Entity中Lazy Load的属性序列化JSON时报错
The server encountered an internal error that prevented it from fulfilling
this request.org.springframework.http.converter.HttpMessageNotWritableException:
Could not write JSON: failed to lazily initialize a collection of role:
com.party.dinner.entity.User.friends, could not initialize proxy - no Session
(through reference chain:
com.party.dinner.entity.User["friends"]); nested exception is
org.codehaus.jackson.map.JsonMappingException: failed to lazily initialize a
collection of role: com.party.dinner.entity.User.friends, could not initialize
proxy - no Session (through reference chain:
com.party.dinner.entity.User["friends"])
org.springframework.http.converter.json.MappingJacksonHttpMessageConverter.writeInternal(MappingJacksonHttpMessageConverter.java:204)
org.springframework.http.converter.AbstractHttpMessageConverter.write(AbstractHttpMessageConverter.java:179)
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter$ServletHandlerMethodInvoker.writeWithMessageConverters(AnnotationMethodHandlerAdapter.java:1037)
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter$ServletHandlerMethodInvoker.handleResponseBody(AnnotationMethodHandlerAdapter.java:995)
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter$ServletHandlerMethodInvoker.getModelAndView(AnnotationMethodHandlerAdapter.java:944)
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:441)
org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:428)
org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:925)
org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)
org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)
javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)
javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
root cause
org.codehaus.jackson.map.JsonMappingException: failed
to lazily initialize a collection of role: com.party.dinner.entity.User.friends,
could not initialize proxy - no Session (through reference chain:
com.party.dinner.entity.User["friends"])
org.codehaus.jackson.map.JsonMappingException.wrapWithPath(JsonMappingException.java:218)
org.codehaus.jackson.map.JsonMappingException.wrapWithPath(JsonMappingException.java:183)
org.codehaus.jackson.map.ser.std.SerializerBase.wrapAndThrow(SerializerBase.java:140)
org.codehaus.jackson.map.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:158)
org.codehaus.jackson.map.ser.BeanSerializer.serialize(BeanSerializer.java:112)
org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:610)
org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:256)
org.codehaus.jackson.map.ObjectMapper.writeValue(ObjectMapper.java:1613)
转载:http://blog.csdn.net/nomousewch/article/details/8955796
jackson在实际应用中给我们提供了一系列注解,提高了开发的灵活性,下面介绍一下最常用的一些注解
- @JsonIgnoreProperties
此注解是类注解,作用是json序列化时将java bean中的一些属性忽略掉,序列化和反序列化都受影响。
- @JsonIgnore
此注解用于属性或者方法上(最好是属性上),作用和上面的@JsonIgnoreProperties一样。
- @JsonFormat
此注解用于属性或者方法上(最好是属性上),可以方便的把Date类型直接转化为我们想要的模式,比如@JsonFormat(pattern = "yyyy-MM-dd HH-mm-ss")
- @JsonSerialize
此注解用于属性或者getter方法上,用于在序列化时嵌入我们自定义的代码,比如序列化一个double时在其后面限制两位小数点。
- public class CustomDoubleSerialize extends JsonSerializer<Double> {
- private DecimalFormat df = new DecimalFormat("##.00");
- @Override
- public void serialize(Double value, JsonGenerator jgen,
- SerializerProvider provider) throws IOException,
- JsonProcessingException {
- jgen.writeString(df.format(value));
- }
- }
- @JsonDeserialize
此注解用于属性或者setter方法上,用于在反序列化时可以嵌入我们自定义的代码,类似于上面的@JsonSerialize
- public class CustomDateDeserialize extends JsonDeserializer<Date> {
- private SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
- @Override
- public Date deserialize(JsonParser jp, DeserializationContext ctxt)
- throws IOException, JsonProcessingException {
- Date date = null;
- try {
- date = sdf.parse(jp.getText());
- } catch (ParseException e) {
- e.printStackTrace();
- }
- return date;
- }
- }
- 完整例子
- //表示序列化时忽略的属性
- @JsonIgnoreProperties(value = { "word" })
- public class Person {
- private String name;
- private int age;
- private boolean sex;
- private Date birthday;
- private String word;
- private double salary;
- public String getName() {
- return name;
- }
- public void setName(String name) {
- this.name = name;
- }
- public int getAge() {
- return age;
- }
- public void setAge(int age) {
- this.age = age;
- }
- public boolean isSex() {
- return sex;
- }
- public void setSex(boolean sex) {
- this.sex = sex;
- }
- public Date getBirthday() {
- return birthday;
- }
- // 反序列化一个固定格式的Date
- @JsonDeserialize(using = CustomDateDeserialize.class)
- public void setBirthday(Date birthday) {
- this.birthday = birthday;
- }
- public String getWord() {
- return word;
- }
- public void setWord(String word) {
- this.word = word;
- }
- // 序列化指定格式的double格式
- @JsonSerialize(using = CustomDoubleSerialize.class)
- public double getSalary() {
- return salary;
- }
- public void setSalary(double salary) {
- this.salary = salary;
- }
- public Person(String name, int age) {
- this.name = name;
- this.age = age;
- }
- public Person(String name, int age, boolean sex, Date birthday,
- String word, double salary) {
- super();
- this.name = name;
- this.age = age;
- this.sex = sex;
- this.birthday = birthday;
- this.word = word;
- this.salary = salary;
- }
- public Person() {
- }
- @Override
- public String toString() {
- return "Person [name=" + name + ", age=" + age + ", sex=" + sex
- + ", birthday=" + birthday + ", word=" + word + ", salary="
- + salary + "]";
- }
- }
- public class Demo {
- public static void main(String[] args) {
- writeJsonObject();
- // readJsonObject();
- }
- // 直接写入一个对象(所谓序列化)
- public static void writeJsonObject() {
- ObjectMapper mapper = new ObjectMapper();
- Person person = new Person("nomouse", 25, true, new Date(), "程序员",
- 2500.0);
- try {
- mapper.writeValue(new File("c:/person.json"), person);
- } catch (JsonGenerationException e) {
- e.printStackTrace();
- } catch (JsonMappingException e) {
- e.printStackTrace();
- } catch (IOException e) {
- e.printStackTrace();
- }
- }
- // 直接将一个json转化为对象(所谓反序列化)
- public static void readJsonObject() {
- ObjectMapper mapper = new ObjectMapper();
- try {
- Person person = mapper.readValue(new File("c:/person.json"),
- Person.class);
- System.out.println(person.toString());
- } catch (JsonParseException e) {
- e.printStackTrace();
- } catch (JsonMappingException e) {
- e.printStackTrace();
- } catch (IOException e) {
- e.printStackTrace();
- }
- }
- }
- 如果Entity中的延迟加载对象必须有值,可以用Hibernate.initialize把延迟加载的对象提前获取
- Hibernate.initialize( Entity.getXX() );
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