Gson full resolution (middle) - the use of TypeAdapter

To complete the traversal of each JsonElement, and obtain the key value pairs in the Json object through the method of switch...case. And set it through the Setter method of our Book entity class.

while (in.hasNext()) { switch (in.nextName()) { case "isbn": book.setIsbn(in.nextString()); break; case "title": book.setTitle(in.nextString()); break; case "authors": book.setAuthors(in.nextString().split(";")); break; } }

• It should also be noted that if in.endObject() is not executed, there will be an error of JsonIOException:

Exception in thread "main" com.google.gson.JsonIOException: JSON document was not fully consumed. at com.google.gson.Gson.assertFullConsumption(Gson.java:776) at com.google.gson.Gson.fromJson(Gson.java:769) at com.google.gson.Gson.fromJson(Gson.java:717) at com.google.gson.Gson.fromJson(Gson.java:689) at com.javacreed.examples.gson.part1.Main.main(Main.java:41)

The complete code to use the TypeAdapter is as follows:

package com.javacreed.examples.gson.part1; import java.io.IOException; import com.google.gson.Gson; import com.google.gson.GsonBuilder; public class Main { public static void main(final String[] args) throws IOException { final GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.registerTypeAdapter(Book.class, new BookTypeAdapter()); gsonBuilder.setPrettyPrinting(); final Gson gson = gsonBuilder.create(); final Book book = new Book(); book.setAuthors(new String[] { "Joshua Bloch", "Neal Gafter" }); book.setTitle("Java Puzzlers: Traps, Pitfalls, and Corner Cases"); book.setIsbn("978-0321336781"); final String json = gson.toJson(book); System.out.println("Serialised"); System.out.println(json); final Book parsedBook = gson.fromJson(json, Book.class); System.out.println("\nDeserialised"); System.out.println(parsedBook); } }

The corresponding compilation results are:

Serialised { "isbn": "978-0321336781", "title": "Java Puzzlers: Traps, Pitfalls, and Corner Cases", "authors": "Joshua Bloch;Neal Gafter" } Deserialised Java Puzzlers: Traps, Pitfalls, and Corner Cases [978-0321336781] Written by: >> Joshua Bloch >> Neal Gafter

TypeAdapter handles simple JSON data

In order to simplify JSON data, in fact, the above JSON data can be written as follows:

["978-0321336781","Java Puzzlers: Traps, Pitfalls, and Corner Cases","Joshua Bloch","Neal Gafter"]

As you can see, this is in the form of values. Of course, this operation simplifies JSON data, but may reduce the stability of the whole data. You need to parse the data in a certain order.
The corresponding write and read methods are as follows:

@Override public void write(final JsonWriter out, final Book book) throws IOException { out.beginArray(); out.value(book.getIsbn()); out.value(book.getTitle()); for (final String author : book.getAuthors()) { out.value(author); } out.endArray(); }

@Override public Book read(final JsonReader in) throws IOException { final Book book = new Book(); in.beginArray(); book.setIsbn(in.nextString()); book.setTitle(in.nextString()); final List authors = new ArrayList<>(); while (in.hasNext()) { authors.add(in.nextString()); } book.setAuthors(authors.toArray(new String[authors.size()])); in.endArray(); return book; }

The analytical principle here is consistent with the above, and will not be repeated.

TypeAdapter resolving built-in objects

(here, the nested objects are translated into built-in objects, which are actually in the Book class.)

Here, the above Book entity class is modified as follows. Add the Author class. Each Book can have multiple authors.

package com.javacreed.examples.gson.part3; public class Book { private Author[] authors; private String isbn; private String title; class Author { private int id; private String name; //For code simplicity, remove getter and setter methods, etc } //For code simplicity, remove getter and setter methods, etc }

JSON objects are provided here,

{ "isbn": "978-0321336781", "title": "Java Puzzlers: Traps, Pitfalls, and Corner Cases", "authors": [ { "id": 1, "name": "Joshua Bloch" }, { "id": 2, "name": "Neal Gafter" } ] }

Here are the write and read methods:

@Override public void write(final JsonWriter out, final Book book) throws IOException { out.beginObject(); out.name("isbn").value(book.getIsbn()); out.name("title").value(book.getTitle()); out.name("authors").beginArray(); for (final Author author : book.getAuthors()) { out.beginObject(); out.name("id").value(author.getId()); out.name("name").value(author.getName()); out.endObject(); } out.endArray(); out.endObject(); }

@Override public Book read(final JsonReader in) throws IOException { final Book book = new Book(); in.beginObject(); while (in.hasNext()) { switch (in.nextName()) { case "isbn": book.setIsbn(in.nextString()); break; case "title": book.setTitle(in.nextString()); break; case "authors": in.beginArray(); final List authors = new ArrayList<>(); while (in.hasNext()) { in.beginObject(); final Author author = new Author(); while (in.hasNext()) { switch (in.nextName()) { case "id": author.setId(in.nextInt()); break; case "name": author.setName(in.nextString()); break; } } authors.add(author); in.endObject(); } book.setAuthors(authors.toArray(new Author[authors.size()])); in.endArray(); break; } } in.endObject(); return book; }

summary

TypeAdapter can operate on serialization and deserialization between JSON and Java objects through the above methods. In fact, when resolving the serialization and deserialization of built-in objects, we can also operate through JsonDeserializer or JsonSerializer. The serialization process is as follows:

@Override public JsonElement serialize(final Book book, final Type typeOfSrc, final JsonSerializationContext context) { final JsonObject jsonObject = new JsonObject(); jsonObject.addProperty("isbn", book.getIsbn()); jsonObject.addProperty("title", book.getTitle()); final JsonElement jsonAuthros = context.serialize(book.getAuthors()); jsonObject.add("authors", jsonAuthros); return jsonObject; }

Here, the context object provided by JsonSerializationContext is directly parsed, which to some extent provides the consistency of JSON object serialization (deserialization).

< the above content is reprinted, and the following is the original author's information >

By Anthony
Links: https://www.jianshu.com/p/8cc857583ff4
Source: Jianshu

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