Protobuff in android:
I am writing this blog on .proto file communication because as I try to search for the same I did not found much solution on the same. So I have try to make simplify with example so that everyone understand easily. I hope this blog would be helpful for developers
There are few choices in android that can be used for sharing data or transfer data over the network like rest and soap few way of communication json parsing, Xml parsing, Soap parsing (xml) etc.
Here I want to explain one more way to communicate is protobuf API . This provide faster performance rather than XML and JSON.
In android we use this over HTTP Url connection or Http client. Data travels in the binary format.
There is a basic reason for faster performance i.e. XML is notoriously space intensive, and encoding/decoding it can impose a huge performance penalty on applications.
Requirement for protobuff communication is
1. Define message formats in a .proto file.
2. Use the protocol buffer compiler.
3. Use the Java protocol buffer API to write and read messages.
4. And require google protobuf.jar library
In this method you have to configure a proto file that contains message format which we use for parsing data.
Here I am showing an example addressbook.proto file which you find on google site also.
1) Define Protocol Format
To create your address book application, you'll need to start with a .proto file. The definitions in a .proto file are simple: you add a message for each data structure you want to serialize, then specify a name and a type for each field in the message.
package tutorial;
option java_package = "com.example.tutorial";
option java_outer_classname = "AddressBookProtos";
message Person {
required string name = 1;
required int32 id = 2;
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;
}
message AddressBook {
repeated Person person = 1;
}
2) Compilation of .proto
Here is steps for compile .proto file
Now run the compiler, specifying the source directory (where your application's source code lives – the current directory is used if you don't provide a value), the destination directory (where you want the generated code to go; often the same as $SRC_DIR), and the path to your .proto. In this case, you...:
protoc -I=$SRC_DIR --java_out=$DST_DIR $SRC_DIR/addressbook.proto
Because you want Java classes, you use the --java_out option – similar options are provided for other supported languages.
If you look in AddressBookProtos.java (Generated File), you can see that it defines a class called AddressBookProtos, nested within which is a class for each message you specified in addressbook.proto. Each class has its ownBuilder class that you use to create instances of that class. You can find out more about builders in the
Builders vs. Messages section below.
Both messages and builders have auto-generated accessor methods for each field of the message; messages have only getters while builders have both getters and setters. Here are some of the accessors for the Personclass (implementations omitted for brevity)
Here is few sample code
/ required string name = 1;
public boolean hasName();
public java.lang.String getName();
public Builder setName(String value);
public Builder clearName();
// required int32 id = 2;
public boolean hasId();
public int getId();
public Builder setId(int value);
public Builder clearId();
// optional string email = 3;
public boolean hasEmail();
public String getEmail();
public Builder setEmail(String value);
public Builder clearEmail();
// repeated .tutorial.Person.PhoneNumber phone = 4;
public List<PhoneNumber> getPhoneList();
public int getPhoneCount();
public PhoneNumber getPhone(int index);
public Builder setPhone(int index, PhoneNumber value);
public Builder addPhone(PhoneNumber value);
public Builder addAllPhone(Iterable<PhoneNumber> value);
public Builder clearPhone();
3) Writing a message
Here is a program which reads an AddressBook from a file, adds one new Person to it based on user input, and writes the new AddressBook back out to the file again. The parts which directly call or reference code generated by the protocol compiler are highlighted
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 {
// 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.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();
}
}
4) Reading a message
In this communication data send and receive as a Raw data in byte array format therefore in serialize and desterilize you have to convert using following methods
byte[] toByteArray();: serializes the message and returns a byte array containing its raw bytes.
static Person parseFrom(byte[] data);: parses a message from the given byte array.
void writeTo(OutputStream output);: serializes the message and writes it to an OutputStream.
static Person parseFrom(InputStream input);: reads and parses a message from an InputStream
Example to read message:
import com.example.tutorial.AddressBookProtos.AddressBook;
import com.example.tutorial.AddressBookProtos.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.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 {
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);
}
}
5) Sample code to send data over the network
Here is an example for sending byte array which we marshaled with protobuff message format
public static Object callServerWithPayload(String methodName, byte[] data, String... params)
{
DefaultHttpClient client = new DefaultHttpClient();
StringBuilder sb = new StringBuilder();
sb.append(SERVER_ADDRESS + SERVLET_PATH);
sb.append(“/”).append(methodName);
for (String param : params)
{
sb.append(“/”).append(URLEncoder.encode(param));
}
HttpPost method = new HttpPost(sb.toString());
method.setEntity(new ByteArrayEntity(data));
try
{
HttpResponse response = client.execute(method);
return response.getEntity().getContent();
}
catch (Exception e)
{
App.logException(e);
}
