如何捕捉以太坊合约异常？

Question

This is my simple contract

contract Test {
    /* This creates an array with all balances */
    mapping (address => uint256) public balanceOf;

    /* Initializes contract with initial supply tokens to the creator of the contract */
    function Test(
        uint256 initialSupply
        ) {
        balanceOf[msg.sender] = initialSupply;              // Give the creator all initial tokens
    }

    /* Send coins */
    function transfer(address _to, uint256 _value) {
        if (balanceOf[msg.sender] < _value) throw;           // Check if the sender has enough
        if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
        balanceOf[msg.sender] -= _value;                     // Subtract from the sender
        balanceOf[_to] += _value;                            // Add the same to the recipient
    }

function gettokenBalance(address to)constant returns (uint256){
          return balanceOf[to];
       }
}

When i am transferring tokens more than intial supply to another account the function transfer should throws exception.

How can i handle this exception and get to know transaction cannot complete.I am using web3j and calling function transfer like

Test test = Test.load(contractObj.getContractAddress(), web3j, credentials, gasprice,gaslimit);

TransactionReceipt balanceOf = test.transfer(new Address(address), transferBalance).get(); 

Answer 1

I have never used web3js but you can try using try-catch:

try{
  Test test = Test.load(contractObj.getContractAddress(), web3j, credentials, gasprice,gaslimit);

  TransactionReceipt balanceOf = test.transfer(new Address(address), transferBalance).get(); 
} catch (Exception e){
  // log you exception
}

Answer 2

How can i handle this exception and get to know transaction cannot complete

There is a single exception (a throw without arguments) in Solidity, which is "out of gas". So your "faulty" transaction is completed, however it ran out of gas. If you know the transaction hash, you can check gasLimit and gasUsed . If they are equal, your transaction has probably * ran out of gas. See more information here .

* given that you supply more than enough gas that a "correct" transaction requires.