[Blockchain] Ethereum web3j for java configuration and use <1>

Ethereum web3j for java configuration and use <1>

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Official website: here

Environment: mac & android studio

1. Import package

在app/build.gradle中：compile 'org.web3j:core:3.0.1-android'

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which is:

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'org.web3j:core:3.0.1-android'
    compile 'com.android.support:appcompat-v7:26.+'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    testCompile 'junit:junit:4.12'
    compile files('libs/android-json-rpc-0.3.4.jar')
}

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Then sync it.

2. Start the private chain

Build: here

启动：geth --rpcapi personal,db,eth,net,web3 --rpc --rinkeby console 2>>geth.log

//这里备注一下我的启动方式
geth --identity "linoy" --rpc --rpccorsdomain "*" --datadir "./" --port "30303" --nodiscover --rpcapi "personal,db,eth,net,web3,miner" --networkid 1999 console 2>>geth.log

查看：tail -f geth.log

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3. Preliminary attempt

Web3j web3 = Web3jFactory.build(new HttpService());
Web3ClientVersion web3ClientVersion = web3.web3ClientVersion().sendAsync().get();
String clientVersion = web3ClientVersion.getWeb3ClientVersion();

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Errors may occur:

Error:Execution failed for task ':app:transformResourcesWithMergeJavaResForDebug'.
> com.android.build.api.transform.TransformException: com.android.builder.packaging.DuplicateFileException: Duplicate files copied in APK META-INF/LICENSE
    File1: /Users/pro/.gradle/caches/modules-2/files-2.1/com.fasterxml.jackson.core/jackson-annotations/2.8.0/45b426f7796b741035581a176744d91090e2e6fb/jackson-annotations-2.8.0.jar
...

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solution:

The operation is successful, the errors that may occur when calling:

    Failed to connect to localhost/127.0.0.1:8548

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Reason: The emulator regards 127.0.0.1 and localhost as itself by default. On the emulator, 10.0.2.2 can be used instead of 127.0.0.1 and localhost

Solution: set the access ip to 10.0.2.2

String url = "http://10.0.2.2:8545";
Web3j web3 = Web3jFactory.build(new HttpService(url));

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