Thu Dec 6, 2012
Creating a simple message in Google Protobuf - contact.proto
We’ll start off by creating the message or data format for our contact app. Create a new protocol buffer descriptor file using the new wizard, call it contact.proto and save it inside the contactsmanager package.
The contents of the proto file is below. The message itself is very simple. That’s because, our tutorial is very simple.
package contactsmanager.proto; //The package where the compiled version of this object is saved
// The name of the message. It is important not to give the same name as the proto file name// i.e. the message name Contact would not compile. This issue can be avoided by using the java_outer_classname option
message PContact { //the optional keyword indicates that the field may or may not be set. When parsing this message, if optional value is not set, then default value is used
optional string firstName = 1;
optional string middleName = 2;
optional string lastName = 3;
optional string mobile = 4;
optional string homepage = 5;
}
Once you save the .proto file, the protobuf compiler compiles it automatically and creates the corresponding java file for reading/writing to the message in you project folder. The folder it creates it: src-gen *You need to link up this folder as source folder so that when we use the PContact.java file, eclipse can include it automatically in the imports. Right click on the contacts-manager* project that we are working on and link up the src-gen folder in java build path. This is illustrated below.
Wiring the code for saving/reading data to protobuf format
First thing we have to do is incude the google-protobuf-2.4.1 plugin in our contacts-manager rcp dependencies list.
Next, open up ContactFormPage.java in Window Builder moder. Double click on the save button. The builder automatically creates a click handler and switches to code mode. In the code create a new method called performSave().** Also, call the method *performSave() *inside the button event handler.
private void performSave() {
String firstName = txtFirstName.getText().trim();
String middleName = txtMiddleName.getText().trim();
String lastName = txtLastName.getText().trim();
String mobile = txtMobile.getText().trim();
String homepage = txtHomePage.getText().trim();
//the compiled java class has in-built builder for creating objects of the PContact class
PContact contact = PContact.newBuilder().setFirstName(firstName)
.setMiddleName(middleName).setLastName(lastName)
.setMobile(mobile).setHomepage(homepage).build();
//save the contents of contact (byte array) to file using eclipse resources api
IFile file = ((FileEditorInput) getEditorInput()).getFile();
ByteArrayInputStream baio = new ByteArrayInputStream(contact.toByteArray());
try {
file.setContents(baio, false, false, null);
} catch (CoreException e) {
e.printStackTrace();
}
}
Now, we’ll create another method that loads the data from the file. Create loadContact() *and call the method inside createFormContent()* method.
@Override
protected void createFormContent(IManagedForm managedForm) {
FormToolkit toolkit = managedForm.getToolkit();
ScrolledForm form = managedForm.getForm();
form.setText("Simple Contact Manager");
Composite body = form.getBody();
toolkit.decorateFormHeading(form.getForm());
toolkit.paintBordersFor(body);
.
.
.
loadContact();
}
private void loadContact() {
IFile file = ((FileEditorInput) getEditorInput()).getFile();
try {
PContact contact = PContact.parseFrom(file.getContents());
txtFirstName.setText(contact.getFirstName());
txtMiddleName.setText(contact.getMiddleName());
txtLastName.setText(contact.getLastName());
txtMobile.setText(contact.getMobile());
txtHomePage.setText(contact.getHomepage());
} catch (IOException e) {
e.printStackTrace();
} catch (CoreException e) {
e.printStackTrace();
}
}