Java泛型报错：T无法转换为String，Google Tink加解密代码复用问题

根因分析 #

1. 泛型方法getInformation直接将未知类型的泛型参数T赋值给boolean/double/String等具体类型变量，没有做类型转换，自然触发类型不兼容报错。
2. 逻辑错误：加密后的encryptedAccInformation栈存储的是密文字节数组，无法直接用于构造明文Account对象，原加密方法末尾调用getInformation传入加密栈属于无效逻辑。
3. API误用：Stack.empty()是判断栈是否为空的方法，返回布尔值，无法清空栈，会导致旧数据残留。

修改方案 #

1. 改造泛型getInformation方法，增加类型转换参数 #

通过传入转换函数，兼容不同类型的栈元素转字符串的需求，实现代码复用：

import java.util.function.Function;

private <T> Account getInformation(Stack<T> stack, Function<T, String> typeConverter) {
    // 直接pop不需要先peek再pop，简化代码
    boolean isApproved = Boolean.parseBoolean(typeConverter.apply(stack.pop()));
    boolean isAdmin = Boolean.parseBoolean(typeConverter.apply(stack.pop()));
    double balance = Double.parseDouble(typeConverter.apply(stack.pop()));
    String password = typeConverter.apply(stack.pop());
    String iBan = typeConverter.apply(stack.pop());
    String uuid = typeConverter.apply(stack.pop());

    return new Account(uuid, iBan, password, balance, isAdmin, isApproved);
}

2. 修正加密方法逻辑 #

// 加密方法不需要返回Account，加密后的数据存在encryptedAccInformation栈即可，可按需调整返回值
public void encrypt(Account account) throws GeneralSecurityException {
    // 清空栈用clear()，不要用empty()
    this.plaintextAccInformation.clear();
    this.encryptedAccInformation.clear();

    agjEncryption = new AesGcmJce(key.getBytes());

    this.plaintextAccInformation.push(account.getUuid());
    this.plaintextAccInformation.push(account.getIban());
    this.plaintextAccInformation.push(account.getPassword());
    this.plaintextAccInformation.push(String.valueOf(account.getBalance()));
    this.plaintextAccInformation.push(String.valueOf(account.isAdmin()));
    this.plaintextAccInformation.push(String.valueOf(account.isApproved()));

    // 去掉多余的iterator，直接判空循环即可
    while (!plaintextAccInformation.isEmpty()) {
        encryptedAccInformation.push(agjEncryption.encrypt(plaintextAccInformation.pop().getBytes(), aad.getBytes()));
    }
    // 删掉原来错误的getInformation调用，加密栈无法构造明文Account
}

3. 修正解密方法调用 #

public Account decrypt() throws GeneralSecurityException {
    this.decryptedAccInformation.clear();

    this.agjDecryption = new AesGcmJce(key.getBytes());

    while (!encryptedAccInformation.isEmpty()) {
        decryptedAccInformation.push(new String(agjDecryption.decrypt(encryptedAccInformation.pop(), aad.getBytes())));
    }
    // String类型栈传入identity函数直接返回原值即可
    return getInformation(this.decryptedAccInformation, Function.identity());
}

可选扩展：从明文栈构造Account #

如果需要直接读取明文栈生成Account，调用方式如下：

Account plainAccount = getInformation(plaintextAccInformation, Function.identity());

内容的提问来源于stack exchange，提问作者Z-100