Java8把list转为map

收集其中两个字段

public Map<Long, String> getIdNameMap(List<Account> accounts) {
    return accounts.stream().collect(Collectors.toMap(Account::getId, Account::getUsername));
}

收集对象本身

public Map<Long, Account> getIdAccountMap(List<Account> accounts) {
    return accounts.stream().collect(Collectors.toMap(Account::getId, account -> account));
}
or

public Map<Long, Account> getIdAccountMap(List<Account> accounts) {

    return accounts.stream().collect(Collectors.toMap(Account::getId, Function.identity()));
}

重复key的情况

public Map<String, Account> getNameAccountMap(List<Account> accounts) {
    return accounts.stream().collect(Collectors.toMap(Account::getUsername, Function.identity(), (key1, key2) -> key2));
}

List<Map<String,Object>>转为Map

//select id, user_name userName from....
Map<String,String> idMap = userMap.stream().collect(Collectors.toMap(a1->a1.get("id"),a2->a2.get("userName")));