we3j简介
we3j是提供了一个java访问以太坊网络的接口。借助we3j我们可以操作以太坊网络，包括创建账户、创建合约、执行合约、交易、查询余额、转账都可以。
项目地址https://github.com/web3j/web3j
移动app怎么和以太坊区块链直接交互?
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#######android app怎么和以太坊区块链直接交互
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android<----->web3j<----->web3<---
-->JSON-RPC<-----> Ethereum blockchain<----->smart contrats
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#######ios app怎么和以太坊区块链直接交互
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ios<----->web3swift<----->web3<----->JSON-RPC<--
---> Ethereum blockchain<----->smart contrats
你需要知道这些
如何申请一个测试环境的以太坊账户、钱包怎么使用、怎么部署合约、Metamask的使用
https://duvalcc.github.io/2018/01/12/Rospten-%E4%BB%A5%E5%A4%AA%E5%9D%8A%E6%B5%8B%E8%AF%95%E7%BD%91%E7%BB%9C%E7%9A%84%E4%BD%BF%E7%94%A8/
怎么编译智能合约到java格式?
https://www.cnblogs.com/hongpxiaozhu/p/8581002.html
android怎么和智能合约交互
https://blog.jayway.com/2017/08/23/interacting-with-ethereum-smart-contracts-from-android/
android demo下载
https://github.com/linuxhsj/AndroidWeb3jEthereum
代码说明
privateKeyRopsten 是什么?这是钱包私钥！是的、我把自己测试环境的私钥告诉你们了。怎创建的？我安装了Metamask后创建一个账号然后导出私钥的。如果要换成自己的私钥的话，你可以去你的钱包复制出你的私钥就可以了。
greeterContractAddressRopsten 是什么？这个就是合约的以太坊地址。如果你要使用你的合约，你可以先通过https://remix.ethereum.org创建你的合约、然后部署到以太坊上。然后找到你合约地址替换就好。具体可以参考https://duvalcc.github.io/Rospten-%E4%BB%A5%E5%A4%AA%E5%9D%8A%E6%B5%8B%E8%AF%95%E7%BD%91%E7%BB%9C%E7%9A%84%E4%BD%BF%E7%94%A8/2018/01/12/
ropstenUrl又是什么？这个是在infura上申请的一个key。区块链需要节点来挖矿、来跑交易、来确认交易对不对，但是呢全节点需要下载很多区块数据，你要去下载也可以，你可以使用mist钱包或者以太坊钱包，但是需要下载很多数据，需要很久才可以下载完。infura提供一种服务、让你可以访问云端的节点、就是说我们不用下载所有的区块数据了，我们通过infura可以直接连接到全节点。我们只要关注于怎么和以太坊交互就好了。要换成你自己的key话你可以去这里https://infura.io/signup注册自己的账号。
package com.example.noev.greeter;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.SeekBar;
import android.widget.TextView;
import android.widget.Toast;
import org.web3j.abi.datatypes.Utf8String;
import org.web3j.crypto.Credentials;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.Web3jFactory;
import org.web3j.protocol.core.methods.response.TransactionReceipt;
import org.web3j.protocol.infura.InfuraHttpService;
import java.math.BigInteger;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
/**
* Main Ethereum Network
* https://mainnet.infura.io/[your-token]
*
* Test Ethereum Network (Ropsten)
* https://ropsten.infura.io/[your-token]
*
* Test Rinkeby Network
* https://rinkeby.infura.io/[your-token]
*
* IPFS Gateway
* https://ipfs.infura.io
*
* IPFS RPC
* https://ipfs.infura.io:5001
*/
public class MainActivity extends AppCompatActivity {
// private final static String privateKeyRopsten = "YOUR_PRIVATE_KEY";
private final static String privateKeyRopsten = "3d12dae3ebd0406deb87a5f1b937d96ae767648ad1252bec20745729a49e3db5";
//etherscan查看合约https://ropsten.etherscan.io/address/0x024b64940518779068e57352F3bDDdE08E4D9c40
private final static String greeterContractAddressRopsten = "0x024b64940518779068e57352F3bDDdE08E4D9c40";
// private final static String ropstenUrl = "https://ropsten.infura.io/YOUR_API_KEY";
private final static String ropstenUrl = "https://ropsten.infura.io/344WiX6NRUEc1PgSS93M";
private ProgressBar progressBar;
private EditText editText;
private TextView greetingTextView;
private TextView gasPriceTextView;
private TextView gasLimitTextView;
private SeekBar gasPriceSeekBar;
private Web3j web3j;
private Credentials credentials = Credentials.create(privateKeyRopsten);
private int minimumGasLimit = 21000;
private BigInteger gasLimit = new BigInteger(String.valueOf(minimumGasLimit));
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initUi();
setGasPriceText(10);
setGasLimit(minimumGasLimit);
initWeb3j();
}
private void initUi() {
progressBar = (ProgressBar) findViewById(R.id.progressbar);
editText = (EditText) findViewById(R.id.edit_text);
greetingTextView = (TextView) findViewById(R.id.text);
Button readButton = (Button) findViewById(R.id.button);
readButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
getGreeting();
}
});
Button writeButton = (Button) findViewById(R.id.write_button);
writeButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
writeGreetingToContract();
}
});
gasPriceSeekBar = (SeekBar) findViewById(R.id.gas_price_seek_bar);
gasPriceSeekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
setGasPriceText(progress);
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
}
});
SeekBar gasLimitSeekBar = (SeekBar) findViewById(R.id.gas_limit_seek_bar);
gasLimitSeekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
@Override
public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
setGasLimit(progress + minimumGasLimit);
}
@Override
public void onStartTrackingTouch(SeekBar seekBar) {
}
@Override
public void onStopTrackingTouch(SeekBar seekBar) {
}
});
gasLimitTextView = (TextView) findViewById(R.id.gas_limit_text_view);
gasPriceTextView = (TextView) findViewById(R.id.gas_price_text_view);
}
private void writeGreetingToContract() {
progressBar.setVisibility(View.VISIBLE);
WriteTask writeTask = new WriteTask();
writeTask.execute(editText.getText().toString());
}
private void getGreeting() {
try {
progressBar.setVisibility(View.VISIBLE);
ReadTask readTask = new ReadTask();
readTask.execute();
} catch (Exception e) {
Log.d("wat", "getGreeting exception = " + e.getMessage());
}
}
private void initWeb3j() {
InitWeb3JTask task = new InitWeb3JTask();
task.execute(ropstenUrl);
}
public void setGasPriceText(int gasPrice) {
String formattedString = getString(R.string.gas_price, String.valueOf(gasPrice));
gasPriceTextView.setText(formattedString);
}
private BigInteger getGasPrice() {
int gasPriceGwei = gasPriceSeekBar.getProgress();
BigInteger gasPriceWei = BigInteger.valueOf(gasPriceGwei + 1000000000L);
Log.d("wat", "getGasPrice: " + String.valueOf(gasPriceGwei));
return gasPriceWei;
}
public void setGasLimit(int gasLimit) {
String gl = String.valueOf(gasLimit);
this.gasLimit = new BigInteger(gl);
gasLimitTextView.setText(getString(R.string.gas_limit, gl));
}
private class ReadTask extends AsyncTask {
@Override
protected String doInBackground(String... params) {
String result;
try {
Greeter greeter = Greeter.load(greeterContractAddressRopsten, web3j, credentials, getGasPrice(), gasLimit);
Future greeting = greeter.greet();
Utf8String greetingUtf8 = greeting.get();
result = greetingUtf8.getValue();
} catch (Exception e) {
result = "Error reading the smart contract. Error: " + e.getMessage();
}
return result;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
progressBar.setVisibility(View.INVISIBLE);
greetingTextView.setText(result);
}
}
private class WriteTask extends AsyncTask {
@Override
protected String doInBackground(String... params) {
String greetingToWrite = params[0];
String result;
try {
Greeter greeter = Greeter.load(greeterContractAddressRopsten, web3j, credentials, getGasPrice(), gasLimit);
TransactionReceipt transactionReceipt = greeter.changeGreeting(new Utf8String(greetingToWrite)).get(3, TimeUnit.MINUTES);
result = "Successful transaction. Gas used: " + transactionReceipt.getGasUsed();
} catch (Exception e) {
result = "Error during transaction. Error: " + e.getMessage();
}
return result;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
progressBar.setVisibility(View.INVISIBLE);
Toast.makeText(MainActivity.this, result, Toast.LENGTH_LONG).show();
}
}
private class InitWeb3JTask extends AsyncTask {
@Override
protected String doInBackground(String... params) {
String url = params[0];
InfuraHttpService infuraHttpService;
String result = "Success initializing web3j/infura";
try {
infuraHttpService = new InfuraHttpService(url);
web3j = Web3jFactory.build(infuraHttpService);
} catch (Exception wtf) {
String exception = wtf.toString();
Log.d("wat", "Error initializing web3j/infura. Error: " + exception);
}
return result;
}
@Override
protected void onPostExecute(String result) {
super.onPostExecute(result);
Toast.makeText(MainActivity.this, result, Toast.LENGTH_LONG).show();
}
}
}
合约solidity源码greeter.sol
contract greeter is mortal {
/* define variable greeting of the type string */
string greeting;
/* this runs when the contract is executed */
function greeter(string _greeting) public {
greeting = _greeting;
}
/* change greeting */
function changeGreeting(string _greeting) public {
greeting = _greeting;
}
/* main function */
function greet() constant returns (string) {
return greeting;
}
}
Greeter 是合约部分(这是由greeter.sol编译后生成的)
etherscan上查看这个合约https://ropsten.etherscan.io/address/0x024b64940518779068e57352F3bDDdE08E4D9c40
package com.example.noev.greeter;
import java.math.BigInteger;
import java.util.Arrays;
import java.util.Collections;
import java.util.concurrent.Future;
import org.web3j.abi.FunctionEncoder;
import org.web3j.abi.TypeReference;
import org.web3j.abi.datatypes.Function;
import org.web3j.abi.datatypes.Type;
import org.web3j.abi.datatypes.Utf8String;
import org.web3j.crypto.Credentials;
import org.web3j.protocol.Web3j;
import org.web3j.protocol.core.methods.response.TransactionReceipt;
import org.web3j.tx.Contract;
import org.web3j.tx.TransactionManager;
/**
* Auto generated code.
* Do not modify!
* Please use {@link org.web3j.codegen.SolidityFunctionWrapperGenerator} to update.
*
* Generated with web3j version 2.2.1.
*/
public final class Greeter extends Contract {
private static final String BINARY = "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";
private Greeter(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
super(BINARY, contractAddress, web3j, credentials, gasPrice, gasLimit);
}
private Greeter(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
super(BINARY, contractAddress, web3j, transactionManager, gasPrice, gasLimit);
}
public Future kill() {
Function function = new Function("kill", Arrays.asList(), Collections.>emptyList());
return executeTransactionAsync(function);
}
public Future greet() {
Function function = new Function("greet",
Arrays.asList(),
Arrays.>asList(new TypeReference() {}));
return executeCallSingleValueReturnAsync(function);
}
public Future changeGreeting(Utf8String _greeting) {
Function function = new Function("changeGreeting", Arrays.asList(_greeting), Collections.>emptyList());
return executeTransactionAsync(function);
}
public static Future deploy(Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit, BigInteger initialWeiValue, Utf8String _greeting) {
String encodedConstructor = FunctionEncoder.encodeConstructor(Arrays.asList(_greeting));
return deployAsync(Greeter.class, web3j, credentials, gasPrice, gasLimit, BINARY, encodedConstructor, initialWeiValue);
}
public static Future deploy(Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit, BigInteger initialWeiValue, Utf8String _greeting) {
String encodedConstructor = FunctionEncoder.encodeConstructor(Arrays.asList(_greeting));
return deployAsync(Greeter.class, web3j, transactionManager, gasPrice, gasLimit, BINARY, encodedConstructor, initialWeiValue);
}
public static Greeter load(String contractAddress, Web3j web3j, Credentials credentials, BigInteger gasPrice, BigInteger gasLimit) {
return new Greeter(contractAddress, web3j, credentials, gasPrice, gasLimit);
}
public static Greeter load(String contractAddress, Web3j web3j, TransactionManager transactionManager, BigInteger gasPrice, BigInteger gasLimit) {
return new Greeter(contractAddress, web3j, transactionManager, gasPrice, gasLimit);
}
}
依赖部分
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
compile fileTree(dir: 'libs', include: ['*.jar'])
// androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
// exclude group: 'com.android.support', module: 'support-annotations'
// })
compile 'com.android.support:appcompat-v7:26.0.0'
// compile 'com.android.support.constraint:constraint-layout:1.0.0-alpha8'
implementation 'com.android.support.constraint:constraint-layout:1.0.2'
compile 'org.web3j:core-android:2.2.1'
// testCompile 'junit:junit:4.12'
}
运行说明
当你把程序放到android studio跑起来的时候、手机上可以看到get greeting和write按钮。
1、点击get greeting默认会返回hey man.
2、再输入框中你可以输入你需要修改的值，比如我输入how are you，然后点击write就是要提交以太坊上去，执行合约需要消耗eter。你需要去申请，方法参考这个https://duvalcc.github.io/Rospten-%E4%BB%A5%E5%A4%AA%E5%9D%8A%E6%B5%8B%E8%AF%95%E7%BD%91%E7%BB%9C%E7%9A%84%E4%BD%BF%E7%94%A8/2018/01/12/
3、再次点击get greeting默认会返回how are you.