com.google.flatbuffers

Class FlatBufferBuilder

java.lang.Object

com.google.flatbuffers.FlatBufferBuilder

public class FlatBufferBuilder
extends Object

Class that helps you build a FlatBuffer. See the section "Use in Java/C#" in the main FlatBuffers documentation.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	FlatBufferBuilder.ByteBufferFactory An interface that provides a user of the FlatBufferBuilder class the ability to specify the method in which the internal buffer gets allocated.
static class	FlatBufferBuilder.HeapByteBufferFactory An implementation of the ByteBufferFactory interface that is used when one is not provided by the user.

Constructor Summary

Constructors

Constructor and Description
FlatBufferBuilder() Start with a buffer of 1KiB, then grow as required.
FlatBufferBuilder(ByteBuffer existing_bb) Alternative constructor allowing reuse of ByteBuffers.
FlatBufferBuilder(ByteBuffer existing_bb, FlatBufferBuilder.ByteBufferFactory bb_factory) Alternative constructor allowing reuse of ByteBuffers.
FlatBufferBuilder(int initial_size) Start with a buffer of size `initial_size`, then grow as required.
FlatBufferBuilder(int initial_size, FlatBufferBuilder.ByteBufferFactory bb_factory) Start with a buffer of size `initial_size`, then grow as required.

Method Summary

Methods

Modifier and Type	Method and Description
void	addBoolean(boolean x) Add a `boolean` to the buffer, properly aligned, and grows the buffer (if necessary).
void	addBoolean(int o, boolean x, boolean d) Add a `boolean` to a table at `o` into its vtable, with value `x` and default `d`.
void	addByte(byte x) Add a `byte` to the buffer, properly aligned, and grows the buffer (if necessary).
void	addByte(int o, byte x, int d) Add a `byte` to a table at `o` into its vtable, with value `x` and default `d`.
void	addDouble(double x) Add a `double` to the buffer, properly aligned, and grows the buffer (if necessary).
void	addDouble(int o, double x, double d) Add a `double` to a table at `o` into its vtable, with value `x` and default `d`.
void	addFloat(float x) Add a `float` to the buffer, properly aligned, and grows the buffer (if necessary).
void	addFloat(int o, float x, double d) Add a `float` to a table at `o` into its vtable, with value `x` and default `d`.
void	addInt(int x) Add an `int` to the buffer, properly aligned, and grows the buffer (if necessary).
void	addInt(int o, int x, int d) Add an `int` to a table at `o` into its vtable, with value `x` and default `d`.
void	addLong(int o, long x, long d) Add a `long` to a table at `o` into its vtable, with value `x` and default `d`.
void	addLong(long x) Add a `long` to the buffer, properly aligned, and grows the buffer (if necessary).
void	addOffset(int off) Adds on offset, relative to where it will be written.
void	addOffset(int o, int x, int d) Add an `offset` to a table at `o` into its vtable, with value `x` and default `d`.
void	addShort(int o, short x, int d) Add a `short` to a table at `o` into its vtable, with value `x` and default `d`.
void	addShort(short x) Add a `short` to the buffer, properly aligned, and grows the buffer (if necessary).
void	addStruct(int voffset, int x, int d) Add a struct to the table.
void	clear() Reset the FlatBufferBuilder by purging all data that it holds.
int	createByteVector(byte[] arr) Create a byte array in the buffer.
<T extends Table> int	createSortedVectorOfTables(T obj, int[] offsets) Create a vector of sorted by the key tables.
int	createString(ByteBuffer s) Create a string in the buffer from an already encoded UTF-8 string in a ByteBuffer.
int	createString(CharSequence s) Encode the string `s` in the buffer using UTF-8.
ByteBuffer	createUnintializedVector(int elem_size, int num_elems, int alignment) Create a new array/vector and return a ByteBuffer to be filled later.
int	createVectorOfTables(int[] offsets) Create a vector of tables.
ByteBuffer	dataBuffer() Get the ByteBuffer representing the FlatBuffer.
int	endObject() Finish off writing the object that is under construction.
int	endVector() Finish off the creation of an array and all its elements.
void	finish(int root_table) Finalize a buffer, pointing to the given `root_table`.
void	finish(int root_table, String file_identifier) Finalize a buffer, pointing to the given `root_table`.
void	finished() Should not be accessing the final buffer before it is finished.
FlatBufferBuilder	forceDefaults(boolean forceDefaults) In order to save space, fields that are set to their default value don't get serialized into the buffer.
FlatBufferBuilder	init(ByteBuffer existing_bb, FlatBufferBuilder.ByteBufferFactory bb_factory) Alternative initializer that allows reusing this object on an existing `ByteBuffer`.
void	Nested(int obj) Structures are always stored inline, they need to be created right where they're used.
void	notNested() Should not be creating any other object, string or vector while an object is being constructed.
int	offset() Offset relative to the end of the buffer.
void	pad(int byte_size) Add zero valued bytes to prepare a new entry to be added.
void	prep(int size, int additional_bytes) Prepare to write an element of `size` after `additional_bytes` have been written, e.g.
void	putBoolean(boolean x) Add a `boolean` to the buffer, backwards from the current location.
void	putByte(byte x) Add a `byte` to the buffer, backwards from the current location.
void	putDouble(double x) Add a `double` to the buffer, backwards from the current location.
void	putFloat(float x) Add a `float` to the buffer, backwards from the current location.
void	putInt(int x) Add an `int` to the buffer, backwards from the current location.
void	putLong(long x) Add a `long` to the buffer, backwards from the current location.
void	putShort(short x) Add a `short` to the buffer, backwards from the current location.
void	required(int table, int field) Checks that a required field has been set in a given table that has just been constructed.
byte[]	sizedByteArray() A utility function to copy and return the ByteBuffer data as a `byte[]`.
byte[]	sizedByteArray(int start, int length) A utility function to copy and return the ByteBuffer data from `start` to `start` + `length` as a `byte[]`.
InputStream	sizedInputStream() A utility function to return an InputStream to the ByteBuffer data
void	slot(int voffset) Set the current vtable at `voffset` to the current location in the buffer.
void	startObject(int numfields) Start encoding a new object in the buffer.
void	startVector(int elem_size, int num_elems, int alignment) Start a new array/vector of objects.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FlatBufferBuilder

public FlatBufferBuilder(int initial_size,
                 FlatBufferBuilder.ByteBufferFactory bb_factory)

Start with a buffer of size `initial_size`, then grow as required.

Parameters:

initial_size - The initial size of the internal buffer to use.

bb_factory - The factory to be used for allocating the internal buffer

FlatBufferBuilder

public FlatBufferBuilder(int initial_size)

Start with a buffer of size `initial_size`, then grow as required.

Parameters:

initial_size - The initial size of the internal buffer to use.

FlatBufferBuilder

public FlatBufferBuilder()

Start with a buffer of 1KiB, then grow as required.

FlatBufferBuilder

public FlatBufferBuilder(ByteBuffer existing_bb,
                 FlatBufferBuilder.ByteBufferFactory bb_factory)

Alternative constructor allowing reuse of ByteBuffers. The builder can still grow the buffer as necessary. User classes should make sure to call dataBuffer() to obtain the resulting encoded message.

Parameters:

existing_bb - The byte buffer to reuse.

bb_factory - The factory to be used for allocating a new internal buffer if the existing buffer needs to grow

FlatBufferBuilder

public FlatBufferBuilder(ByteBuffer existing_bb)

Alternative constructor allowing reuse of ByteBuffers. The builder can still grow the buffer as necessary. User classes should make sure to call dataBuffer() to obtain the resulting encoded message.

Parameters:

existing_bb - The byte buffer to reuse.

Method Detail

init

public FlatBufferBuilder init(ByteBuffer existing_bb,
                     FlatBufferBuilder.ByteBufferFactory bb_factory)

Alternative initializer that allows reusing this object on an existing `ByteBuffer`. This method resets the builder's internal state, but keeps objects that have been allocated for temporary storage.

Parameters:

existing_bb - The byte buffer to reuse.

bb_factory - The factory to be used for allocating a new internal buffer if the existing buffer needs to grow

Returns:

Returns `this`.

clear

public void clear()

Reset the FlatBufferBuilder by purging all data that it holds.

offset

public int offset()

Offset relative to the end of the buffer.

Returns:

Offset relative to the end of the buffer.

pad

public void pad(int byte_size)

Add zero valued bytes to prepare a new entry to be added.

Parameters:

byte_size - Number of bytes to add.

prep

public void prep(int size,
        int additional_bytes)

Prepare to write an element of `size` after `additional_bytes` have been written, e.g. if you write a string, you need to align such the int length field is aligned to Constants.SIZEOF_INT, and the string data follows it directly. If all you need to do is alignment, `additional_bytes` will be 0.

Parameters:

size - This is the of the new element to write.

additional_bytes - The padding size.

putBoolean

public void putBoolean(boolean x)

Add a `boolean` to the buffer, backwards from the current location. Doesn't align nor check for space.

Parameters:

x - A `boolean` to put into the buffer.

putByte

public void putByte(byte x)

Add a `byte` to the buffer, backwards from the current location. Doesn't align nor check for space.

Parameters:

x - A `byte` to put into the buffer.

putShort

public void putShort(short x)

Add a `short` to the buffer, backwards from the current location. Doesn't align nor check for space.

Parameters:

x - A `short` to put into the buffer.

putInt

public void putInt(int x)

Add an `int` to the buffer, backwards from the current location. Doesn't align nor check for space.

Parameters:

x - An `int` to put into the buffer.

putLong

public void putLong(long x)

Add a `long` to the buffer, backwards from the current location. Doesn't align nor check for space.

Parameters:

x - A `long` to put into the buffer.

putFloat

public void putFloat(float x)

Add a `float` to the buffer, backwards from the current location. Doesn't align nor check for space.

Parameters:

x - A `float` to put into the buffer.

putDouble

public void putDouble(double x)

Add a `double` to the buffer, backwards from the current location. Doesn't align nor check for space.

Parameters:

x - A `double` to put into the buffer.

addBoolean

public void addBoolean(boolean x)

Add a `boolean` to the buffer, properly aligned, and grows the buffer (if necessary).

Parameters:

x - A `boolean` to put into the buffer.

addByte

public void addByte(byte x)

Add a `byte` to the buffer, properly aligned, and grows the buffer (if necessary).

Parameters:

x - A `byte` to put into the buffer.

addShort

public void addShort(short x)

Add a `short` to the buffer, properly aligned, and grows the buffer (if necessary).

Parameters:

x - A `short` to put into the buffer.

addInt

public void addInt(int x)

Add an `int` to the buffer, properly aligned, and grows the buffer (if necessary).

Parameters:

x - An `int` to put into the buffer.

addLong

public void addLong(long x)

Add a `long` to the buffer, properly aligned, and grows the buffer (if necessary).

Parameters:

x - A `long` to put into the buffer.

addFloat

public void addFloat(float x)

Add a `float` to the buffer, properly aligned, and grows the buffer (if necessary).

Parameters:

x - A `float` to put into the buffer.

addDouble

public void addDouble(double x)

Add a `double` to the buffer, properly aligned, and grows the buffer (if necessary).

Parameters:

x - A `double` to put into the buffer.

addOffset

public void addOffset(int off)

Adds on offset, relative to where it will be written.

Parameters:

off - The offset to add.

startVector

public void startVector(int elem_size,
               int num_elems,
               int alignment)

Start a new array/vector of objects. Users usually will not call this directly. The `FlatBuffers` compiler will create a start/end method for vector types in generated code.

The expected sequence of calls is:

1. Start the array using this method.
2. Call addOffset(int) `num_elems` number of times to set the offset of each element in the array.
3. Call endVector() to retrieve the offset of the array.

For example, to create an array of strings, do:

// Need 10 strings
 FlatBufferBuilder builder = new FlatBufferBuilder(existingBuffer);
 int[] offsets = new int[10];

 for (int i = 0; i < 10; i++) {
   offsets[i] = fbb.createString(" " + i);
 }

 // Have the strings in the buffer, but don't have a vector.
 // Add a vector that references the newly created strings:
 builder.startVector(4, offsets.length, 4);

 // Add each string to the newly created vector
 // The strings are added in reverse order since the buffer
 // is filled in back to front
 for (int i = offsets.length - 1; i >= 0; i--) {
   builder.addOffset(offsets[i]);
 }

 // Finish off the vector
 int offsetOfTheVector = fbb.endVector();
 

Parameters:

elem_size - The size of each element in the array.

num_elems - The number of elements in the array.

alignment - The alignment of the array.

endVector

public int endVector()

Finish off the creation of an array and all its elements. The array must be created with startVector(int, int, int).

Returns:

The offset at which the newly created array starts.

See Also:

startVector(int, int, int)

createUnintializedVector

public ByteBuffer createUnintializedVector(int elem_size,
                                  int num_elems,
                                  int alignment)

Create a new array/vector and return a ByteBuffer to be filled later. Call endVector() after this method to get an offset to the beginning of vector.

Parameters:

elem_size - the size of each element in bytes.

num_elems - number of elements in the vector.

alignment - byte alignment.

Returns:

ByteBuffer with position and limit set to the space allocated for the array.

createVectorOfTables

public int createVectorOfTables(int[] offsets)

Create a vector of tables.

Parameters:

offsets - Offsets of the tables.

Returns:

Returns offset of the vector.

createSortedVectorOfTables

public <T extends Table> int createSortedVectorOfTables(T obj,
                                               int[] offsets)

Create a vector of sorted by the key tables.

Parameters:

obj - Instance of the table subclass.

offsets - Offsets of the tables.

Returns:

Returns offset of the sorted vector.

createString

public int createString(CharSequence s)

Encode the string `s` in the buffer using UTF-8. If s is already a CharBuffer, this method is allocation free.

Parameters:

s - The string to encode.

Returns:

The offset in the buffer where the encoded string starts.

createString

public int createString(ByteBuffer s)

Create a string in the buffer from an already encoded UTF-8 string in a ByteBuffer.

Parameters:

s - An already encoded UTF-8 string as a `ByteBuffer`.

Returns:

The offset in the buffer where the encoded string starts.

createByteVector

public int createByteVector(byte[] arr)

Create a byte array in the buffer.

Parameters:

arr - A source array with data

Returns:

The offset in the buffer where the encoded array starts.

finished

public void finished()

Should not be accessing the final buffer before it is finished.

notNested

public void notNested()

Should not be creating any other object, string or vector while an object is being constructed.

Nested

public void Nested(int obj)

Structures are always stored inline, they need to be created right where they're used. You'll get this assertion failure if you created it elsewhere.

Parameters:

obj - The offset of the created object.

startObject

public void startObject(int numfields)

Start encoding a new object in the buffer. Users will not usually need to call this directly. The `FlatBuffers` compiler will generate helper methods that call this method internally.

For example, using the "Monster" code found on the "landing page". An object of type `Monster` can be created using the following code:

int testArrayOfString = Monster.createTestarrayofstringVector(fbb, new int[] {
   fbb.createString("test1"),
   fbb.createString("test2")
 });

 Monster.startMonster(fbb);
 Monster.addPos(fbb, Vec3.createVec3(fbb, 1.0f, 2.0f, 3.0f, 3.0,
   Color.Green, (short)5, (byte)6));
 Monster.addHp(fbb, (short)80);
 Monster.addName(fbb, str);
 Monster.addInventory(fbb, inv);
 Monster.addTestType(fbb, (byte)Any.Monster);
 Monster.addTest(fbb, mon2);
 Monster.addTest4(fbb, test4);
 Monster.addTestarrayofstring(fbb, testArrayOfString);
 int mon = Monster.endMonster(fbb);
 

Here:

• The call to `Monster#startMonster(FlatBufferBuilder)` will call this method with the right number of fields set.
• `Monster#endMonster(FlatBufferBuilder)` will ensure endObject() is called.

It's not recommended to call this method directly. If it's called manually, you must ensure to audit all calls to it whenever fields are added or removed from your schema. This is automatically done by the code generated by the `FlatBuffers` compiler.

Parameters:

numfields - The number of fields found in this object.

addBoolean

public void addBoolean(int o,
              boolean x,
              boolean d)

Add a `boolean` to a table at `o` into its vtable, with value `x` and default `d`.

Parameters:

o - The index into the vtable.

x - A `boolean` to put into the buffer, depending on how defaults are handled. If `force_defaults` is `false`, compare `x` against the default value `d`. If `x` contains the default value, it can be skipped.

d - A `boolean` default value to compare against when `force_defaults` is `false`.

addByte

public void addByte(int o,
           byte x,
           int d)

Add a `byte` to a table at `o` into its vtable, with value `x` and default `d`.

Parameters:

o - The index into the vtable.

x - A `byte` to put into the buffer, depending on how defaults are handled. If `force_defaults` is `false`, compare `x` against the default value `d`. If `x` contains the default value, it can be skipped.

d - A `byte` default value to compare against when `force_defaults` is `false`.

addShort

public void addShort(int o,
            short x,
            int d)

Add a `short` to a table at `o` into its vtable, with value `x` and default `d`.

Parameters:

o - The index into the vtable.

x - A `short` to put into the buffer, depending on how defaults are handled. If `force_defaults` is `false`, compare `x` against the default value `d`. If `x` contains the default value, it can be skipped.

d - A `short` default value to compare against when `force_defaults` is `false`.

addInt

public void addInt(int o,
          int x,
          int d)

Add an `int` to a table at `o` into its vtable, with value `x` and default `d`.

Parameters:

o - The index into the vtable.

x - An `int` to put into the buffer, depending on how defaults are handled. If `force_defaults` is `false`, compare `x` against the default value `d`. If `x` contains the default value, it can be skipped.

d - An `int` default value to compare against when `force_defaults` is `false`.

addLong

public void addLong(int o,
           long x,
           long d)

Add a `long` to a table at `o` into its vtable, with value `x` and default `d`.

Parameters:

o - The index into the vtable.

x - A `long` to put into the buffer, depending on how defaults are handled. If `force_defaults` is `false`, compare `x` against the default value `d`. If `x` contains the default value, it can be skipped.

d - A `long` default value to compare against when `force_defaults` is `false`.

addFloat

public void addFloat(int o,
            float x,
            double d)

Add a `float` to a table at `o` into its vtable, with value `x` and default `d`.

Parameters:

o - The index into the vtable.

x - A `float` to put into the buffer, depending on how defaults are handled. If `force_defaults` is `false`, compare `x` against the default value `d`. If `x` contains the default value, it can be skipped.

d - A `float` default value to compare against when `force_defaults` is `false`.

addDouble

public void addDouble(int o,
             double x,
             double d)

Add a `double` to a table at `o` into its vtable, with value `x` and default `d`.

Parameters:

o - The index into the vtable.

x - A `double` to put into the buffer, depending on how defaults are handled. If `force_defaults` is `false`, compare `x` against the default value `d`. If `x` contains the default value, it can be skipped.

d - A `double` default value to compare against when `force_defaults` is `false`.

addOffset

public void addOffset(int o,
             int x,
             int d)

Add an `offset` to a table at `o` into its vtable, with value `x` and default `d`.

Parameters:

o - The index into the vtable.

x - An `offset` to put into the buffer, depending on how defaults are handled. If `force_defaults` is `false`, compare `x` against the default value `d`. If `x` contains the default value, it can be skipped.

d - An `offset` default value to compare against when `force_defaults` is `false`.

addStruct

public void addStruct(int voffset,
             int x,
             int d)

Add a struct to the table. Structs are stored inline, so nothing additional is being added.

Parameters:

voffset - The index into the vtable.

x - The offset of the created struct.

d - The default value is always `0`.

slot

public void slot(int voffset)

Set the current vtable at `voffset` to the current location in the buffer.

Parameters:

voffset - The index into the vtable to store the offset relative to the end of the buffer.

endObject

public int endObject()

Finish off writing the object that is under construction.

Returns:

The offset to the object inside dataBuffer().

See Also:

startObject(int)

required

public void required(int table,
            int field)

Checks that a required field has been set in a given table that has just been constructed.

Parameters:

table - The offset to the start of the table from the `ByteBuffer` capacity.

field - The offset to the field in the vtable.

finish

public void finish(int root_table)

Finalize a buffer, pointing to the given `root_table`.

Parameters:

root_table - An offset to be added to the buffer.

finish

public void finish(int root_table,
          String file_identifier)

Finalize a buffer, pointing to the given `root_table`.

Parameters:

root_table - An offset to be added to the buffer.

file_identifier - A FlatBuffer file identifier to be added to the buffer before `root_table`.

forceDefaults

public FlatBufferBuilder forceDefaults(boolean forceDefaults)

In order to save space, fields that are set to their default value don't get serialized into the buffer. Forcing defaults provides a way to manually disable this optimization.

Parameters:

forceDefaults - When set to `true`, always serializes default values.

Returns:

Returns `this`.

dataBuffer

public ByteBuffer dataBuffer()

Get the ByteBuffer representing the FlatBuffer. Only call this after you've called `finish()`. The actual data starts at the ByteBuffer's current position, not necessarily at `0`.

Returns:

The ByteBuffer representing the FlatBuffer

sizedByteArray

public byte[] sizedByteArray(int start,
                    int length)

A utility function to copy and return the ByteBuffer data from `start` to `start` + `length` as a `byte[]`.

Parameters:

start - Start copying at this offset.

length - How many bytes to copy.

Returns:

A range copy of the data buffer.

Throws:

IndexOutOfBoundsException - If the range of bytes is ouf of bound.

sizedByteArray

public byte[] sizedByteArray()

A utility function to copy and return the ByteBuffer data as a `byte[]`.

Returns:

A full copy of the data buffer.

sizedInputStream

public InputStream sizedInputStream()

A utility function to return an InputStream to the ByteBuffer data

Returns:

An InputStream that starts at the beginning of the ByteBuffer data and can read to the end of it.