Protocol Buffer入门——搭建环境(JAVA版)

Protocol Buffers简介：

Protocol Buffers 是一种轻便高效的结构化数据存储格式，可以用于结构化数据串行化，很适合做数据存储或 RPC 数据交换格式。它可用于通讯协议、数据存储等领域的语言无关、平台无关、可扩展的序列化结构数据格式。目前提供了 C++、Java、Python 三种语言的 API。

Protocol Buffers环境搭建（JAVA）：

准备：下载protobuf-java-2.5.0.zip(里面包含protobuf-java-2.5.0.jar和protoc.exe编辑器)

步骤：

1.新建java工程test_protobufers

2.导入protobuf-java-2.5.0.jar，并将protoc.exe编辑器放到test_protobufers项目工程根目录下。

3.test_protobufers项目工程根目录下创建proto文件夹，用于存放.proto的文件。

4.编写Message放到proto文件夹下，引用官网的例子，创建addressbook.proto代码如下：

package tutorial;option java_package = "com.example.tutorial";//编译后生成的文件存放的位置option java_outer_classname = "AddressBookProtos";//编译后生成的文件的名字message Person {  required string name = 1;  required int32 id = 2;        // Unique ID number for this person.  optional string email = 3;  enum PhoneType {    MOBILE = 0;    HOME = 1;    WORK = 2;  }  message PhoneNumber {    required string number = 1;    optional PhoneType type = 2 [default = HOME];  }  repeated PhoneNumber phone = 4;}// Our address book file is just one of these.message AddressBook {  repeated Person person = 1;}

5.编译addressbook.proto成指定的java类，命令行下进入编译器所在目录，执行如下命令：

     protoc -I=proto/ --java_out=src proto/addressbook.proto

其中，src为生成的java类的目标位置，这里我们选择项目的默认包，proto/addressbook.proto表示我们的proto文件，运行后即生成java类，生成的java类被放在了package com.example.tutorial中。与上面代码中option java_package 指定的参数有关系。

6.现在有了生成的AddressBookProtos.java类，我们可以向文件里写入消息了，首先编写AddPerson.java,代码如下：

import com.example.tutorial.AddressBookProtos.AddressBook;import com.example.tutorial.AddressBookProtos.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{    // 这个函数将会根据用户的输入填充一个用户的信息  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.addPhone(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();    } }

7.首先配置参数，也就是消息被序列化后存储的文件名，这里，我们就把参数设置成AddressBook。运行时如果文件不存在，将会创建文件并写入；如果存在，就写入。运行程序，按照提示输入消息。然后查看我们的项目路径下，将会产生AddressBook文件。（AddressBook可以换成自己想要的名字。）
8.上一步是将消息序列化到文件中，这一步将文件中的消息反序列化，类似地，我们创建一个类：ListPeople.java 代码如下：

import com.example.tutorial.AddressBookProtos.AddressBook;import com.example.tutorial.AddressBookProtos.Person;import java.io.FileInputStream;public class ListPeople {// Iterates though all people in the AddressBook and prints info about them.static void Print(AddressBook addressBook) {for (Person person : addressBook.getPersonList()) {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.getPhoneList()) {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./** * @param args * @throws Exception */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);}}

输入参数AddressBook（第7步中设置的参数）并运行程序，将会看到我们输入的消息体被遍历并打印出来了！