什么是protobuf

简单讲就是一种类似于json,xml的通用数据交换格式，但是效率更高，更省空间，目前官方支持c++,java,python,ruby。其他语言有一些第三方做的开发包，需要自己选择比较好的。

Ubuntu下快速使用

1. 下载
   google或者github

2. 编译
   2.1 编译protoc工具，这里可以直接看解压出来的protobuf-2.6.0文件夹下的README.txt文件，这里需要有c++编译器
   $ ./configure $ make $ make check $ make install
   2.2 测试安装
   $ protoc --version
   如果无法运行提示 error while loading shared libraries，我们可以直接把protoc默认安装的共享库文件路径直接加入到共享库配置文件中去（实际上很多开源软件的共享库文件默认安装的位置也在/usr/local/lib下）
   $ echo "/usr/local/lib" >> /etc/ld.so.conf $ ldconfig
   再执行一下应该就可以了
   $ protoc --version

3. java使用示例
   3.1 把java源代码编译成我们方便使用的jar包形式，这里需要用到maven，没有的话可以在这里下载apache，安装说明这页上也有
   3.2 打包，先test一下
   $ mvn test
   通过了的话直接
   $ mvn package
   在target目录下就能看到打完包的protobuf-java-2.6.0.jar文件了
   3.3 用protoc工具将.proto文件生成java类
   这里直接用刚刚下载的protobuf-2.6.0中example文件夹下的addressbook.proto文件作为示例
   $ protoc -I=$SRC_DIR --java_out=$DST_DIR $SRC_DIR/addressbook.proto
   上面的$SRC_DIR表示存放addressbook.proto文件的路径，$DST_DIR表示生成java类存放的路径
   至此将protobuf-java-2.6.0.jar和刚刚生成的AddressBookProtos.java文件引用到你自己的项目中就可以了

4. 使用
   4.1 写：AddPerson.java,为了方便直接在IDE里面使用，对官网程序做了一点修改，直接运行输入Person的相关信息就好了

    package com.example.tutorial;
   
    import java.io.BufferedReader;
    import java.io.FileInputStream;
    import java.io.FileNotFoundException;
    import java.io.FileOutputStream;
    import java.io.IOError;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.io.PrintStream;
   
    import com.example.tutorial.AddressBookProtos.AddressBook;
    import com.example.tutorial.AddressBookProtos.Person;
   
    public 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.parseInt(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);
    //      }
    
            String filePath = "myPerson";
   
            AddressBook.Builder addressBook = AddressBook.newBuilder();
   
            // Read the existing address book.
            try {
                addressBook.mergeFrom(new FileInputStream(filePath));
            } catch (FileNotFoundException e) {
                System.out.println(filePath
                        + ": 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(filePath);
            addressBook.build().writeTo(output);
            output.close();
        }
   
    }
   

4.2 读：可以读取刚刚写在文件里的Person

    package com.example.tutorial;

    import java.io.FileInputStream;

    import com.example.tutorial.AddressBookProtos.AddressBook;
    import com.example.tutorial.AddressBookProtos.Person;

    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.
        public static void main(String[] args) throws Exception {
            String filePath = "myPerson";

            // Read the existing address book.
            AddressBook addressBook = AddressBook.parseFrom(new FileInputStream(filePath));

            Print(addressBook);
        }

    }