() { return value; }        
   public String getName() { return name; }
   
   public void setId(Integer id) { this.id = id; }
   public void setName(String name) { this.name = name; }
   public void setValue(Object value) { this.value = value; }
}

Demo - 读取数据

List<Entity> entities = new ArrayList<Entity>();
entities.add(new Entity("wenshao"));
entities.add(new Entity("ljw2083"));

List<String> names = (List<String>)JSONPath.eval(entities, "$.name"); // 返回enties的所有名称
Assert.assertSame(entities.get(0).getName(), names.get(0));
Assert.assertSame(entities.get(1).getName(), names.get(1));

Demo2 - 返回集合中多个元素

List<Entity> entities = new ArrayList<Entity>();
entities.add(new Entity("wenshao"));
entities.add(new Entity("ljw2083"));

List<String> names = (List<String>)JSONPath.eval(entities, "$.name"); // 返回enties的所有名称
Assert.assertSame(entities.get(0).getName(), names.get(0));
Assert.assertSame(entities.get(1).getName(), names.get(1));

Demo3 - 按范围返回集合的子集

List<Entity> entities = new ArrayList<Entity>();
entities.add(new Entity("wenshao"));
entities.add(new Entity("ljw2083"));
entities.add(new Entity("Yako"));

List<Entity> result = (List<Entity>)JSONPath.eval(entities, "[0:2]"); // 返回下标从0到2的元素
Assert.assertEquals(3, result.size());
Assert.assertSame(entities.get(0), result.get(0));
Assert.assertSame(entities.get(1), result.get(1));
Assert.assertSame(entities.get(2), result.get(1));

Demo4 - 通过条件过滤，返回集合的子集

List<Entity> entities = new ArrayList<Entity>();
entities.add(new Entity(1001, "ljw2083"));
entities.add(new Entity(1002, "wenshao"));
entities.add(new Entity(1003, "yakolee"));
entities.add(new Entity(1004, null));

List<Object> result = (List<Object>) JSONPath.eval(entities, "[id in (1001)]");
Assert.assertEquals(1, result.size());
Assert.assertSame(entities.get(0), result.get(0));

Demo5 - 根据属性值过滤条件判断是否返回对象，修改对象，数组属性添加元素

Entity entity = new Entity(1001, "ljw2083");
Assert.assertSame(entity , JSONPath.eval(entity, "[id = 1001]"));
Assert.assertNull(JSONPath.eval(entity, "[id = 1002]"));

JSONPath.set(entity, "id", 123456); //将id字段修改为123456
Assert.assertEquals(123456, entity.getId().intValue());

JSONPath.set(entity, "value", new int[0]); //将value字段赋值为长度为0的数组
JSONPath.arrayAdd(entity, "value", 1, 2, 3); //将value字段的数组添加元素1,2,3

Demo6

Map root = Collections.singletonMap("company", //
                                    Collections.singletonMap("departs", //
                                                             Arrays.asList( //
                                                                            Collections.singletonMap("id",
                                                                                                     1001), //
                                                                            Collections.singletonMap("id",
                                                                                                     1002), //
                                                                            Collections.singletonMap("id", 1003) //
                                                             ) //
                                    ));

List<Object> ids = (List<Object>) JSONPath.eval(root, "$..id");
assertEquals(3, ids.size());
assertEquals(1001, ids.get(0));
assertEquals(1002, ids.get(1));
assertEquals(1003, ids.get(2));

Demo - 7 KeySet

使用keySet抽取对象的属性名，null值属性的名字并不包含在keySet结果中，使用时需要注意

Entity e = new Entity();
e.setId(null);
e.setName("hello");
Map<String, Entity> map = Collections.singletonMap("e", e);
Collection<String> result;

// id is null, excluded by keySet
result = (Collection<String>)JSONPath.eval(map, "$.e.keySet()");
assertEquals(1, result.size());
Assert.assertTrue(result.contains("name"));

e.setId(1L);
result = (Collection<String>)JSONPath.eval(map, "$.e.keySet()");
Assert.assertEquals(2, result.size());
Assert.assertTrue(result.contains("id")); // included
Assert.assertTrue(result.contains("name"));

// Same result
Assert.assertEquals(result, JSONPath.keySet(map, "$.e"));
Assert.assertEquals(result, new JSONPath("$.e").keySet(map));

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FastJson 之 JSONPath的使用

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