android json 反序列化 json反序列化list

使用Jackson 如何把json字符串反序列化为List呢?
(List中是自定义对象)
先看下常规的反序列化:

@Test
    public void test_reserialize(){
        String jsonInput = "{\"addrr\":{\"country\":\"中国\",\"state\":\"湖北省\",\"street\":\"清河\"},\"age\":25,\"hobby\":\"\",\"name\":\"黄威\"}";
        ObjectMapper mapper = new ObjectMapper();
        Student student;
        try {
            student = mapper.readValue(jsonInput, Student.class);
            System.out.println(student.getAddrr().getStreet());
            System.out.println(student.getName());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

运行结果:

序列化

@Test
    public void test_004(){
        List<Teacher> list=new ArrayList<Teacher>();
        Teacher t=new Teacher();
        t.setId(2);
        t.setName("雄鹰表");
        t.setTitle("aa");
        list.add(t);

        t=new Teacher();
        t.setId(3);
        t.setName("陈定生");
        t.setTitle("bb");
        list.add(t);

        t=new Teacher();
        t.setId(4);
        t.setName("张阿勇");
        t.setTitle("cc");
        list.add(t);

        ObjectMapper mapper = new ObjectMapper();
        String content;
        try {
            content = mapper.writeValueAsString(list);
            System.out.println(content);
        } catch (JsonGenerationException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

运行结果:
[{“id”:2,”title”:”aa”,”name”:”雄鹰表”},{“id”:3,”title”:”bb”,”name”:”陈定生”},{“id”:4,”title”:”cc”,”name”:”张阿勇”}]

反序列化
把上述json字符串反序列化为List
代码如下:

@Test
    public void test_006(){
        String jsonInput="[{\"id\":2,\"title\":\"aa\",\"name\":\"雄鹰表\"},{\"id\":3,\"title\":\"bb\",\"name\":\"陈定生\"},{\"id\":4,\"title\":\"cc\",\"name\":\"张阿勇\"}]";
        ObjectMapper mapper = new ObjectMapper();
        List student;
        try {
            student = mapper.readValue(jsonInput, List.class);
            System.out.println(student.size());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

运行时

没有达到预期效果,虽然反序列化成了List,但是并不是List< Teacher>,而是List< HashMap>

如何解决这个问题呢?

解决方法:使用mapper.getTypeFactory().constructParametricType

/**   
     * 获取泛型的Collection Type  
     * @param collectionClass 泛型的Collection   
     * @param elementClasses 元素类   
     * @return JavaType Java类型   
     * @since 1.0   
     */   
 public static JavaType getCollectionType(ObjectMapper mapper,Class<?> collectionClass, Class<?>... elementClasses) {   
     return mapper.getTypeFactory().constructParametricType(collectionClass, elementClasses);   
 }
    @Test
    public void test_006(){
        String jsonInput="[{\"id\":2,\"title\":\"aa\",\"name\":\"雄鹰表\"},{\"id\":3,\"title\":\"bb\",\"name\":\"陈定生\"},{\"id\":4,\"title\":\"cc\",\"name\":\"张阿勇\"}]";
        ObjectMapper mapper = new ObjectMapper();
        List student;
        try {
            student = mapper.readValue(jsonInput, getCollectionType(mapper, List.class, Teacher.class));
            System.out.println(student.size());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }