Download Android-Chapter14-JSON Encoding

CIS 470
Quick Notes: Android & JSON encoding
GOALS: Encode/Decode locally. Access a server to read a file holding JSON encoded data, decode, show results.
package csu.matos;
import
import
import
import
import
import
import
android.app.Activity;
android.os.Bundle;
android.os.Handler;
android.os.Message;
android.view.View;
android.widget.ProgressBar;
android.widget.TextView;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import
import
import
import
java.lang.reflect.Type;
java.net.URL;
java.util.ArrayList;
java.util.Scanner;
public class MainActivity extends Activity {
ProgressBar progressBar;
TextView txtMsg;
Gson gson;
Handler handler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
txtMsg.append("\n" + (String) msg.obj);
progressBar.setVisibility(View.INVISIBLE);
}
};
Thread slowWorkerThread = new Thread() {
@Override
public void run() {
super.run();
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
//a little delay here (dramatic effect)...
}
String text;
//PART2: JSON Encoding
Person person0 = new Person("Daenerys", 20);
// convert Person (Java object) to JSON format
// display it as a JSON formatted string
Gson gson = new Gson();
String json = gson.toJson(person0);
text = "\n(LOCAL)Json serialized object:\n" + json;
handler.sendMessage(handler.obtainMessage(1, text));
// create a few more Person objects
Person person1 = new Person("Arya", 12);
Person person2 = new Person("Cersei", 35);
// place all Person objects in an ArrayList
ArrayList<Person> lstPerson = new ArrayList<>();
lstPerson.add(person0);
lstPerson.add(person1);
lstPerson.add(person2);
// convert Java ArrayList to JSON string
String jsonList = gson.toJson(lstPerson);
text = "\n(LOCAL)Json serialized list:\n" + jsonList;
handler.sendMessage(handler.obtainMessage(1, text));
// use Java reflection to find the list's type
Type arrayPersonType = new TypeToken<ArrayList<Person>>(){}.getType();
// deserialize JSON string representing the list of objects
ArrayList<Person> lst2 = gson.fromJson(jsonList, arrayPersonType);
// explore the Java ArrayList
for(int i=0; i<lst2.size(); i++){
Person p = lst2.get(i);
text = "\n" + i + "-(LOCAL) Person From Deserialized List:\n" + p.toString()
+ "\n
name:" + p.getName()
+ "\n
age: " + p.getAge();
handler.sendMessage(handler.obtainMessage(1, text));
}
try {
//URL url = new URL("http://informatos.org/westeros_ladies.txt");
//URL url = new URL("http://192.168.1.70/westeros/westeros_ladies.txt");
//URL url = new URL("http://informatos.org/westeros_ladies.txt");
//URL url = new URL("http://192.168.1.70/westeros/westeros_ladies.txt");
//--------------------------------------------------------------------------------URL url = new URL("http://grail.csuohio.edu/~matos/gameofthrones/westeros_ladies.txt");
//URL url = new URL("http://grail.cba.csuohio.edu/~matos/gameofthrones/getPersonNoSql.php");
URL url = new
URL("http://grail.cba.csuohio.edu/~matos/gameofthrones/getPersonNoSql.php?castle=winterfell");
//URL url = new
URL("http://grail.cba.csuohio.edu/~matos/gameofthrones/getPersonNoSql.php?castle=dragonstone");
//URL url = new
URL("http://grail.cba.csuohio.edu/~matos/gameofthrones/getPersonNoSql.php?castle=kings_landing");
// -------------------------------------------------------------------------------// next statement reads the ENTIRE file (delimiter \A matches All input)
// String text = new Scanner( url.openStream() ).useDelimiter("\\A").next();
// ------------------------------------------------------------------------// scanning a remote file one line at the time
text ="";
Scanner scanner = new Scanner(url.openStream());
while (scanner.hasNext()) {
text += scanner.nextLine() + "\n";
}
handler.sendMessage(handler.obtainMessage(1, "\nFROM REMOTE SERVER\n" + url.toString()));
handler.sendMessage(handler.obtainMessage(1, "\nREMOTE JSON STR\n" + text));
// use Java reflection to find the list's type
Type arrayPersonType3 = new TypeToken<ArrayList<Person>>(){}.getType();
// deserialize JSON string representing the list of objects
ArrayList<Person> lst3 = gson.fromJson(jsonList, arrayPersonType3);
// explore the Java ArrayList
for(int i=0; i<lst3.size(); i++){
Person p = lst3.get(i);
text = "\n" + i + "-(REMOTE)Person From Deserialized List:\n" + p.toString()
+ "\n
name:" + p.getName()
+ "\n
age: " + p.getAge();
handler.sendMessage(handler.obtainMessage(1, text));
}
} catch (java.io.IOException e) {
handler.sendMessage(handler.obtainMessage(1, "ERROR: " + e.getMessage()));
}
}//run
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
txtMsg = (TextView) findViewById(R.id.txtMsg);
progressBar = (ProgressBar)findViewById(R.id.progressBar);
slowWorkerThread.start();
}//onCreate
}
Person class
package csu.matos;
public class Person {
private String name;
private Integer age;
public Person (String name, Integer age) {
this.name = name; this.age = age;
}
public Person() {
this.name = "n.a.";
this.age=0;
};
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public String toString() {
return "PERSON(POJO)[ name:" + name + " age:" + age + "]";
}
}
Layout
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context=".MainActivity">
<ScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:id="@+id/scrollView">
<TextView
android:id="@+id/txtMsg"
android:text="Hello World!"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</ScrollView>
</LinearLayout>
Manifest
Remember to add permission clause
<uses-permission android:name="android.permission.INTERNET" />
GSON API
Use Windows-Explorer. Place a copy of the latest gson jar in the application’s app/libs
Your Gradle Scripts/build.gradle(Module:app) file needs to be modified to include references to the GSON API. In our example we have:
...
dependencies {
compile 'com.android.support:support-v4:19.1.0'
compile files('libs/gson-2.2.4.jar')
}
PHP Code to create “westerosLadies.txt” file
<?php
//make disk file holding a
$person0 = array('name' =>
$person1 = array('name' =>
$person2 = array('name' =>
JSON encoded list
'Daenerys', 'age'
'Arya',
'age'
'Cersei',
'age'
of
=>
=>
=>
Person objects
20);
12);
35);
$people = array($person0, $person1, $person2);
$jsondata = json_encode($people);
echo "<p>JSON Encoded Data <br>" . $jsondata;
$myfile = fopen("westerosLadiesJson.txt", "w") or die("Unable to open file!");
fwrite($myfile, $jsondata);
fclose($myfile);
echo '<br>' . 'Done writing file...';
?>
PHP code: getPersonNoSql.php (return a JSON string with heroes listed by castle)
<?php
// METHOD: getPeopleNoSql.php
// retrieves people by castle location (eg.?castle=winterfell)
// data comes from comes from associative arrays (noSql)
// --------------------------------------------------------------// create anonymous Person-like objects
$person0 = array('name' => 'Cersei Lannister', 'age' => 40);
$person1 = array('name' => 'Tiryion Lannister', 'age' => 30);
$person2 = array('name' => 'Arya Stark', 'age' => 11);
$person3 = array('name' => 'Jon Snow', 'age' => 20);
$person4 = array('name' => 'Hodor', 'age' => 40);
$person5 = array('name' => 'Daenerys Targaryen', 'age' => 18);
// create lists of people-by-HomeCastle
$winterfelPeople = array($person2, $person3,$person4);
$kingsLandingPeople = array($person0, $person1);
$dragonstonePeople = array($person5);
$people = array($person0, $person1, $person2, $person3,$person4, $person5);
// select what list to return (only winterfel in this example)
if( strtolower($_REQUEST['castle']) == 'winterfell' )
$people = $winterfelPeople;
else if ( strtolower($_REQUEST['castle']) == 'kings_landing' )
$people = $kingsLandingPeople;
else if ( strtolower($_REQUEST['castle']) == 'dragonstone' )
$people = $dragonstonePeople;
// respond with JSON-encoded list
echo json_encode($people);
?>