Protocol Buffers
- protocol buffer是一个序列化数据的语言中立、平台中立、的可扩展机制
- 直白的说，就是通过中立的定义语言，生成语言相关的代码，比如生成java的pojo对象，可以方便的进行序列化和反序列化等。同时序列化后的结果，可以通过其他语言进行反序列化为其他语言能使用的结构体。
- 官网：https://developers.google.com/protocol-buffers/
- github地址：https://github.com/protocolbuffers/protobuf
- 编译器下载地址：https://github.com/protocolbuffers/protobuf/releases
Java 示例
目的
- 使用proto文件定义消息格式
- 使用protocol buffer编译器
- 使用protocol buffer API读写消息
示例说明
- 一个简单的通讯录例子，可以从文件读写联系人信息。通讯录的每个人包含一个名字，一个ID，一个邮件地址和一个联系电话。
- 对于这个需求，你有什么序列化的想法？下面列出一些解决方案：
- 使用Java序列化。问题很多（可以看Effective Java这本书）且不支持多语言
- 自己写序列化方式。需要自己解析和编码，适合简单数据
- 序列化成XML。性能低，空间利用率低
定义protpcol文件
syntax = "proto2";
package tutorial;
option java_multiple_files = true;
option java_package = "com.example.tutorial.protos";
option java_outer_classname = "AddressBookProtos";
message Person {
optional string name = 1;
optional int32 id = 2;
optional string email = 3;
enum PhoneType {
MOBILE = 0;
HOME = 1;
WORK = 2;
}
message PhoneNumber {
optional string number = 1;
optional PhoneType type = 2 [default = HOME];
}
repeated PhoneNumber phones = 4;
}
message AddressBook {
repeated Person people = 1;
}
-
从java来看，就是定义一个AddressBook对象，AddressBook包含了一个集合类型的Person。
-
Person包含了4个字段：name,id,email,phones
-
phones是PhoneNumber引用类型的，PhoneNumber包含两个字段，PhoneType为枚举
-
对应示例
package com.example.tutorial.protos;
public class AddressBookProtos{
public static class Person{
private String name;
private int id;
private String email;
private PhoneNumber phones;
public static class PhoneNumber{
private String number;
private PhoneType type=PhoneType.HOME;
public static enum PhoneType{
MOBILE,HOME,WORK;
}
}
}
public static class AddressBook{
private List<Person> people;
}
}
// 省略了getter、setter等
proto文件说明
- package用于声明包，可以作为java的包名，【必须有】多语言使用，解决定义冲突，可能不是java的反转域名规范；如果定义了java_package，使用java_package生成java包。
- java_outer_classname用于定义外部类名称，不写会使用文件名驼峰形式。my_proto.proto会使用外部名MyProto。
- java_multiple_files = true用于指示生成多个文件还是单个文件。
- 基本类型
bool,int32,float,double, andstring,enum,嵌套messge - =1，=2这些是用于定义二进制编解码的字段顺序，必须唯一，1-15只占用一个字节，最好用来定义常用的字段和可重复字段
- 每个字段有一个修饰符：required（必须）、optional（可选）、repeated（可重复）。
编译proto文件
protoc -I=$SRC_DIR --java_out=$DST_DIR $SRC_DIR/addressbook.proto
- 示例：protoc --java_out=. data.proto
protocol buffer API
- 每个类都会生成POJO类和Buidler，Builder类有getter和setter，POJO类只有getter
写数据
import com.example.tutorial.protos.AddressBook;
import com.example.tutorial.protos.Person;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.PrintStream;
class AddPerson {
// This function fills in a Person message based on user input.
static Person PromptForAddress(BufferedReader stdin,
PrintStream stdout) throws IOException {
Person.Builder person = Person.newBuilder();
stdout.print("Enter person ID: ");
person.setId(Integer.valueOf(stdin.readLine()));
stdout.print("Enter name: ");
person.setName(stdin.readLine());
stdout.print("Enter email address (blank for none): ");
String email = stdin.readLine();
if (email.length() > 0) {
person.setEmail(email);
}
while (true) {
stdout.print("Enter a phone number (or leave blank to finish): ");
String number = stdin.readLine();
if (number.length() == 0) {
break;
}
Person.PhoneNumber.Builder phoneNumber =
Person.PhoneNumber.newBuilder().setNumber(number);
stdout.print("Is this a mobile, home, or work phone? ");
String type = stdin.readLine();
if (type.equals("mobile")) {
phoneNumber.setType(Person.PhoneType.MOBILE);
} else if (type.equals("home")) {
phoneNumber.setType(Person.PhoneType.HOME);
} else if (type.equals("work")) {
phoneNumber.setType(Person.PhoneType.WORK);
} else {
stdout.println("Unknown phone type. Using default.");
}
person.addPhones(phoneNumber);
}
return person.build();
}
// Main function: Reads the entire address book from a file,
// adds one person based on user input, then writes it back out to the same
// file.
public static void main(String[] args) throws Exception {
if (args.length != 1) {
System.err.println("Usage: AddPerson ADDRESS_BOOK_FILE");
System.exit(-1);
}
AddressBook.Builder addressBook = AddressBook.newBuilder();
// Read the existing address book.
try {
addressBook.mergeFrom(new FileInputStream(args[0]));
} catch (FileNotFoundException e) {
System.out.println(args[0] + ": File not found. Creating a new file.");
}
// Add an address.
addressBook.addPerson(
PromptForAddress(new BufferedReader(new InputStreamReader(System.in)),
System.out));
// Write the new address book back to disk.
FileOutputStream output = new FileOutputStream(args[0]);
addressBook.build().writeTo(output);
output.close();
}
}
读数据
import com.example.tutorial.protos.AddressBook;
import com.example.tutorial.protos.Person;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintStream;
class ListPeople {
// Iterates though all people in the AddressBook and prints info about them.
static void Print(AddressBook addressBook) {
for (Person person: addressBook.getPeopleList()) {
System.out.println("Person ID: " + person.getId());
System.out.println(" Name: " + person.getName());
if (person.hasEmail()) {
System.out.println(" E-mail address: " + person.getEmail());
}
for (Person.PhoneNumber phoneNumber : person.getPhonesList()) {
switch (phoneNumber.getType()) {
case MOBILE:
System.out.print(" Mobile phone #: ");
break;
case HOME:
System.out.print(" Home phone #: ");
break;
case WORK:
System.out.print(" Work phone #: ");
break;
}
System.out.println(phoneNumber.getNumber());
}
}
}
// Main function: Reads the entire address book from a file and prints all
// the information inside.
public static void main(String[] args) throws Exception {
if (args.length != 1) {
System.err.println("Usage: ListPeople ADDRESS_BOOK_FILE");
System.exit(-1);
}
// Read the existing address book.
AddressBook addressBook =
AddressBook.parseFrom(new FileInputStream(args[0]));
Print(addressBook);
}
}