Protocol Buffers(以下簡(jiǎn)稱PB) 是google 的一種數(shù)據(jù)交換的格式。PB獨(dú)立于語(yǔ)言恒序，獨(dú)立于平臺(tái)三圆，相比于json，xml等基于字符的數(shù)據(jù)封裝格式污呼，PB是一種效率和兼容性都很優(yōu)秀的二進(jìn)制數(shù)據(jù)傳輸格式裕坊，可以用于諸如網(wǎng)絡(luò)傳輸、配置文件燕酷、數(shù)據(jù)存儲(chǔ)等諸多領(lǐng)域籍凝。在數(shù)據(jù)包體積方面，PB的優(yōu)勢(shì)尤為明顯苗缩，使用PB封裝的數(shù)量包體積要遠(yuǎn)小于json或xml（根據(jù)一些網(wǎng)上公開(kāi)的測(cè)試結(jié)果饵蒂，封裝同樣的數(shù)據(jù)，PB的數(shù)據(jù)包大小是json的三分之一左右）酱讶，所以PB非常適合網(wǎng)絡(luò)數(shù)據(jù)的傳輸退盯，特別對(duì)于數(shù)據(jù)量和網(wǎng)速都受限的移動(dòng)網(wǎng)絡(luò)，使用PB對(duì)提升用戶的體驗(yàn)?zāi)芷鸬椒浅７e極的作用。 但是PB的缺點(diǎn)也是明顯的渊迁，一個(gè)簡(jiǎn)單的message經(jīng)過(guò)compile后會(huì)生成一個(gè)復(fù)雜的源碼文件慰照，即使只定義了一個(gè)field，源碼文件里也會(huì)有數(shù)十個(gè)方法琉朽，這些方法都是在PB的runtime庫(kù)需要用到的毒租，在服務(wù)端使用倒沒(méi)什么，但是用到Android端就麻煩了箱叁，隨著網(wǎng)絡(luò)協(xié)議的豐富墅垮，與之對(duì)應(yīng)的PB數(shù)據(jù)結(jié)構(gòu)包的方法數(shù)會(huì)急劇膨脹，大大加快應(yīng)用觸碰到64K方法數(shù)超界這塊天花板的時(shí)間耕漱。
Wire-Lite作為Android平臺(tái)的PB庫(kù)噩斟，在開(kāi)源庫(kù)[Wire]的基礎(chǔ)上再次做了大幅度的精簡(jiǎn)，相比于另一個(gè)著名的PB庫(kù)protobuf孤个，可將方法數(shù)精簡(jiǎn)70%以上剃允，相比于其前身Wire，也可精簡(jiǎn)接近50%齐鲤，非常適合在移動(dòng)端使用斥废。
Wire-Lite功能及演示
通過(guò)一個(gè)例子對(duì)比不同PB庫(kù)的區(qū)別：
例子proto:
package com.example;
option java_package = "com.example";
option java_outer_classname = "PersonProtos";
message Person {
// The customer's full name.
required string name = 1;
// The customer's ID number.
required int32 id = 2;
// Email address for the customer.
optional string email = 3;
}
這個(gè)proto定義了名為Person的message，很簡(jiǎn)單给郊，只有name, id, email共3個(gè)field牡肉，讓我們看看四個(gè)庫(kù)編譯后的結(jié)果：
使用google的protobuf庫(kù)編譯后為：
package com.example;
public final class PersonProtos {
private PersonProtos() {}
public static void registerAllExtensions(
com.google.protobuf.ExtensionRegistry registry) {
}
public interface PersonOrBuilder
extends com.google.protobuf.MessageOrBuilder {
// required string name = 1;
/**
* <code>required string name = 1;</code>
*
* <pre>
* The customer's full name.
* </pre>
*/
boolean hasName();
/**
* <code>required string name = 1;</code>
*
* <pre>
* The customer's full name.
* </pre>
*/
java.lang.String getName();
/**
* <code>required string name = 1;</code>
*
* <pre>
* The customer's full name.
* </pre>
*/
com.google.protobuf.ByteString
getNameBytes();
// required int32 id = 2;
/**
* <code>required int32 id = 2;</code>
*
* <pre>
* The customer's ID number.
* </pre>
*/
boolean hasId();
/**
* <code>required int32 id = 2;</code>
*
* <pre>
* The customer's ID number.
* </pre>
*/
int getId();
.........
因?yàn)樯傻奈募?02行，太多了淆九，所以只粘一小部分示意一下统锤，對(duì)于只有3個(gè)field的message卻生成了如此多的代碼，過(guò)于冗余了炭庙。
使用protostuff編譯后為：
// Generated by http://code.google.com/p/protostuff/ ... DO NOT EDIT!
// Generated from example.proto
package com.example;
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
import com.dyuproject.protostuff.GraphIOUtil;
import com.dyuproject.protostuff.Input;
import com.dyuproject.protostuff.Message;
import com.dyuproject.protostuff.Output;
import com.dyuproject.protostuff.Schema;
import com.dyuproject.protostuff.UninitializedMessageException;
public final class Person implements Externalizable, Message<Person>, Schema<Person>
{
public static Schema<Person> getSchema()
{
return DEFAULT_INSTANCE;
}
public static Person getDefaultInstance()
{
return DEFAULT_INSTANCE;
}
static final Person DEFAULT_INSTANCE = new Person();
private String name;
private Integer id;
private String email;
public Person()
{
}
public Person(
String name,
Integer id
)
{
this.name = name;
this.id = id;
}
// getters and setters
// name
public String getName()
{
return name;
}
public void setName(String name)
{
this.name = name;
}
// id
public Integer getId()
{
return id;
}
public void setId(Integer id)
{
this.id = id;
}
// email
public String getEmail()
{
return email;
}
public void setEmail(String email)
{
this.email = email;
}
// java serialization
public void readExternal(ObjectInput in) throws IOException
{
GraphIOUtil.mergeDelimitedFrom(in, this, this);
}
public void writeExternal(ObjectOutput out) throws IOException
{
GraphIOUtil.writeDelimitedTo(out, this, this);
}
// message method
public Schema<Person> cachedSchema()
{
return DEFAULT_INSTANCE;
}
// schema methods
public Person newMessage()
{
return new Person();
}
public Class<Person> typeClass()
{
return Person.class;
}
public String messageName()
{
return Person.class.getSimpleName();
}
public String messageFullName()
{
return Person.class.getName();
}
public boolean isInitialized(Person message)
{
return
message.name != null
&& message.id != null;
}
public void mergeFrom(Input input, Person message) throws IOException
{
for(int number = input.readFieldNumber(this);; number = input.readFieldNumber(this))
{
switch(number)
{
case 0:
return;
case 1:
message.name = input.readString();
break;
case 2:
message.id = input.readInt32();
break;
case 3:
message.email = input.readString();
break;
default:
input.handleUnknownField(number, this);
}
}
}
public void writeTo(Output output, Person message) throws IOException
{
if(message.name == null)
throw new UninitializedMessageException(message);
output.writeString(1, message.name, false);
if(message.id == null)
throw new UninitializedMessageException(message);
output.writeInt32(2, message.id, false);
if(message.email != null)
output.writeString(3, message.email, false);
}
public String getFieldName(int number)
{
return Integer.toString(number);
}
public int getFieldNumber(String name)
{
return Integer.parseInt(name);
}
}
protostuff編譯后只有184行饲窿，但方法數(shù)還是多，有22個(gè)焕蹄，除了get, set方法外逾雄，還有很多輔助方法，性價(jià)比不高腻脏。
使用wire編譯后為：
// Code generated by Wire protocol buffer compiler, do not edit.
// Source file: /Users/aoxiao/Develop/protostuff/example.proto
package com.example;
import com.squareup.wire.Message;
import com.squareup.wire.ProtoField;
import static com.squareup.wire.Message.Datatype.INT32;
import static com.squareup.wire.Message.Datatype.STRING;
import static com.squareup.wire.Message.Label.REQUIRED;
public final class Person extends Message {
public static final String DEFAULT_NAME = "";
public static final Integer DEFAULT_ID = 0;
public static final String DEFAULT_EMAIL = "";
/**
* The customer's full name.
*/
@ProtoField(tag = 1, type = STRING, label = REQUIRED)
public final String name;
/**
* The customer's ID number.
*/
@ProtoField(tag = 2, type = INT32, label = REQUIRED)
public final Integer id;
/**
* Email address for the customer.
*/
@ProtoField(tag = 3, type = STRING)
public final String email;
public Person(String name, Integer id, String email) {
this.name = name;
this.id = id;
this.email = email;
}
private Person(Builder builder) {
this(builder.name, builder.id, builder.email);
setBuilder(builder);
}
@Override
public boolean equals(Object other) {
if (other == this) return true;
if (!(other instanceof Person)) return false;
Person o = (Person) other;
return equals(name, o.name)
&& equals(id, o.id)
&& equals(email, o.email);
}
@Override
public int hashCode() {
int result = hashCode;
if (result == 0) {
result = name != null ? name.hashCode() : 0;
result = result * 37 + (id != null ? id.hashCode() : 0);
result = result * 37 + (email != null ? email.hashCode() : 0);
hashCode = result;
}
return result;
}
public static final class Builder extends Message.Builder<Person> {
public String name;
public Integer id;
public String email;
public Builder() {
}
public Builder(Person message) {
super(message);
if (message == null) return;
this.name = message.name;
this.id = message.id;
this.email = message.email;
}
/**
* The customer's full name.
*/
public Builder name(String name) {
this.name = name;
return this;
}
/**
* The customer's ID number.
*/
public Builder id(Integer id) {
this.id = id;
return this;
}
/**
* Email address for the customer.
*/
public Builder email(String email) {
this.email = email;
return this;
}
@Override
public Person build() {
checkRequiredFields();
return new Person(this);
}
}
}
wire編譯后為116行鸦泳，方法數(shù)減少到10個(gè)，減少的原因一方面是輔助方法數(shù)少了永品，另一方面是其使用了annotation做鹰，精簡(jiǎn)了get, set方法。 不過(guò)為了創(chuàng)建一個(gè)Person實(shí)例鼎姐，wire又為每個(gè)message提供了一個(gè)Builder钾麸，里面為各field設(shè)置值的方法相當(dāng)于把set方法又加了回來(lái)掉弛，當(dāng)然Builder在build時(shí)會(huì)做很多有效性檢查的工作，但是仍有精簡(jiǎn)的余地喂走。
使用wire-lite編譯后為：
// Code generated by Wire-Lite protocol buffer compiler, do not edit.
// Source file: /Users/aoxiao/Develop/protostuff/example.proto
package com.example;
import com.squareup.wire.Message;
import com.squareup.wire.ProtoField;
import static com.squareup.wire.Message.Datatype.INT32;
import static com.squareup.wire.Message.Datatype.STRING;
import static com.squareup.wire.Message.Label.REQUIRED;
public final class Person extends Message {
public static final int TAG_NAME = 1;
public static final int TAG_ID = 2;
public static final int TAG_EMAIL = 3;
public static final String DEFAULT_NAME = "";
public static final Integer DEFAULT_ID = 0;
public static final String DEFAULT_EMAIL = "";
/**
* The customer's full name.
*/
@ProtoField(tag = 1, type = STRING, label = REQUIRED)
public String name;
/**
* The customer's ID number.
*/
@ProtoField(tag = 2, type = INT32, label = REQUIRED)
public Integer id;
/**
* Email address for the customer.
*/
@ProtoField(tag = 3, type = STRING)
public String email;
public Person(Person message) {
super(message);
if (message == null) return;
this.name = message.name;
this.id = message.id;
this.email = message.email;
}
public Person() {
}
public Person fillTagValue(int tag, Object value) {
switch(tag) {
case TAG_NAME:
this.name = (String)value;
break;
case TAG_ID:
this.id = (Integer)value;
break;
case TAG_EMAIL:
this.email = (String)value;
break;
default: break;
};
return this;
}
@Override
public boolean equals(Object other) {
if (other == this) return true;
if (!(other instanceof Person)) return false;
Person o = (Person) other;
return equals(name, o.name)
&& equals(id, o.id)
&& equals(email, o.email);
}
@Override
public int hashCode() {
int result = hashCode;
if (result == 0) {
result = name != null ? name.hashCode() : 0;
result = result * 37 + (id != null ? id.hashCode() : 0);
result = result * 37 + (email != null ? email.hashCode() : 0);
hashCode = result;
}
return result;
}
}
wire-lite編譯后的類行數(shù)減少到88行， 方法數(shù)減少到5個(gè)谋作，與wire生成的代碼對(duì)比可見(jiàn)其精簡(jiǎn)了Builder類芋肠，改為直接創(chuàng)建message實(shí)例并可對(duì)field賦值 （wire中的field是final的，生成后不可更改）遵蚜， 原Builder中對(duì)數(shù)據(jù)有效性的檢查則放到序列化或反序列化之前做帖池。通過(guò)這些改造，使得生成代碼的方法數(shù)基本等于甚至小于field數(shù)吭净，這在編譯有很多屬性的proto文件時(shí)效果尤為明顯睡汹。
wire-lite的另一個(gè)較大變動(dòng)是增加了fillTagValue方法，這樣可以通過(guò)key/value的形式鏈?zhǔn)皆O(shè)置field的值寂殉，這個(gè)方法的目的是取代Builder的鏈?zhǔn)秸{(diào)用囚巴，達(dá)到同樣可以快速創(chuàng)建實(shí)例的目的，同時(shí)又把方法數(shù)收縮到了一個(gè)友扰，這在復(fù)雜proto結(jié)構(gòu)的生成中是比較常見(jiàn)的彤叉，例如下面這個(gè)proto設(shè)置了多個(gè)自定義的option:
extend google.protobuf.FieldOptions {
optional int32 my_field_option_one = 60001;
optional float my_field_option_two = 60002;
optional FooBar.FooBarBazEnum my_field_option_three = 60003;
optional FooBar my_field_option_four = 60004;
}
message FooBar {
extensions 100 to 200;
optional int32 foo = 1 [my_field_option_one = 17];
optional string bar = 2 [my_field_option_two = 33.5];
optional Nested baz = 3 [my_field_option_three = BAR];
optional uint64 qux = 4 [my_field_option_one = 18, my_field_option_two = 34.5];
repeated float fred = 5 [my_field_option_four = {
foo: 11, bar: "22", baz: { value: BAR }, fred : [444.0, 555.0],
nested: { foo: 33, fred: [100.0, 200.0] }
}, my_field_option_two = 99.9];
optional double daisy = 6 [my_field_option_four.baz.value = FOO];
......
用wire生成的代碼為：
public static final MessageOptions MESSAGE_OPTIONS = new MessageOptions.Builder()
.setExtension(Ext_custom_options.my_message_option_one, new FooBar.Builder()
.foo(1234)
.bar("5678")
.baz(new FooBar.Nested.Builder()
.value(FooBar.FooBarBazEnum.BAZ)
.build())
.qux(-1L)
.fred(java.util.Arrays.asList(
123.0F,
321.0F))
.daisy(456.0D)
.build())
......
用wire-lite生成的代碼為：
public static final MessageOptions MESSAGE_OPTIONS = new MessageOptions.Builder()
.setExtension(Ext_custom_options.my_message_option_one, new FooBar()
.fillTagValue(FooBar.TAG_FOO, 1234)
.fillTagValue(FooBar.TAG_BAR, "5678")
.fillTagValue(FooBar.TAG_BAZ, new FooBar.Nested()
.fillTagValue(FooBar.Nested.TAG_VALUE, FooBar.FooBarBazEnum.BAZ)
)
.fillTagValue(FooBar.TAG_QUX, -1L)
.fillTagValue(FooBar.TAG_FRED, java.util.Arrays.asList(
123.0F,
321.0F))
.fillTagValue(FooBar.TAG_DAISY, 456.0D)
)
......
從兩段代碼的對(duì)比中可見(jiàn)，通過(guò)fillTagValue來(lái)進(jìn)行鏈?zhǔn)劫x值比wire中使用Builder稍多了一點(diǎn)代碼村怪，但是方法數(shù)大為減少秽浇，還是可以接受的，而且這種調(diào)用多在自動(dòng)生成的代碼中出現(xiàn)甚负，在日常編碼中柬焕，一般采用直接賦值的方式。
如何使用wire-lite
wire-lite的使用方法與wire基本一致梭域，可以參考wire項(xiàng)目的主頁(yè) https://github.com/square/wire 這里主要說(shuō)一下不同的地方：
- 編譯 編譯proto文件有兩種選擇斑举，一是下載jar包對(duì)proto文件進(jìn)行編譯，jar包地址為： http://mvnrepo.alibaba-inc.com/nexus/service/local/artifact/maven/redirect?r=snapshots&g=com.squareup.wire&a=wire-lite-compiler&v=1.5.3-SNAPSHOT&e=jar&c=jar-with-dependencies
二是使用maven插件編譯
<plugin>
<groupId>com.squareup.wire</groupId>
<artifactId>wire-lite-maven-plugin</artifactId>
<executions>
<execution>
<phase>generate-sources</phase>
<goals>
<goal>generate-sources</goal>
</goals>
<configuration>
<protoFiles>
<param>squareup/wire/exemplar.proto</param>
</protoFiles>
<serviceWriter>com.squareup.wire.SimpleServiceWriter</serviceWriter>
</configuration>
</execution>
</executions>
</plugin>
使用方法見(jiàn)wire項(xiàng)目的說(shuō)明
- 引用runtime庫(kù) 在maven配置中依賴wire-lite的runtime庫(kù)即可
<dependency>
<groupId>com.squareup.wire</groupId>
<artifactId>wire-lite-runtime</artifactId>
<version>1.5.3-SNAPSHOT</version>
</dependency>
- 創(chuàng)建對(duì)象 wire-lite創(chuàng)建對(duì)象與賦值的方式更為簡(jiǎn)單病涨，以上文的Person為例：
Person person = new Person(); //創(chuàng)建對(duì)象
person.id = 111; //直接對(duì)field賦值
person.email = "test@test.com";
//當(dāng)然也可以通過(guò)fillTagValue賦值懂昂，每個(gè)key都是全大寫，以field name加上TAG_前綴
person.fillTagValue(Person.TAG_NAME, "Mike");
Person newPerson = new Person(person); //創(chuàng)建一個(gè)對(duì)象没宾，并從一個(gè)已有對(duì)象處復(fù)制所有值
- 序列化與反序列化
byte[] personData = person.toByteArray(); //直接轉(zhuǎn)到byte數(shù)組
//或者先創(chuàng)建數(shù)據(jù)再寫入
byte[] newPersonData = new byte[person.getSerializedSize()];
person.witeTo(newPersonData);
//反序列化
Wire wire = new Wire();
Person newPersonInstance = wire.parseFrom(personData, Person.class);
- 有效性檢查 在wire中凌彬，有效性檢查發(fā)生在build對(duì)象時(shí)期，主要包括對(duì)require field的檢查以及數(shù)組中null元素的檢查循衰，而在wire-lite中铲敛，有效性檢查發(fā)生在序列化與反序列化時(shí)期，也就是說(shuō)第3點(diǎn)中的代碼都會(huì)進(jìn)行檢查会钝，如果數(shù)據(jù)不合法（必填項(xiàng)為null或者數(shù)組中有null值）伐蒋，則會(huì)拋出 IllegalStateException 或 NullPointerException 工三，換句話說(shuō)，就是wire-lite認(rèn)為PB對(duì)象在序列化或反序列化時(shí)都應(yīng)該是合法的先鱼，而其出錯(cuò)拋異常的方式與wire一致俭正。
目前wire-lite項(xiàng)目的進(jìn)展：
wire-lite項(xiàng)目有compiler, runtime, maven-plugin三個(gè)工程，均通過(guò)了所有的單元測(cè)試焙畔，也就是說(shuō)處于立即可用的狀態(tài)掸读。在maven倉(cāng)庫(kù)中也有對(duì)應(yīng)的SNAPSHOT包，版本為1.5.3, 這是由于wire-lite是基于wire 1.5.3版本改動(dòng)而來(lái)宏多，所以版本號(hào)上保持了一致儿惫， 如果有同學(xué)還有更好的精簡(jiǎn)方案，非常歡迎加入進(jìn)來(lái)伸但，我們一起把這個(gè)庫(kù)做的更好更穩(wěn)定.
關(guān)于Android L Preview版本的問(wèn)題：
目前wire-lite在Android L Preview版本上會(huì)出現(xiàn)崩潰的情況肾请，這其實(shí)是google的問(wèn)題，google在preview版中引入了okio等開(kāi)源庫(kù)更胖，但沒(méi)有repackage铛铁，這會(huì)與wire-lite中引用的okio庫(kù)沖突，導(dǎo)致 IllegalAccessErrorException却妨。google已經(jīng)明確表示在Android L正式版中會(huì)解決這個(gè)問(wèn)題避归，將okio等包加上com.android的前綴，所以wire-lite和wire一樣管呵，不會(huì)針對(duì)preview版本做適配性修復(fù)梳毙，如果有同學(xué)一定要在preview版本中使用的話，可以自己用jarjar等工具做repackage捐下。
