[英]gson.toJson(jObj) stackoverflowerror .TypeAdapters$25.write(TypeAdapters.java:704)
我正在尝试使用gson将json对象转换为String。 下面是代码
List<Student> studs = //from db
int count = studs.size();
Integer tot_pages= count/limit;
if(page>tot_pages){
page=tot_pages;
}
Integer start=limit*page-limit;
Gson gson = new Gson();
JsonObject jObj= new JsonObject();
jObj.addProperty("page", page);
jObj.addProperty("total",tot_pages);
jObj.addProperty("records",count);
JsonArray cell = new JsonArray();
JsonArray rows = new JsonArray();
JsonObject row= new JsonObject();
for(Student stud: studs){
row= new JsonObject();
row.addProperty("id", stud.getId());
cell=new JsonArray();
JsonPrimitive name = new JsonPrimitive(stud.getName());
JsonPrimitive rollno = new JsonPrimitive(stud.getRollno());
JsonPrimitive yr = new JsonPrimitive(stud.getYr());
cell.add(name);
cell.add(rollno);
cell.add(yr);
row.add("cell", row);
rows.add(row);
System.out.println(stud.getId());
}
System.out.println("done");
jObj.add("rows", rows);
System.out.println("done1");
return gson.toJson(jObj);
并得到下面的错误
造成原因:java.lang.StringBuffer.append(StringBuffer.java:237)的java.lang.AbstractStringBuilder.append(AbstractStringBuilder.java:416)的java.io.StringWriter.write(StringWriter.java的java.lang.StackOverflowError :101),位于com.google.gson.stream.JsonWriter.string(JsonWriter.java:534),位于com.google.gson.stream.JsonWriter.writeDeferredName(JsonWriter.java:402),位于com.google.gson.stream。 com.google.gson.internal.bind.TypeAdapters $ 25.write(TypeAdapters.java:686)的com.google.gson.internal.bind.TypeAdapters $ 25.write(TypeAdapters)的JsonWriter.value(JsonWriter.java:495) com.google.gson.internal.bind.TypeAdapters $ 25.write(TypeAdapters.java:704)上com.google.gson.internal.bind.TypeAdapters $ 25.write(TypeAdapters.java:704)上的java:704)在com.google.gson.internal.bind.TypeAdapters $ 25.write(TypeAdapters.java:704)在com.google.gson.internal的.google.gson.internal.bind.TypeAdapters $ 25.write(TypeAdapters.java:704) .bind.TypeAdapters $ 25.write(TypeAdapters.java:704)<-----此行重复 d很多次。
请有人帮我。
更改:
row.add("cell", row);
至:
row.add("cell", cell);
Gson
一句, Gson
对象非常强大,应该能够序列化学生列表,而无需使用您现在正在使用的所有手动代码。 最糟糕的是,您应该考虑为您的学生班级创建TypeAdapter
,向Gson注册它,并序列化为列表:
假设学生班:
public class Student implements Serializable {
private static final long serialVersionUID = 1L;
private String ssn;
private String schoolId;
private String firstName;
private String middleName;
private String lastName;
private Calendar enrollDate;
// Constructors, getters/setters
@Override
public String toString() {
return String.format("Student[%s,%s (%s)]", getLastName(),
getFirstName(), getSchoolId());
}
}
对应的适配器:
public class StudentAdapter extends TypeAdapter<Student> {
public StudentAdapter() {
super();
}
@Override
public Student read(final JsonReader reader) throws IOException {
if (reader.peek() == JsonToken.NULL) {
reader.nextNull();
return null;
}
final Student student = new Student();
reader.beginObject();
while (reader.hasNext()) {
final String name = reader.nextName();
if ("firstName".equals(name)) {
student.setFirstName(reader.nextString());
} else if ("lastName".equals(name)) {
student.setLastName(reader.nextString());
} else if ("schoolId".equals(name)) {
student.setSchoolId(reader.nextString());
}
}
reader.endObject();
return student;
}
@Override
public void write(final JsonWriter writer, final Student student)
throws IOException {
if (student == null) {
writer.nullValue();
return;
}
writer.beginObject();
writer.name("firstName");
writer.value(student.getFirstName());
writer.name("lastName");
writer.value(student.getLastName());
writer.name("schoolId");
writer.value(student.getSchoolId());
writer.endObject();
}
}
测试代码:
final List<Student> origStudentList = Arrays.asList(new Student(
"B12J9", "Samantha", "Cole"), new Student("A09K2", "Adebisi",
"Onihan"), new Student(null, "Miguel", "Rodriguez"));
final Gson gson = new GsonBuilder().registerTypeAdapter(Student.class,
new StudentAdapter()).create();
final String json = gson.toJson(origStudentList);
System.out.println(json);
final List<Student> unmarshalledStudentList = gson.fromJson(json,
new TypeToken<List<Student>>() {
}.getType());
System.out.println(unmarshalledStudentList);
在上面的示例中,我说明了如何创建一个适配器,该适配器选择性地schoolId
假设的Student
对象的schoolId
, firstName
和lastName
属性进行序列化。 您可以以此为起点,并且在我链接的Javadoc中还有其他类型适配器的示例。
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