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先来看一下 FlatBuffers 项目已经为我们提供了什么,而我们在将 FlatBuffers 用到我们的项目中时又需要做什么的整体流程。如下图:

在Android中使用FlatBuffers(上篇)-LMLPHP

在使用 FlatBuffers 时,我们需要以特殊的格式定义我们的结构化数据,保存为 .fbs 文件。FlatBuffers 项目为我们提供了编译器,可用于将 .fbs 文件编译为Java文件,C++文件等,以用于我们的项目。FlatBuffers 编译器在我们的开发机,比如Ubuntu,Mac上运行。这些源代码文件是基于 FlatBuffers 提供的Java库生成的,同时我们也需要利用这个Java库的一些接口来序列化或解析数据。

我们将 FlatBuffers 编译器生成的Java文件及 FlatBuffers 的Java库导入我们的项目,就可以用 FlatBuffers 来对我们的结构化数据执行序列化和反序列化了。尽管每次手动执行 FlatBuffers 编译器生成Java文件非常麻烦,但不像 Protocol Buffers 那样,当前还没有Google官方提供的gradle插件可用。不过,我们这边开发了一个简单的 FlatBuffers gradle插件,后面会简单介绍一下,欢迎大家使用。

接下来我们更详细地看一下上面流程中的各个部分。

下载、编译 FlatBuffers 编译器

我们可以在如下位置:

https://github.com/google/flatbuffers/releases

获取官方发布的打包好的版本。针对Windows平台有编译好的可执行安装文件,对其它平台还是打包的源文件。我们也可以指向clone repo的代码,进行手动编译。这里我们从GitHub上clone代码并手动编译编译器:

$ git clone https://github.com/google/flatbuffers.git
Cloning into 'flatbuffers'...
remote: Counting objects: 7340, done.
remote: Compressing objects: 100% (46/46), done.
remote: Total 7340 (delta 16), reused 0 (delta 0), pack-reused 7290
Receiving objects: 100% (7340/7340), 3.64 MiB | 115.00 KiB/s, done.
Resolving deltas: 100% (4692/4692), done.
Checking connectivity... done.

下载代码之后,我们需要用cmake工具来为flatbuffers生成Makefile文件并编译:

$ cd flatbuffers/
$ cmake CMakeLists.txt
-- The C compiler identification is AppleClang 7.3.0.7030031
-- The CXX compiler identification is AppleClang 7.3.0.7030031
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc
-- Check for working C compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++
-- Check for working CXX compiler: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/netease/Projects/OpenSource/flatbuffers
$ make && make install

安装之后执行如下命令以确认已经装好:

$ flatc --version
flatc version 1.4.0 (Dec 7 2016)

flatc没有为我们提供 --help 选项,不过加了错误的参数时这个工具会为我们展示详细的用法:

$ flatc --help
flatc: unknown commandline argument: --help
usage: flatc [OPTION]... FILE... [-- FILE...]
--binary -b Generate wire format binaries for any data definitions.
--json -t Generate text output for any data definitions.
--cpp -c Generate C++ headers for tables/structs.
--go -g Generate Go files for tables/structs.
--java -j Generate Java classes for tables/structs.
--js -s Generate JavaScript code for tables/structs.
--csharp -n Generate C# classes for tables/structs.
--python -p Generate Python files for tables/structs.
--php Generate PHP files for tables/structs.
-o PATH Prefix PATH to all generated files.
-I PATH Search for includes in the specified path.
-M Print make rules for generated files.
--version Print the version number of flatc and exit.
--strict-json Strict JSON: field names must be / will be quoted,
no trailing commas in tables/vectors.
--allow-non-utf8 Pass non-UTF-8 input through parser and emit nonstandard
\x escapes in JSON. (Default is to raise parse error on
non-UTF-8 input.)
--defaults-json Output fields whose value is the default when
writing JSON
--unknown-json Allow fields in JSON that are not defined in the
schema. These fields will be discared when generating
binaries.
--no-prefix Don't prefix enum values with the enum type in C++.
--scoped-enums Use C++11 style scoped and strongly typed enums.
also implies --no-prefix.
--gen-includes (deprecated), this is the default behavior.
If the original behavior is required (no include
statements) use --no-includes.
--no-includes Don't generate include statements for included
schemas the generated file depends on (C++).
--gen-mutable Generate accessors that can mutate buffers in-place.
--gen-onefile Generate single output file for C#.
--gen-name-strings Generate type name functions for C++.
--escape-proto-ids Disable appending '_' in namespaces names.
--gen-object-api Generate an additional object-based API.
--cpp-ptr-type T Set object API pointer type (default std::unique_ptr)
--raw-binary Allow binaries without file_indentifier to be read.
This may crash flatc given a mismatched schema.
--proto Input is a .proto, translate to .fbs.
--schema Serialize schemas instead of JSON (use with -b)
--conform FILE Specify a schema the following schemas should be
an evolution of. Gives errors if not.
--conform-includes Include path for the schema given with --conform
PATH
FILEs may be schemas, or JSON files (conforming to preceding schema)
FILEs after the -- must be binary flatbuffer format files.
Output files are named using the base file name of the input,
and written to the current directory or the path given by -o.
example: flatc -c -b schema1.fbs schema2.fbs data.json

创建 .fbs 文件

flatc支持将为 Protocol Buffers 编写的 .proto 文件转换为 .fbs 文件,如:

$ ls
addressbook.proto
$ flatc --proto addressbook.proto
$ ls -l
total 16
-rw-r--r-- 1 netease staff 431 12 7 17:21 addressbook.fbs
-rw-r--r--@ 1 netease staff 486 12 1 15:18 addressbook.proto

Protocol Buffers 消息文件中的一些写法,FlatBuffers 编译器还不能很好的支持,如option java_package,option java_outer_classname,和嵌套类。这里我们基于 FlatBuffers 编译器转换的 .proto 文件来获得我们的 .fbs 文件:

// Generated from addressbook.proto

namespace com.example.tutorial;

enum PhoneType : int {
MOBILE = 0,
HOME = 1,
WORK = 2,
} namespace com.example.tutorial; table Person {
name:string (required);
id:int;
email:string;
phone:[com.example.tutorial._Person.PhoneNumber];
} namespace com.example.tutorial._Person; table PhoneNumber {
number:string (required);
type:int;
} namespace com.example.tutorial; table AddressBook {
person:[com.example.tutorial.Person];
} root_type AddressBook;

可以参考 官方的文档 来了解 .fbs 文件的详细的写法。

编译 .fbs 文件

可以通过如下命令编译 .fbs 文件:

$ flatc --java -o out addressbook.fbs

--java用于指定编译的目标编程语言。-o 参数则用于指定输出文件的路径,如过没有提供则将当前目录用作输出目录。FlatBuffers 编译器按照为不同的数据结构声明的namespace生成目录结构。对于上面的例子,会生成如下的这些文件:

$ find out
p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 11.0px Menlo}span.s1 {font-variant-ligatures: no-common-ligatures} $ find out/
out/
out//com
out//com/example
out//com/example/tutorial
out//com/example/tutorial/_Person
out//com/example/tutorial/_Person/PhoneNumber.java
out//com/example/tutorial/AddressBook.java
out//com/example/tutorial/Person.java
out//com/example/tutorial/PhoneType.java

在Android项目中使用 FlatBuffers

我们将前面由 .fbs 文件生成的Java文件拷贝到我们的项目中。我们前面提到的,FlatBuffers 的Java库比较薄,当前官方并没有发布到jcenter这样的maven仓库中,因而我们需要将这部分代码也拷贝到我们的额项目中。FlatBuffers 的Java库在其repo仓库的 java 目录下。我们有将这部分代码打包,放在公司的maven仓库中,引用的方法为,修改应用程序的 build.gradle:

repositories {
maven {
url "http://mvn.hz.netease.com/artifactory/libs-releases/"
}
maven {
url "http://mvn.hz.netease.com/artifactory/libs-snapshots/"
}
} dependencies {
compile fileTree(dir: 'libs', include: ['*.jar'])
compile project(':netlib') testCompile 'junit:junit:4.12' compile 'com.netease.hearttouch:ht-flatbuffers:0.0.1-SNAPSHOT'
}

添加访问 FlatBuffers 的类:

package com.netease.volleydemo;

import com.example.tutorial.AddressBook;
import com.example.tutorial.Person;
import com.example.tutorial._Person.PhoneNumber;
import com.google.flatbuffers.FlatBufferBuilder; import java.nio.ByteBuffer; /**
* Created by hanpfei0306 on 16-12-5.
*/ public class AddressBookFlatBuffers {
public static byte[] encodeTest(String[] names) {
FlatBufferBuilder builder = new FlatBufferBuilder(0); int[] personOffsets = new int[names.length]; for (int i = 0; i < names.length; ++ i) {
int name = builder.createString(names[i]);
int email = builder.createString("[email protected]"); int number1 = builder.createString("0157-23443276");
int type1 = 1;
int phoneNumber1 = PhoneNumber.createPhoneNumber(builder, number1, type1); int number2 = builder.createString("136183667387");
int type2 = 0;
int phoneNumber2 = PhoneNumber.createPhoneNumber(builder, number2, type2); int[] phoneNubers = new int[2];
phoneNubers[0] = phoneNumber1;
phoneNubers[1] = phoneNumber2; int phoneNumbersPos = Person.createPhoneVector(builder, phoneNubers); int person = Person.createPerson(builder, name, 13958235, email, phoneNumbersPos); personOffsets[i] = person;
}
int persons = AddressBook.createPersonVector(builder, personOffsets); AddressBook.startAddressBook(builder);
AddressBook.addPerson(builder, persons);
int eab = AddressBook.endAddressBook(builder);
builder.finish(eab);
byte[] data = builder.sizedByteArray();
return data;
} public static byte[] encodeTest(String[] names, int times) {
for (int i = 0; i < times - 1; ++ i) {
encodeTest(names);
}
return encodeTest(names);
} public static AddressBook decodeTest(byte[] data) {
AddressBook addressBook = null;
ByteBuffer byteBuffer = ByteBuffer.wrap(data);
addressBook = AddressBook.getRootAsAddressBook(byteBuffer);
return addressBook;
} public static AddressBook decodeTest(byte[] data, int times) {
AddressBook addressBook = null;
for (int i = 0; i < times; ++ i) {
addressBook = decodeTest(data);
}
return addressBook;
}
}

使用 flatbuf-gradle-plugin

我们有开发一个 FlatBuffers 的gradle插件,以方便开发,项目位置。这个插件的设计有参考Google的protobuf-gradle-plugin,功能及用法也与protobuf-gradle-plugin类似。

应用flatbuf-gradle-plugin

修改应用程序的 build.gradle 以应用flatbuf-gradle-plugin

  1. 为buildscript添加对flatbuf-gradle-plugin的依赖:

    buildscript {
    repositories {
    maven {
    url "http://mvn.hz.netease.com/artifactory/libs-releases/"
    }
    maven {
    url "http://mvn.hz.netease.com/artifactory/libs-snapshots/"
    }
    }
    dependencies {
    classpath 'com.netease.hearttouch:ht-flatbuf-gradle-plugin:0.0.1-SNAPSHOT'
    }
    }
  2. apply plugin: 'com.android.application'后面应用flatbuf的plugin:
    apply plugin: 'com.android.application'
    apply plugin: 'com.netease.flatbuf'
  3. 添加flatbuf块,对flatbuf-gradle-plugin的执行做配置:

    flatbuf {
    flatc {
    path = '/usr/local/bin/flatc'
    } generateFlatTasks {
    all().each { task ->
    task.builtins {
    remove java
    }
    task.builtins {
    java { }
    }
    }
    }
    }

    flatc块用于配置 FlatBuffers 编译器,这里我们指定用我们之前手动编译的编译器。 task.builtins的块必不可少,这个块用于指定我们要为那些编程语言生成代码,这里我们为Java生成代码。

  4. 指定 .fbs 文件的路径
     sourceSets {
    main {
    flat {
    srcDir 'src/main/flat'
    }
    }
    }

    我们将 FlatBuffers 的IDL文件放在src/main/flat目录下。

这样我们就不用再那么麻烦每次手动执行flatc了。

相关阅读:

在Android中使用FlatBuffers(上篇)

在Android中使用FlatBuffers(中篇)

在Android中使用FlatBuffers(下篇)

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本文来自网易云社区,经作者韩鹏飞授权发布。

05-18 07:12