Java 8 Stream Operatinos

// Extract a specific property list from a collection
List<String> taskIds = taskList.stream().map(TaskItem::getTaskId).collect(Collectors.toList());

// Group collection elements by an attribute (key: attribute value, value: sub-list)
Map<String, List<UserProfile>> userOrgGroups = 
    userProfiles.stream().collect(Collectors.groupingBy(UserProfile::getOrgId));

// Group and map to single element per key (handle duplicates by taking later value)
Map<String, Product> productMap = 
    products.stream().collect(Collectors.toMap(Product::getSku, Function.identity(), (oldVal, newVal) -> newVal));

// Filter elements matching a condition (score ≥ 85)
List<UserProfile> topUsers = 
    userProfiles.stream().filter(user -> user.getScore() >= 85).collect(Collectors.toList());

// Find the element with the maximum attribute value
Optional<UserProfile> maxScoreUser = 
    userProfiles.stream().max(Comparator.comparing(UserProfile::getScore));
UserProfile topUser = maxScoreUser.orElseThrow(NoSuchElementException::new);

// Check if any element has status not 1 or 2
boolean hasInvalidStatus = taskList.stream().anyMatch(task -> task.getStatusId() != 1 && task.getStatusId() != 2);

// Check if all elements have status 3
boolean allCompleted = taskList.stream().allMatch(task -> task.getStatusId() == 3);

// Multi-attribute sorting (ascending: result code → template ID → create time)
List<AuditLog> sortedLogs = 
auditLogs.stream()
    .sorted(Comparator.comparing(AuditLog::getResultCode)
        .thenComparing(AuditLog::getTemplateId)
        .thenComparing(AuditLog::getCreateTime))
    .collect(Collectors.toList());

// Manual multi-attribute sort using Collections.sort
Collections.sort(auditLogs, new Comparator<AuditLog>() {
    @Override
    public int compare(AuditLog log1, AuditLog log2) {
        long code1 = Long.parseLong(log1.getResultCode());
        long code2 = Long.parseLong(log2.getResultCode());
        int templateId1 = log1.getTemplateId();
        int templateId2 = log2.getTemplateId();
        Date time1 = log1.getCreateTime();
        Date time2 = log2.getCreateTime();

        if (code1 != code2) return code1 > code2 ? 1 : -1;
        if (templateId1 != templateId2) return templateId1 > templateId2 ? 1 : -1;
        return time1.after(time2) ? 1 : time1.before(time2) ? -1 : 0;
    }
});

// Deduplicate string list and join with comma
String mergedTime = timeSlots.stream().distinct().collect(Collectors.joining(","));

// Split comma-separated string to long list
String idString = "101,102,103,104";
List<Long> idList = Arrays.stream(idString.split(",")).map(Long::parseLong).collect(Collectors.toList());

// Convert stream to array
Integer[] intArray = Stream.of(10, 20, 30).toArray(Integer[]::new);

// Zip two lists and update properties (same length)
List<Product> updatedProducts = IntStream.range(0, sourceProducts.size())
    .mapToObj(i -> {
        Product source = sourceProducts.get(i);
        Product target = targetProducts.get(i);
        source.setCategoryId(target.getCategoryId());
        return source;
    }).collect(Collectors.toList());

JPA Relationship Configuration

@ManyToOne / @OneToMany Scenario (Dpeartment ↔ Employees)

• Tables: departments (id, name) and employees (id, name, department_id)

Department PO Class:

@Entity
@Table(name = "departments")
@ApiModel(value = "Department")
public class DepartmentPO {
    @Id
    private String id;
    @Column(name = "name")
    private String departmentName;
    
    @OneToMany(targetEntity = EmployeePO.class, cascade = {CascadeType.ALL}, fetch = FetchType.LAZY)
    @JoinColumn(name = "department_id")
    private List<EmployeePO> employees;
}

Employee PO Class:

@Entity
@Table(name = "employees")
@ApiModel(value = "Employee")
public class EmployeePO {
    @Id
    private String id;
    @Column(name = "name")
    private String employeeName;
    
    @ManyToOne(targetEntity = DepartmentPO.class, fetch = FetchType.EAGER)
    @JoinColumn(name = "department_id")
    private DepartmentPO department;
}

Employee Repository:

public interface EmployeeRepository extends JpaRepository<EmployeePO, String>, JpaSpecificationExecutor<EmployeePO> {
    List<EmployeePO> findByDepartment(DepartmentPO department);
}

Usage Example:

DepartmentPO dept = new DepartmentPO();
dept.setId("dept-001");
List<EmployeePO> deptEmployees = employeeRepository.findByDepartment(dept);

Development Issues and Solutions

1. Date Field Serialization Format

Add @JsonFormat to specify serializasion/deserialization format for Date properties.

@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss", timezone = "Asia/Shanghai")
private Date createdAt;

2. Vue Form Enter Key Triggers Page Refresh

Add @submit.native.prevent to the <el-form> tag to prevent default single-field form submission.

<el-form ref="queryForm" :model="queryParams" :inline="true" @submit.native.prevent="handleQuery">
  <el-form-item label="Keyword">
    <el-input v-model="queryParams.keyword" placeholder="Enter keyword" />
  </el-form-item>
  <el-form-item>
    <el-button type="primary" @click="handleQuery">Search</el-button>
  </el-form-item>
</el-form>

3. SQL Injection from Fuzzy Search Parameters

Escape SQL wildcards (_ and %) before constructing the LIKE clause.

String searchName = rawName.replaceAll("_", "/_").replaceAll("%", "/%");
cb.like(root.get("employeeName").as(String.class), "%" + searchName + "%");

4. Global Exception Handling

Use @RestControllerAdvice and @ExceptionHandler to centralize error handling.

@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(Exception.class)
    public ResponseEntity<ErrorResponse> handleException(Exception e) {
        log.error("Uncaught exception: {}", e.getMessage());
        
        if (e instanceof BindException) {
            String errorMsg = ((BindException) e).getAllErrors().get(0).getDefaultMessage();
            return ResponseEntity.badRequest().body(new ErrorResponse("400", errorMsg));
        } else if (e instanceof MethodArgumentTypeMismatchException) {
            return ResponseEntity.badRequest().body(new ErrorResponse("400", "Invalid parameter type"));
        }
        
        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
            .body(new ErrorResponse("500", "Internal server error"));
    }
}

5. Vue Page Cache Control

Add noCache: true to the route meta to disable caching when navigating away.

const routes = [
  {
    path: '/orders',
    component: OrdersPage,
    name: 'Orders',
    meta: {
      title: 'Orders List',
      noCache: true
    }
  }
];