如何用java实现数据库inner join算法，将不同list中的map关联到一行上

Question

场景：有三个List<Map>变量，现在需要根据一个输入的字符"list1.column1=list2.column2,list1.column3=list3.column4"（不是固定的）来实现inner join关系的控制，即list1中的map和list2中map通过key值column1和column2关联，同时list1中的map和list3中map通过key值column3和column4关联。在sql中就是"select * from list1 inner join list2 on list1.column1=list2.column2 inner join list3 on list1.column3=list3.column4"，将不同list中的map关联到一行上，请问要如何实现？
如果使用简单的for循环一个个处理，速度非常慢，所以需要一种更优的计算方法

Answer 1

这个可以将list1到list3看做3个表的记录。
还是要写方法循环比对的。
要循环list1里的map，复杂度为O(n*m)。

Answer 2

用list的filter试试吧（其实原理还是for）
现根据关联关系把符合条件的list1选出来，然后再遍历选出的list1把符合条件list2和list3加进选出的结果集
for examplepublic class Sample {
    public static void main(String[] args) {
        try {
            List<Map<String, Object>> list1 = new ArrayList<Map<String, Object>>() {{ //假设各个list的数据
                add(new HashMap<String, Object>() {{
                    put("column11", 1);
                    put("column12", 2);
                    put("column13", 3);
                }});
                add(new HashMap<String, Object>() {{
                    put("column11", 1);
                    put("column12", 12);
                    put("column13", 13);
                }});
                add(new HashMap<String, Object>() {{
                    put("column11", 21);
                    put("column12", 22);
                    put("column13", 23);
                }});
            }};
            List<Map<String, Object>> list2 = new ArrayList<Map<String, Object>>() {{
                add(new HashMap<String, Object>() {{
                    put("column21", 1);
                    put("column22", 2);
                    put("column23", 3);
                }});
                add(new HashMap<String, Object>() {{
                    put("column21", 11);
                    put("column22", 1);
                    put("column23", 13);
                }});
                add(new HashMap<String, Object>() {{
                    put("column21", 21);
                    put("column22", 22);
                    put("column23", 23);
                }});
            }};
            List<Map<String, Object>> list3 = new ArrayList<Map<String, Object>>() {{
                add(new HashMap<String, Object>() {{
                    put("column31", 1);
                    put("column32", 2);
                    put("column34", 33);
                }});
                add(new HashMap<String, Object>() {{
                    put("column31", 11);
                    put("column32", 12);
                    put("column34", 33);
                }});
                add(new HashMap<String, Object>() {{
                    put("column31", 21);
                    put("column32", 22);
                    put("column34", 3);
                }});
            }};
            //选出符合条件的list1
            List<Map<String, Object>> result = list1.stream()
                    .filter( //是否存在list2的column2==list1.column1
                        m->
                        list2.stream()
                            .filter(
                                mm->mm.get("column22").equals(m.get("column11"))
                            )
                            .findAny()
                            .isPresent()      
                    )
                    .filter(//是否存在list3的column4==list1.column3
                            m->
                            list3.stream()
                                .filter(
                                    mm->mm.get("column34").equals(m.get("column13"))
                                )
                                .findAny()
                                .isPresent()
                    )
                    .collect(Collectors.toList());
            //在选出符合条件的list1的基础上，把符合条件的list2，list3加入结果集
            result.forEach(m->{
                Map<String, Object> obj = list2.stream().filter(mm->mm.get("column22").equals(m.get("column11"))).findFirst().get();
                for (Map.Entry<String, Object> o : obj.entrySet()) {
                    m.put(o.getKey(), o.getValue());
                }
                obj = list3.stream().filter(mm->mm.get("column34").equals(m.get("column13"))).findFirst().get();
                for (Map.Entry<String, Object> o : obj.entrySet()) {
                    m.put(o.getKey(), o.getValue());
                }
            });
            //打印结果
            result.forEach(m->System.out.printf("%s\n", m));
            
        } catch (Throwable e) {
            e.printStackTrace();
        }
    }
}