JsonReader (lottie API)

java.lang.Object
- com.airbnb.lottie.parser.moshi.JsonReader

All Implemented Interfaces:: java.io.Closeable, java.lang.AutoCloseable

public abstract class JsonReader
extends java.lang.Object
implements java.io.Closeable

Reads a JSON (RFC 7159) encoded value as a stream of tokens. This stream includes both literal values (strings, numbers, booleans, and nulls) as well as the begin and end delimiters of objects and arrays. The tokens are traversed in depth-first order, the same order that they appear in the JSON document. Within JSON objects, name/value pairs are represented by a single token.

Parsing JSON

To create a recursive descent parser for your own JSON streams, first create an entry point method that creates a JsonReader.

Next, create handler methods for each structure in your JSON text. You'll need a method for each object type and for each array type.

Within array handling methods, first call beginArray() to consume the array's opening bracket. Then create a while loop that accumulates values, terminating when hasNext() is false. Finally, read the array's closing bracket by calling endArray().
Within object handling methods, first call beginObject() to consume the object's opening brace. Then create a while loop that assigns values to local variables based on their name. This loop should terminate when hasNext() is false. Finally, read the object's closing brace by calling endObject().

When a nested object or array is encountered, delegate to the corresponding handler method.

When an unknown name is encountered, strict parsers should fail with an exception. Lenient parsers should call skipValue() to recursively skip the value's nested tokens, which may otherwise conflict.

If a value may be null, you should first check using peek(). Null literals can be consumed using either #nextNull() or skipValue().

Example

Suppose we'd like to parse a stream of messages such as the following:

 
 [
   {
     "id": 912345678901,
     "text": "How do I read a JSON stream in Java?",
     "geo": null,
     "user": {
       "name": "json_newb",
       "followers_count": 41
      }
   },
   {
     "id": 912345678902,
     "text": "@json_newb just use JsonReader!",
     "geo": [50.454722, -104.606667],
     "user": {
       "name": "jesse",
       "followers_count": 2
     }
   }
 ]

This code implements the parser for the above structure:

   

   public List<Message> readJsonStream(BufferedSource source) throws IOException {
     JsonReader reader = JsonReader.of(source);
     try {
       return readMessagesArray(reader);
     } finally {
       reader.close();
     }
   }

   public List<Message> readMessagesArray(JsonReader reader) throws IOException {
     List<Message> messages = new ArrayList<Message>();

     reader.beginArray();
     while (reader.hasNext()) {
       messages.add(readMessage(reader));
     }
     reader.endArray();
     return messages;
   }

   public Message readMessage(JsonReader reader) throws IOException {
     long id = -1;
     String text = null;
     User user = null;
     List<Double> geo = null;

     reader.beginObject();
     while (reader.hasNext()) {
       String name = reader.nextName();
       if (name.equals("id")) {
         id = reader.nextLong();
       } else if (name.equals("text")) {
         text = reader.nextString();
       } else if (name.equals("geo") && reader.peek() != Token.NULL) {
         geo = readDoublesArray(reader);
       } else if (name.equals("user")) {
         user = readUser(reader);
       } else {
         reader.skipValue();
       }
     }
     reader.endObject();
     return new Message(id, text, user, geo);
   }

   public List<Double> readDoublesArray(JsonReader reader) throws IOException {
     List<Double> doubles = new ArrayList<Double>();

     reader.beginArray();
     while (reader.hasNext()) {
       doubles.add(reader.nextDouble());
     }
     reader.endArray();
     return doubles;
   }

   public User readUser(JsonReader reader) throws IOException {
     String username = null;
     int followersCount = -1;

     reader.beginObject();
     while (reader.hasNext()) {
       String name = reader.nextName();
       if (name.equals("name")) {
         username = reader.nextString();
       } else if (name.equals("followers_count")) {
         followersCount = reader.nextInt();
       } else {
         reader.skipValue();
       }
     }
     reader.endObject();
     return new User(username, followersCount);
   }

Number Handling

This reader permits numeric values to be read as strings and string values to be read as numbers. For example, both elements of the JSON array [1, "1"] may be read using either nextInt() or nextString(). This behavior is intended to prevent lossy numeric conversions: double is JavaScript's only numeric type and very large values like 9007199254740993 cannot be represented exactly on that platform. To minimize precision loss, extremely large values should be written and read as strings in JSON.

Each JsonReader may be used to read a single JSON stream. Instances of this class are not thread safe.

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`static class`	`JsonReader.Options` A set of strings to be chosen with `selectName(com.airbnb.lottie.parser.moshi.JsonReader.Options)` or `#selectString`.
`static class`	`JsonReader.Token` A structure, name, or value type in a JSON-encoded string.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`abstract void`	`beginArray()` Consumes the next token from the JSON stream and asserts that it is the beginning of a new array.
`abstract void`	`beginObject()` Consumes the next token from the JSON stream and asserts that it is the beginning of a new object.
`abstract void`	`endArray()` Consumes the next token from the JSON stream and asserts that it is the end of the current array.
`abstract void`	`endObject()` Consumes the next token from the JSON stream and asserts that it is the end of the current object.
`java.lang.String`	`getPath()` Returns a JsonPath to the current location in the JSON value.
`abstract boolean`	`hasNext()` Returns true if the current array or object has another element.
`abstract boolean`	`nextBoolean()` Returns the boolean value of the next token, consuming it.
`abstract double`	`nextDouble()` Returns the double value of the next token, consuming it.
`abstract int`	`nextInt()` Returns the int value of the next token, consuming it.
`abstract java.lang.String`	`nextName()` Returns the next token, a property name, and consumes it.
`abstract java.lang.String`	`nextString()` Returns the string value of the next token, consuming it.
`static JsonReader`	`of(BufferedSource source)` Returns a new instance that reads UTF-8 encoded JSON from `source`.
`abstract JsonReader.Token`	`peek()` Returns the type of the next token without consuming it.
`abstract int`	`selectName(JsonReader.Options options)` If the next token is a property name that's in `options`, this consumes it and returns its index.
`abstract void`	`skipName()` Skips the next token, consuming it.
`abstract void`	`skipValue()` Skips the next value recursively.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.io.Closeable
close

- Method Detail
  - of
```
public static JsonReader of(BufferedSource source)
```
    Returns a new instance that reads UTF-8 encoded JSON from source.
  - beginArray
```
public abstract void beginArray()
                         throws java.io.IOException
```
    Consumes the next token from the JSON stream and asserts that it is the beginning of a new array.
    
    Throws:
    
    java.io.IOException
  - endArray
```
public abstract void endArray()
                       throws java.io.IOException
```
    Consumes the next token from the JSON stream and asserts that it is the end of the current array.
    
    Throws:
    
    java.io.IOException
  - beginObject
```
public abstract void beginObject()
                          throws java.io.IOException
```
    Consumes the next token from the JSON stream and asserts that it is the beginning of a new object.
    
    Throws:
    
    java.io.IOException
  - endObject
```
public abstract void endObject()
                        throws java.io.IOException
```
    Consumes the next token from the JSON stream and asserts that it is the end of the current object.
    
    Throws:
    
    java.io.IOException
  - hasNext
```
public abstract boolean hasNext()
                         throws java.io.IOException
```
    Returns true if the current array or object has another element.
    
    Throws:
    
    java.io.IOException
  - peek
```
public abstract JsonReader.Token peek()
                               throws java.io.IOException
```
    Returns the type of the next token without consuming it.
    
    Throws:
    
    java.io.IOException
  - nextName
```
public abstract java.lang.String nextName()
                                   throws java.io.IOException
```
    Returns the next token, a property name, and consumes it.
    
    Throws:
    
    JsonDataException - if the next token in the stream is not a property name.
    
    java.io.IOException
  - selectName
```
public abstract int selectName(JsonReader.Options options)
                        throws java.io.IOException
```
    If the next token is a property name that's in options, this consumes it and returns its index. Otherwise this returns -1 and no name is consumed.
    
    Throws:
    
    java.io.IOException
  - skipName
```
public abstract void skipName()
                       throws java.io.IOException
```
    Skips the next token, consuming it. This method is intended for use when the JSON token stream contains unrecognized or unhandled names.
    This throws a JsonDataException if this parser has been configured to fail on unknown names.
    
    Throws:
    
    java.io.IOException
  - nextString
```
public abstract java.lang.String nextString()
                                     throws java.io.IOException
```
    Returns the string value of the next token, consuming it. If the next token is a number, this method will return its string form.
    
    Throws:
    
    JsonDataException - if the next token is not a string or if this reader is closed.
    
    java.io.IOException
  - nextBoolean
```
public abstract boolean nextBoolean()
                             throws java.io.IOException
```
    Returns the boolean value of the next token, consuming it.
    
    Throws:
    
    JsonDataException - if the next token is not a boolean or if this reader is closed.
    
    java.io.IOException
  - nextDouble
```
public abstract double nextDouble()
                           throws java.io.IOException
```
    Returns the double value of the next token, consuming it. If the next token is a string, this method will attempt to parse it as a double using Double.parseDouble(String).
    
    Throws:
    
    JsonDataException - if the next token is not a literal value, or if the next literal value cannot be parsed as a double, or is non-finite.
    
    java.io.IOException
  - nextInt
```
public abstract int nextInt()
                     throws java.io.IOException
```
    Returns the int value of the next token, consuming it. If the next token is a string, this method will attempt to parse it as an int. If the next token's numeric value cannot be exactly represented by a Java int, this method throws.
    
    Throws:
    
    JsonDataException - if the next token is not a literal value, if the next literal value cannot be parsed as a number, or exactly represented as an int.
    
    java.io.IOException
  - skipValue
```
public abstract void skipValue()
                        throws java.io.IOException
```
    Skips the next value recursively. If it is an object or array, all nested elements are skipped. This method is intended for use when the JSON token stream contains unrecognized or unhandled values.
    This throws a JsonDataException if this parser has been configured to fail on unknown values.
    
    Throws:
    
    java.io.IOException
  - getPath
```
public final java.lang.String getPath()
```
    Returns a JsonPath to the current location in the JSON value.

Class JsonReader

Parsing JSON

Example

Number Handling

Nested Class Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.io.Closeable

Method Detail

of

beginArray

endArray

beginObject

endObject

hasNext

peek

nextName

selectName

skipName

nextString

nextBoolean

nextDouble

nextInt

skipValue

getPath