Java MySQL动态语句编写实现方式

public List<User> findUsers(String name, Integer age, String email) {
    Connection conn = null;
    PreparedStatement stmt = null;
    ResultSet rs = null;
    List<User> users = new ArrayList<>();
    try {
        conn = dataSource.getConnection();
        // 基础SQL
        StringBuilder sql = new StringBuilder("SELECT * FROM users WHERE 1=1");
        // 动态添加条件
        List<Object> params = new ArrayList<>();
        if (name != null) {
            sql.append(" AND name = ?");
            params.add(name);
        }
        if (age != null) {
            sql.append(" AND age = ?");
            params.add(age);
        }
        if (email != null) {
            sql.append(" AND email LIKE ?");
            params.add("%" + email + "%");
        }
        stmt = conn.prepareStatement(sql.toString());
        // 设置参数
        for (int i = 0; i < params.size(); i++) {
            stmt.setObject(i + 1, params.get(i));
        }
        rs = stmt.executeQuery();
        while (rs.next()) {
            User user = new User();
            user.setId(rs.getInt("id"));
            user.setName(rs.getString("name"));
            user.setAge(rs.getInt("age"));
            user.setEmail(rs.getString("email"));
            users.add(user);
        }
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        // 关闭资源
    }
    return users;
}

public List<User> findUsers(String name, Integer age, String email) {
    CriteriaBuilder cb = entityManager.getCriteriaBuilder();
    CriteriaQuery<User> query = cb.createQuery(User.class);
    Root<User> root = query.from(User.class);
    List<Predicate> predicates = new ArrayList<>();
    if (name != null) {
        predicates.add(cb.equal(root.get("name"), name));
    }
    if (age != null) {
        predicates.add(cb.equal(root.get("age"), age));
    }
    if (email != null) {
        predicates.add(cb.like(root.get("email"), "%" + email + "%"));
    }
    query.where(predicates.toArray(new Predicate[0]));
    return entityManager.createQuery(query).getResultList();
}

public List<User> findUsers(String name, Integer age, String email) {
    return userRepository.findAll((root, query, cb) -> {
        List<Predicate> predicates = new ArrayList<>();
        if (name != null) {
            predicates.add(cb.equal(root.get("name"), name));
        }
        if (age != null) {
            predicates.add(cb.equal(root.get("age"), age));
        }
        if (email != null) {
            predicates.add(cb.like(root.get("email"), "%" + email + "%"));
        }
        return cb.and(predicates.toArray(new Predicate[0]));
    });
}

public interface UserMapper {
    List<User> findUsers(@Param("name") String name, 
                        @Param("age") Integer age, 
                        @Param("email") String email);
}

<select id="findUsers" resultType="User">
    SELECT * FROM users
    <where>
        <if test="name != null">
            AND name = #{name}
        </if>
        <if test="age != null">
            AND age = #{age}
        </if>
        <if test="email != null">
            AND email LIKE CONCAT('%', #{email}, '%')
        </if>
    </where>
</select>

public List<User> findUsers(String name, Integer age, String email) {
    QueryWrapper<User> queryWrapper = new QueryWrapper<>();
    if (name != null) {
        queryWrapper.eq("name", name);
    }
    if (age != null) {
        queryWrapper.eq("age", age);
    }
    if (email != null) {
        queryWrapper.like("email", email);
    }
    return userMapper.selectList(queryWrapper);
}

public List<User> findUsers(String name, Integer age, String email) {
    return dslContext.selectFrom(USERS)
        .where(name == null ? noCondition() : USERS.NAME.eq(name))
        .and(age == null ? noCondition() : USERS.AGE.eq(age))
        .and(email == null ? noCondition() : USERS.EMAIL.like("%" + email + "%"))
        .fetchInto(User.class);
}