java的string转换为list

Posted 2023-03-30

string类型的 string abc = "aaa,bbb,ccc"，
怎样转换为list呢

方法如下：

List<String> list = new ArrayList<String>();


list.add("a1");


list.add("a2");


String[] toBeStored = list.toArray(new String[list.size()]);


for(String s : toBeStored)


System.out.println(s);

或者是：

List<String> list = new ArrayList<String>();


list.add("a1");


list.add("a2");   


String[] toBeStored = new String[al.size()];


list.toArray(toBeStored);


for (String s : toBeStored)


System.out.println(s);

拓展资料：

Java具有简单性、面向对象、分布式、健壮性、安全性、平台独立与可移植性、多线程、动态性等特点 。Java可以编写桌面应用程序、Web应用程序、分布式系统和嵌入式系统应用程序等

Java是一门面向对象编程语言，不仅吸收了C++语言的各种优点，还摒弃了C++里难以理解的多继承、指针等概念，因此Java语言具有功能强大和简单易用两个特征。Java语言作为静态面向对象编程语言的代表，极好地实现了面向对象理论，允许程序员以优雅的思维方式进行复杂的编程。

参考技术A

import java.util.Arrays;

import java.util.List;

public class test

public static void main(String[] args)

// 字符串转list<String>

String str = "aaa,bbb,ccc";

List<String> lis = Arrays.asList(str.split(","));

for (String string : lis)

System.out.println(string);

拓展资料：

List：元素是有序的(怎么存的就怎么取出来，顺序不会乱)，元素可以重复（角标1上有个3，角标2上也可以有个3）因为该集合体系有索引；

ArrayList：底层的数据结构使用的是数组结构（数组长度是可变的百分之五十延长）（特点是查询很快，但增删较慢）线程不同步；

LinkedList：底层的数据结构是链表结构（特点是查询较慢，增删较快）；

Vector：底层是数组数据结构 线程同步（数组长度是可变的百分之百延长）。

参考技术B     String abc = "aaa,bbb,ccc";
    String[] arr = abc.split(",");
    List<String> list = java.util.Arrays.aslist(abc);

本回答被提问者采纳 参考技术C 假设String对象为stringArray；
List<T> list=JSONArray.parseArray("",T.class);
其中T为要转为的list其中的对象，比如创建的实体类。 参考技术D String[] arr= abc.split(",");
List list = Arrays.asList(arr);

无法将类型“java.lang.String”的属性值转换为属性“事务”所需的类型“java.util.List”

【中文标题】无法将类型“java.lang.String”的属性值转换为属性“事务”所需的类型“java.util.List”

【英文标题】：Failed to convert property value of type 'java.lang.String' to required type 'java.util.List' for property 'transactions'

【发布时间】：2021-10-27 17:30:35

【问题描述】：

我正在使用 thymeleaf 并在将数据从 String 转换为 List 时遇到一些错误。在这里我附上了我的代码

我的实体类：

@Entity
@Table(name="customer")
public class Customer 
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int id;

@Column(name = "first_name")
@NotNull(message = "First Name cannot be empty")
@Size(min = 1, message = "First Name cannot be empty")
private String firstName;

@Column(name = "last_name")
@NotNull(message = "Last Name cannot be empty")
@Size(min = 1, message = "Last Name cannot be empty")
private String lastName;

@Column(name = "email")
@NotNull(message = "Email ID cannot be empty")
@Pattern(regexp = "^[a-zA-Z0-9.+_-]+@[a-zA-Z0-9.-]+$",
        message = "Enter valid mail id")
private String email;

@Column(name = "branch")
@NotNull(message = "Branch name cannot be empty")
private String branch;

@Column(name = "balance")
private double balance;

@OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY)
@JoinColumn(name = "customer_id")
private List<Transaction> transactions;

public Customer(String firstName, String lastName, String email, String branch, double balance) 
    this.firstName = firstName;
    this.lastName = lastName;
    this.email = email;
    this.branch = branch;
    this.balance = balance;


public Customer() 


public int getId() 
    return id;


public void setId(int id) 
    this.id = id;


public String getFirstName() 
    return firstName;


public void setFirstName(String firstName) 
    this.firstName = firstName;


public String getLastName() 
    return lastName;


public void setLastName(String lastName) 
    this.lastName = lastName;


public String getEmail() 
    return email;


public void setEmail(String email) 
    this.email = email;


public String getBranch() 
    return branch;


public void setBranch(String branch) 
    this.branch = branch;


public double getBalance() 
    return balance;


public void setBalance(double balance) 
    this.balance = balance;


public List<Transaction> getTransactions() 
    return transactions;


public void setTransactions(List<Transaction> transactions) 
    this.transactions = transactions;


public void addTransaction(Transaction transaction)
    if(transaction == null) 
        transactions = new ArrayList<>();
    
    transactions.add(transaction);


@Override
public String toString() 
    return "Customer" +
            "id=" + id +
            ", firstName='" + firstName + '\'' +
            ", lastName='" + lastName + '\'' +
            ", email='" + email + '\'' +
            ", branch='" + branch + '\'' +
            ", balance=" + balance +
            '';
  


@Entity
@Table(name = "transactions")
public class Transaction 
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id")
private int id;

@Column(name = "transaction")
private double amount;

public Transaction() 


public Transaction(double amount) 
    this.amount = amount;


public int getId() 
    return id;


public void setId(int id) 
    this.id = id;


public double getAmount() 
    return amount;


public void setAmount(double amount) 
    this.amount = amount;


@Override
public String toString() 
    return "Transaction" +
            "id=" + id +
            ", amount=" + amount +
            '';

控制器：

@Controller
@RequestMapping("/customers")
public class CustomerController 
@Autowired
private CustomerRestService customerRestService;

public static String username;
public static Object password;

public CustomerController() 


@GetMapping("/list")
public String listCustomers(Model model, @CurrentSecurityContext(expression = "authentication")Authentication authentication) 
    username = authentication.getName();
    password = authentication.getCredentials();
    List<Customer> customers = customerRestService.getCustomerList();

    model.addAttribute("customers", customers);

    return "list-customers";


@GetMapping("/showFormToAddCustomer")
public String showFormToAddCustomer(Model model) 
    Customer customer = new Customer();
    model.addAttribute("customer", customer);
    return "customer-form";


@PostMapping("/saveCustomer")
public String saveCustomer(@ModelAttribute("customer") Customer customer) 
    System.out.println("\n" + customer);
    System.out.println(customer.getTransactions());
    customerRestService.saveCustomer(customer);
    return "redirect:/customers/list";


@GetMapping("/showFormToUpdateCustomer")
public String showformForUpdate(@RequestParam("customerId") int id,
                                Model model) 
    Customer customer = customerRestService.findCustomerById(id);
    System.out.println(customer);
    System.out.println(customer.getTransactions());
    
    model.addAttribute("customer", customer);
    
    return "customer-form";

服务：

@Service
public class CustomerRestServiceImple implements CustomerRestService
private RestTemplate restTemplate;

private String restUrl;

@Autowired
public CustomerRestServiceImple(RestTemplate restTemplate,
                                @Value("$crm.rest.url") String restUrl) 
    this.restTemplate = restTemplate;
    this.restUrl = restUrl;


private HttpHeaders httpHeaders() 
    String username = CustomerController.username;
    Object password = CustomerController.password;

    String plainCreds = username+":"+password.toString();
    byte[] plainCredsBytes = plainCreds.getBytes();
    byte[] base64CredsBytes = Base64.encodeBase64(plainCredsBytes);
    String base64Creds = new String(base64CredsBytes);

    HttpHeaders headers = new HttpHeaders();
    headers.add("Authorization", "Basic " + base64Creds);
    headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
    headers.setContentType(MediaType.APPLICATION_JSON);
    //HttpEntity<String> request = new HttpEntity<String>(headers);
    return headers;


@Override
public List<Customer> getCustomerList() 
    HttpEntity<String> request = new HttpEntity<>(httpHeaders());

    ResponseEntity<List<Customer>> responseEntity = restTemplate.exchange(restUrl, HttpMethod.GET, request,
            new ParameterizedTypeReference<List<Customer>>() );

    List<Customer> customers = responseEntity.getBody();

    return customers;


@Override
public Customer findCustomerById(int id) 
    //Customer customer = restTemplate.getForObject(restUrl + "/" + id, Customer.class);
    HttpEntity<String> request = new HttpEntity<>(httpHeaders());
    ResponseEntity<Customer> responseEntity = restTemplate.exchange(restUrl + "/" + id, HttpMethod.GET, request, Customer.class);
    Customer customer = responseEntity.getBody();
    return customer;


@Override
public void saveCustomer(Customer customer) 
    System.out.println("\n" + customer);
    System.out.println(customer.getTransactions());

    HttpEntity<Customer> request = new HttpEntity<>(customer, httpHeaders());
    int customerId = customer.getId();

    if(customerId == 0)
        restTemplate.exchange(restUrl, HttpMethod.POST, request, Customer.class);
     else 
        restTemplate.exchange(restUrl, HttpMethod.PUT, request, Customer.class);
        

HTML 表单：

    <h3>Customer Directory</h3>
    <hr>

    <p class="h4 mb-4">Save Customer</p>

    <form action="#" th:action="@/customers/saveCustomer"
          th:object="$customer" method="POST">

        <!-- Add hidden form field to handle the update -->
        <input type="hidden" th:field="*id" />

        <input type="text" th:field="*firstName"
            class="form-control mb-4 col-4" placeholder="First Name">

        <input type="text" th:field="*lastName"
               class="form-control mb-4 col-4" placeholder="Last Name">

        <input type="text" th:field="*email"
               class="form-control mb-4 col-4" placeholder="Email">

        <input type="text" th:field="*branch"
               class="form-control mb-4 col-4" placeholder="Branch">

        <input type="text" th:field="*balance"
               class="form-control mb-4 col-4" placeholder="Balance">

        <input type="text" th:field="*transactions"
               class="form-control mb-4 col-4" placeholder="Transactions">

        <!--input type="hidden" th:field="*transactions" /-->

        <button type="submit" class="btn btn-info col-2">Save</button>

    </form>

    <hr>
    <a th:href="@/customers/list">Back to Customers List</a>

</div>

错误：

字段“交易”的对象“客户”中的字段错误：拒绝值 [[Transactionid=1, amount=1000.0, Transactionid=3, amount=100.0]]；代码 [typeMismatch.customer.transactions,typeMismatch.transactions,typeMismatch.java.util.List,typeMismatch];参数 [org.springframework.context.support.DefaultMessageSourceResolvable: 代码 [customer.transactions,transactions];论据 [];默认消息[事务]]；默认消息 [；嵌套异常是 org.springframework.core.convert.ConversionFailedException：无法从类型 [java.lang.String] 转换为类型 [@javax.persistence.OneToMany @javax.persistence.JoinColumn com.kaneki.springboot.bankapplication.entity。交易] 价值 '[交易id=1, 金额=1000.0, 交易id=3, 金额=100.0]';嵌套异常是 java.lang.NumberFormatException: For input string: "[Transactionid=1, amount=1000.0, Transactionid=3, amount=100.0]"]

【参考方案1】：

在这里，您从您的 HTML 中接收作为字符串的 Transaction 字段，因此在控制器中您必须处理该字符串并从中提取 id 和金额，然后将该 id 和金额设置到交易表中。试试这个，如果你已经在你的控制器中尝试或编写了它，请分享控制器的代码。

【讨论】：

我在这里添加了控制器代码。能否请您再重新审视一下这个问题