Question

我的java servlet init方法无法创建mysql表 - 我想知道原因。当我直接登录到mysql并创建表时，生活是美好的，当我删除表并运行servlet时 - 没有表，servlet抛出一个异常（还没有把它挖出来）。代码看起来像这样：

package ...;
import ... // quite a bit
@WebServlet("/MyClass") 
public class MyClass extends HttpServlet {
          public void init() throws ServletException {
        try {     Foo foo = Foo.getInstance();
                    foo.createTables();  
            } catch (Exception e) {
                throw new ServletException("Error creating tables", e);         
            }
      }

... //更多MyClass的东西 } // Foo是一个看起来像这样的单身人士：

    package ...;
    import ... // quite a bit
public class Foo {
  public static final Foo INSTANCE = new Foo();

  public static Foo getInstance() {
    return INSTANCE;
  }

... //更多Foo的东西，然后

public void createTables(){
 try {

        // first establish a connection
 Connection connection = Foo.getInstance().getConnection(); // get connection est.

// est。连接到dbase - 一旦表格设置好了

 //Create a query. 
 Statement stmt = connection.createStatement(); 

    String query = "CREATE TABLE IF NOT EXISTS survey (uuid_Survey VARCHAR(36) NOT NULL, "+
    "top VARCHAR(40), " +
    " likert VARCHAR(40), "+
    " numerical VARCHAR(40), "+
    " open VARCHAR(40), " +
    " KEY ix_survey_uuid (uuid_Survey), "+
    " PRIMARY KEY (uuid_Survey))";

 ResultSet rs = stmt.executeQuery( query ); 
     query = "CREATE TABLE IF NOT EXISTS result (" +
    "uuid_Survey VARCHAR(36) NOT NULL, "+
    "remoteAddress VARCHAR(15) NOT NULL, " +
    "currentTime BIGINT NOT NULL, "+
    " likert VARCHAR(40),"+
    " numerical DOUBLE, " +
    " open VARCHAR(40),  "+
    " PRIMARY KEY (uuid_Survey, remoteAddress, currentTime),"+
    "FOREIGN KEY ix_survey_uuid (uuid_Survey) REFERENCES survey (uuid_Survey))" ;

 rs = stmt.executeQuery( query );  

 connection.close();

 } catch (Exception e) {
        System.err.println("Error creating tables: " + e);
 }

 }

Answer 1

您无法使用stmt.executeQuery( query );

正如Doc所说 -

ResultSet#executeQuery(String sql) - 此方法执行给定的SQL语句，该语句返回单个ResultSet对象。其中 sql - 要发送到数据库的SQL语句，通常是静态 SQL SELECT语句

您可能希望使用execute()代替

赞stmt.execute(query);

或

String query = "CREATE TABLE IF NOT EXISTS survey (uuid_Survey VARCHAR(36) NOT NULL,"+
        "top VARCHAR(40), " +
        " likert VARCHAR(40), "+
        " numerical VARCHAR(40), "+
        " open VARCHAR(40), " +
        " KEY ix_survey_uuid (uuid_Survey), "+
        " PRIMARY KEY (uuid_Survey))";
PreparedStatement statement = conn.prepareStatement(query);
int count = statement.executeUpdate();
if(count>=0){
    System.out.println("Successfully created.");
}

servlet init方法无法创建mysql表 - 为什么？

1 个答案: