Microstrategy: A 9‑5‑Friendly Foreign Tech Company with Strong Java Interview Process

System design & data sync

Using Domain‑Driven Design (DDD) the system is split into five core services:

User Center – authentication and authorization

Course Center – course management and search

Media Center – video upload and transcoding

Order‑Payment Center – payment and subscription handling

Notification Center – asynchronous messaging

Canal sync MySQL → Elasticsearch

Canal works by mimicking a MySQL slave:

伪装成从库 (Slave) – Canal sends a handshake identical to a real MySQL slave and is accepted as a replica.

订阅 Binlog – After authentication, MySQL pushes binary logs (INSERT, UPDATE, DELETE) from the configured position (Position or GTID) to Canal.

解析与投递 – Canal parses the raw binlog into a structured format (e.g., JSON) and publishes the change events to a message queue such as Kafka or RocketMQ. Downstream consumers read the events and write them into Elasticsearch.

Data inconsistency handling

Three‑layer safeguard:

监控告警 – Monitor Canal consumption lag (Position) and trigger alerts when delay exceeds a threshold.

定期对账 – A scheduled script runs during low‑traffic windows (e.g., nightly) to sample or fully compare core data between MySQL and Elasticsearch, logging any discrepancies.

手动/自动修复 – Small mismatches are fixed with ad‑hoc scripts; large mismatches are resolved by a full‑sync job executed in the off‑peak period.

Video transcoding with XXL‑Job

Task states stored in the database:

UPLOADING   // 上传中
UPLOADED    // 上传完成 / 待转码
TRANSCODING // 转码中
SUCCESS     // 转码成功
FAIL        // 转码失败

Workflow:

Job triggers and sets state to TRANSCODING.

On success, the transcoded video URLs are written back and state is updated to SUCCESS.

If the process fails or the server crashes, the state remains TRANSCODING.

A compensating XXL‑Job scans long‑running TRANSCODING tasks, retries them, or marks them as FAIL, guaranteeing eventual consistency.

Redis

Redis is an open‑source, in‑memory NoSQL key‑value store written in C (BSD license). It provides fast read/write, persistence options, and native data types such as String, Hash, Sorted Set, Bitmap, HyperLogLog, and GEO. Advanced features include transactions, Lua scripting, pub/sub, and clustering solutions (Sentinel, Cluster).

MongoDB

MongoDB is a distributed document‑oriented database written in C++. It stores data as BSON documents (JSON‑like) and supports schema‑less modeling. Key capabilities are horizontal scaling via sharding, high availability, and rich indexing (single‑field, compound, hashed, text, geospatial). The flexible data model and scalable architecture make it suitable for high‑load web applications.

SQL injection

Typical vulnerable code concatenates user input directly into the SQL string:

String sql = "SELECT * FROM users WHERE username = '" + username + "' AND password = '" + password + "'";

Input admin' -- turns the query into:

SELECT * FROM users WHERE username = 'admin' -- ' AND password = '...irrelevant...'

The -- comment operator disables the password check, allowing login bypass.

Defence: use prepared statements (e.g., PreparedStatement in Java or #{} placeholders in MyBatis) to separate SQL syntax from data, and validate user input.

Java exception taxonomy

Checked exceptions must be declared or caught (e.g., IOException, ClassNotFoundException, SQLException).

Unchecked exceptions are subclasses of RuntimeException and need not be declared. Common examples: NullPointerException – null reference access IllegalArgumentException – illegal method argument NumberFormatException – invalid number format (subclass of IllegalArgumentException) ArrayIndexOutOfBoundsException – array index out of range ClassCastException – invalid type cast ArithmeticException – arithmetic error (e.g., divide by zero) SecurityException – security manager violation UnsupportedOperationException – operation not supported

Object‑oriented fundamentals

Encapsulation

Hide internal state behind methods. Example:

public class Student {
    private int id; // id属性私有化
    private String name; // name属性私有化

    // 获取id的方法
    public int getId() { return id; }
    // 设置id的方法
    public void setId(int id) { this.id = id; }
    // 获取name的方法
    public String getName() { return name; }
    // 设置name的方法
    public void setName(String name) { this.name = name; }
}

Inheritance

A subclass inherits all members of its superclass (private members are inherited but not directly accessible). Subclasses can add new fields/methods or override existing ones.

Polymorphism

Superclass references can point to subclass instances. Method dispatch is determined at runtime; overridden methods in the subclass are executed. IDE coding tasks Binary‑tree inorder traversal – both recursive and iterative implementations. Tree‑based scoring problem – compute the maximum score after performing operations on a tree. Intelligence puzzles 25‑horse race problem Goal: find the top three horses using the minimum number of races when only relative ordering is known. Divide 25 horses into 5 groups (A‑E) and race each group (5 races). Race the winners of each group (1 race) to rank groups as A, B, C, D, E. Potential candidates for 2nd and 3rd place are: A2, A3, B1, B2, C1 (5 horses). Race these 5 horses (1 race). The top two in this race are the overall 2nd and 3rd. Total races = 5 + 1 + 1 = 7 . Gold‑bar payment problem Cut the bar twice to obtain pieces of 1/7, 2/7, and 4/7 of the whole. Pay each day as follows: Day 1: give 1/7. Day 2: give 2/7 and take back 1/7 (net 1/7). Day 3: give 1/7 (total 3/7). Day 4: give 4/7 and take back 1/7 + 2/7 (net 1/7, total 4/7). Day 5: give 1/7 (total 5/7). Day 6: give 2/7 and take back 1/7 (net 1/7, total 6/7). Day 7: give 1/7 (total 7/7).