使用Jackson 如何把json字符串反序列化为List呢（转）

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:

Java代码

1. @Test
2. publicvoid test_reserialize(){
3. String jsonInput = "{\"addrr\":{\"country\":\"中国\",\"state\":\"湖北省\",\"street\":\"清河\"},\"age\":25,\"hobby\":\"\",\"name\":\"黄威\"}";
4. ObjectMapper mapper = new ObjectMapper();
5. Student student;
6. try {
7. student = mapper.readValue(jsonInput, Student.class);
8. System.out.println(student.getAddrr().getStreet());
9. System.out.println(student.getName());
10. } catch (Exception e) {
11. e.printStackTrace();
12. }
13. }

@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

Java代码

1. @Test
2. publicvoid test_004(){
3. List<Teacher> list=new ArrayList<Teacher>();
4. Teacher t=new Teacher();
5. t.setId(2);
6. t.setName("雄鹰表");
7. t.setTitle("aa");
8. list.add(t);
10. t=new Teacher();
11. t.setId(3);
12. t.setName("陈定生");
13. t.setTitle("bb");
14. list.add(t);
16. t=new Teacher();
17. t.setId(4);
18. t.setName("张阿勇");
19. t.setTitle("cc");
20. list.add(t);
22. ObjectMapper mapper = new ObjectMapper();
23. String content;
24. try {
25. content = mapper.writeValueAsString(list);
26. System.out.println(content);
27. } catch (JsonGenerationException e) {
28. e.printStackTrace();
29. } catch (JsonMappingException e) {
30. e.printStackTrace();
31. } catch (IOException e) {
32. e.printStackTrace();
33. }
34. }

@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:

Java代码

1. @Test
2. publicvoid test_006(){
3. 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\"}]";
4. ObjectMapper mapper = new ObjectMapper();
5. List student;
6. try {
7. student = mapper.readValue(jsonInput, List.class);
8. System.out.println(student.size());
9. } catch (Exception e) {
10. e.printStackTrace();
11. }
12. }

@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

Java代码

1. /**
2. * 获取泛型的Collection Type
3. * @param collectionClass 泛型的Collection
4. * @param elementClasses 元素类
5. * @return JavaType Java类型
6. * @since 1.0
7. */
8. publicstatic JavaType getCollectionType(ObjectMapper mapper,Class<?> collectionClass, Class<?>... elementClasses) {
9. return mapper.getTypeFactory().constructParametricType(collectionClass, elementClasses);
10. }
11. @Test
12. publicvoid test_006(){
13. 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\"}]";
14. ObjectMapper mapper = new ObjectMapper();
15. List student;
16. try {
17. student = mapper.readValue(jsonInput, getCollectionType(mapper, List.class, Teacher.class));
18. System.out.println(student.size());
19. } catch (Exception e) {
20. e.printStackTrace();
21. }
22. }

/**   
     * 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();
        }
    }

运行时:

参考:Jackson将json字符串转换成泛型List

http://blog.csdn.net/hw1287789687/article/details/46955179

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作者:黄威

联系方式:[email protected]

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