I'm assuming the method of the functional interface implemented by this lambda expression has a return value, so when using brackets, it should include a return statement, just like any method with non-void return type.

new JdbcTemplate(new SingleConnectionDataSource(c, true))
    .query("select id, name from PLAYERS", (rs, rowNum) ->
        {
            return new Player(rs.getString("id"), rs.getString("name");
        }) 
    );

WARNING
As mentioned in comments, Using peek() for production code is considered bad practice
The reasson is that "According to its JavaDocs, the intermediate Stream operation java.util.Stream.peek() “exists mainly to support debugging” purposes."
As a consequence, this proposed solution SHOULD NOT be used.

Forgot to relate to the first code snippet. I wouldn't use forEach at all. Since you are collecting the elements of the Stream into a List, it would make more sense to end the Stream processing with collect. Then you would need peek in order to set the ID.

List<Entry> updatedEntries = 
    entryList.stream()
             .peek(e -> e.setTempId(tempId))
             .collect (Collectors.toList());

For the second snippet, forEach can execute multiple expressions, just like any lambda expression can :

entryList.forEach(entry -> {
  if(entry.getA() == null){
    printA();
  }
  if(entry.getB() == null){
    printB();
  }
  if(entry.getC() == null){
    printC();
  }
});

However (looking at your commented attempt), you can't use filter in this scenario, since you will only process some of the entries (for example, the entries for which entry.getA() == null) if you do.

It seems you are asking how to pass t + " Twice is : " + t*2 + " , " to a method reference. You can't pass explicit parameters to method references, and you can't combine method references with lambda expressions.

You could use a Stream pipeline to first map t whatever you wish to print for each value of t, and than use a forEach with method reference to print it :

list.stream().map(t -> t + "  Twice is : " + t*2 + "  , ").forEach(System.out::print);