Java ResultSet教程

Java ResultSet interface is a part of the java.sql package. It is one of the core components of the JDBC Framework. ResultSet Object is used to access query results retrieved from the relational databases.

Java ResultSet接口是java.sql包的一部分。它是JDBC框架的核心组件之一。 ResultSet对象用于访问从关系数据库检索的查询结果。

ResultSet maintains cursor/pointer which points to a single row of the query results. Using navigational and getter methods provided by ResultSet, we can iterate and access database records one by one. ResultSet can also be used to update data.

ResultSet维护指向查询结果的单行的光标/指针。使用ResultSet提供的导航和获取方法，我们可以一个一个地迭代和访问数据库记录。 ResultSet也可以用于更新数据。

Java ResultSet层次结构 (Java ResultSet Hierarchy)

The above diagram shows the place of ResultSet in the JDBC Framework. ResultSet can be obtained by executing SQL Query using Statement, PreparedStatement or CallableStatement.

上图显示了ResultSet在JDBC Framework中的位置。通过使用Statement ， PreparedStatement或CallableStatement执行SQL查询可以获得ResultSet 。

AutoCloseable, Wrapper are super interfaces of ResultSet. Now we will see how to work with ResultSet in our Java programs.

AutoCloseable ， Wrapper是ResultSet的超级接口。现在，我们将看到如何在Java程序中使用ResultSet。

ResultSet示例 (ResultSet Example)

We will be using MySQL for our example purpose. Use below DB script to create a database and table along with some records.

我们将使用MySQL作为示例。使用下面的DB脚本来创建数据库和表以及一些记录。


create database empdb;use empdb;create table tblemployee (empid integer primary key, firstname varchar(32), lastname varchar(32), dob date);insert into tblemployee values  (1, 'Mike', 'Davis',' 1998-11-11');
insert into tblemployee values  (2, 'Josh', 'Martin', '1988-10-22');
insert into tblemployee values  (3, 'Ricky', 'Smith', '1999-05-11');

Let’s have look at the below example program to fetch the records from the table and print them on the console. Please make sure you have the MySQL JDBC driver in the project classpath.

让我们看下面的示例程序，从表中获取记录并将其打印在控制台上。请确保在项目类路径中有MySQL JDBC驱动程序。


package com.journaldev.examples;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Date;/*** Java Resultset Example of Retrieving records.* * @author pankaj**/public class ResultSetDemo {public static void main(String[] args) {String query = "select empid, firstname, lastname, dob from tblemployee";Connection conn = null;Statement stmt = null;try {Class.forName("com.mysql.jdbc.Driver");conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/empdb", "root", "root");stmt = conn.createStatement();ResultSet rs = stmt.executeQuery(query);while (rs.next()) {Integer empId = rs.getInt(1);String firstName = rs.getString(2);String lastName = rs.getString(3);Date dob = rs.getDate(4);System.out.println("empId:" + empId);System.out.println("firstName:" + firstName);System.out.println("lastName:" + lastName);System.out.println("dob:" + dob);System.out.println("");}rs.close();} catch (Exception e) {e.printStackTrace();} finally {try {stmt.close();conn.close();} catch (Exception e) {}}}
}

Output:

输出：


empId:1
firstName:Mike
lastName:Davis
dob:1998-11-11empId:2
firstName:Josh
lastName:Martin
dob:1988-10-22empId:3
firstName:Ricky
lastName:Smith
dob:1999-05-11

Explanation:

说明：

ResultSet is obtained by calling the executeQuery method on Statement instance. Initially, the cursor of ResultSet points to the position before the first row.通过调用Statement实例上的executeQuery方法获得ResultSet。最初，ResultSet的光标指向第一行之前的位置。
The method next of ResultSet moves the cursor to the next row. It returns true if there is further row otherwise it returns false.ResultSet的next方法将光标移动到下一行。如果还有其他行，则返回true，否则返回false。
We can obtain data from ResultSet using getter methods provided by it. e.g. getInt(), getString(), getDate()我们可以使用它提供的getter方法从ResultSet中获取数据。例如getInt（），getString（），getDate（）
All the getter methods have two variants. 1^st variant takes column index as Parameter and 2^nd variant accepts column name as Parameter.所有的getter方法都有两个变体。 ^第一个变量将列索引作为参数， ^第二个变量将列名称作为参数。
Finally, we need to call close method on ResultSet instance so that all resources are cleaned up properly.最后，我们需要在ResultSet实例上调用close方法，以便正确清理所有资源。

结果集类型和并发 (ResultSet Types & Concurrency)

We can specify type and concurrency of ResultSet while creating an instance of Statement, PreparedStatement or CallableStatement.

在创建Statement， PreparedStatement或CallableStatement的实例时，我们可以指定ResultSet的类型和并发性。

statement.createStatement(int resultSetType, int resultSetConcurrency)

statement.createStatement（int resultSetType，int resultSetConcurrency）

结果集类型 (ResultSet Types)

1）仅转发（ResultSet。TYPE_FORWARD_ONLY ） (1) Forward Only (ResultSet.TYPE_FORWARD_ONLY))

This type of ResultSet instance can move only in the forward direction from the first row to the last row. ResultSet can be moved forward one row by calling the next() method. We can obtain this type of ResultSet while creating Instance of Statement, PreparedStatement or CallableStatement.

这种类型的ResultSet实例只能从第一行到最后一行向前移动。可以通过调用next（）方法将ResultSet向前移动一行。在创建Statement，PreparedStatement或CallableStatement的实例时，我们可以获取这种类型的ResultSet。


Statement stmt = connection.createStatement(ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_READ_ONLY);
ResultSet rs = stmt.executeQuery("select * from tbluser");

2）滚动不敏感（结果集。TYPE_SCROLL_INSENSITIVE） (2) Scroll Insensitive (ResultSet.TYPE_SCROLL_INSENSITIVE))

Scroll Insensitive ResultSet can scroll in both forward and backward directions. It can also be scrolled to an absolute position by calling the absolute() method. But it is not sensitive to data changes. It will only have data when the query was executed and ResultSet was obtained. It will not reflect the changes made to data after it was obtained.

滚动不敏感ResultSet可以向前和向后滚动。也可以通过调用absolute（）方法将其滚动到绝对位置。但是它对数据更改不敏感。它仅在执行查询并获得ResultSet时才具有数据。它不会反映获得数据后对数据所做的更改。


Statement stmt = connection.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,         ResultSet.CONCUR_READ_ONLY);
ResultSet rs = stmt.executeQuery("select * from tbluser");

3）敏感滚动（ResultSet。TYPE_SCROLL_SENSITIVE ） (3) Scroll Sensitive (ResultSet.TYPE_SCROLL_SENSITIVE))

Scroll Sensitive ResultSet can scroll in both forward and backward directions. It can also be scrolled to an absolute position by calling the absolute() method. But it is sensitive to data changes. It will reflect the changes made to data while it is open.

滚动敏感结果集可以向前和向后滚动。也可以通过调用absolute（）方法将其滚动到绝对位置。但是它对数据更改很敏感。它会反映打开时对数据所做的更改。


Statement stmt = connection.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,       ResultSet.CONCUR_READ_ONLY);
ResultSet rs = stmt.executeQuery("select * from tbluser");

ResultSet 并发 (ResultSet Concurrency)

1）只读（ResultSet。CONCUR_READ_ONLY ） (1) Read Only (ResultSet.CONCUR_READ_ONLY))

It is the default concurrency model. We can only perform Read-Only operations on ResultSet Instance. No update Operations are allowed.

它是默认的并发模型。我们只能对ResultSet实例执行只读操作。不允许任何更新操作。

2）可更新（ResultSet。CONCUR_UPDATABLE ） (2) Updatable (ResultSet.CONCUR_UPDATABLE))

In this case, we can perform update operations on ResultSet instance.

在这种情况下，我们可以对ResultSet实例执行更新操作。

结果集方法 (ResultSet Methods)

We can divide ResultSet methods into the following categories.

我们可以将ResultSet方法分为以下几类。

Navigational Methods导航方法
Getter/Reader Methods读/写方法
Setter/Updater Methods设置器/更新器方法
Miscellaneous Methods – close() and getMetaData()其他方法 – close（）和getMetaData（）

1. ResultSet导航方法 (1. ResultSet Navigational Methods)

boolean absolute(int row) throws SQLException: This method moves ResultSet cursor to the specified row and returns true if the operation is successful.boolean absolute（ int row）引发 SQLException ：此方法将ResultSet游标移动到指定的行，如果操作成功，则返回true。
void afterLast() throws SQLException: This method moves ResultSet cursor to the position after the last row.afterLast（）引发 SQLException 无效：此方法将ResultSet光标移动到最后一行之后的位置。
void beforeFirst() throws SQLException: This method moves ResultSet cursor to the position before the first row.void beforeFirst（）抛出 SQLException ：此方法将ResultSet光标移动到第一行之前的位置。
boolean first() throws SQLException: This method moves ResultSet cursor to the first row.boolean first（）引发 SQLException：此方法将ResultSet光标移到第一行。
boolean last() throws SQLException: This method moves ResultSet cursor to the last row.boolean last（）引发 SQLException：此方法将ResultSet光标移到最后一行。
boolean next() throws SQLException: This method moves ResultSet cursor to the next row.boolean next（）引发 SQLException：此方法将ResultSet光标移到下一行。
boolean previous() throws SQLException: This method moves ResultSet cursor to the previous row.boolean previous（）抛出 SQLException：此方法将ResultSet光标移到上一行。


package com.journaldev.examples;
import java.sql.*;/*** Java Resultset Example using navigational methods.* * @author pankaj**/
public class ResultSetDemo {public static void main(String[] args) {String query = "select empid, firstname, lastname, dob from tblemployee";Connection conn = null;Statement stmt = null;try {Class.forName("com.mysql.jdbc.Driver");conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/empdb", "root", "root");stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);ResultSet rs = stmt.executeQuery(query);System.out.println("All the rows of table=>");while (rs.next()) { // Go to next row by calling next() methoddisplayData(rs);}System.out.println("Now go directly to 2nd row=>");rs.absolute(2); // Go directly to 2nd rowdisplayData(rs);System.out.println("Now go to Previous row=>");rs.previous(); // Go to 1st row which is previous of 2nd rowdisplayData(rs);rs.close();} catch (Exception e) {e.printStackTrace();} finally {try {stmt.close();conn.close();} catch (Exception e) {}}}public static void displayData(ResultSet rs) throws SQLException {System.out.println("empId:" + rs.getInt(1));System.out.println("firstName:" + rs.getString(2));System.out.println("lastName:" + rs.getString(3));System.out.println("dob:" + rs.getDate(4));System.out.println("");}
}

Output:

输出：


All the rows of table=>
empId:1
firstName:Mike
lastName:Davis
dob:1998-11-11empId:2
firstName:Josh
lastName:Martin
dob:1988-10-22empId:3
firstName:Ricky
lastName:Smith
dob:1999-05-11Now go directly to 2nd row=>
empId:2
firstName:Josh
lastName:Martin
dob:1988-10-22Now go to Previous row=>
empId:1
firstName:Mike
lastName:Davis
dob:1998-11-11

2. ResultSet的Getter / Reader方法 (2. ResultSet Getter/Reader Methods)

int getInt(int columnIndex) throws SQLException: This method returns value of specified columnIndex as int.int getInt（ int columnIndex）引发 SQLException：此方法将指定columnIndex的值作为int返回。
long getLong(int columnIndex) throws SQLException: This method returns value of specified columnIndex as longlong getLong（ int columnIndex）抛出 SQLException：该方法返回指定columnIndex的值， 只要long
String getString(int columnIndex) throws SQLException: This method returns value of specified columnIndex as StringString getString（ int columnIndex）引发 SQLException：此方法将指定的columnIndex的值作为String返回
java.sql.Date getDate(int columnIndex) throws SQLException: This method returns value of specified columnIndex as java.sql.Datejava.sql.Date getDate（ int columnIndex）抛出 SQLException：此方法将指定columnIndex的值作为java.sql.Date返回
int getInt(String columnLabel) throws SQLException: This method returns value of specified column name as int.int getInt（String columnLabel）抛出 SQLException：此方法返回指定列名的值作为int 。
long getLong(String columnLabel) throws SQLException: This method returns value of specified column name as long.long getLong（String columnLabel）抛出 SQLException：此方法返回指定列名的值long 。
String getString(String columnLabel) throws SQLException: This method returns the value of the specified column name as String.String getString（String columnLabel）抛出 SQLException：此方法以String形式返回指定列名称的值。
java.sql.Date getDate(String columnLabel) throws SQLException: This method returns the value of the specified column name as java.sql.Date.java.sql.Date getDate（String columnLabel）引发SQLException：此方法以java.sql.Date的形式返回指定列名称的值。
ResultSet contains getter methods that return other primitive datatypes like boolean, float and double. It also has methods to obtain array and binary data from the database.ResultSet包含getter方法，这些方法返回其他原始数据类型，例如boolean，float和double。它还具有从数据库中获取数组和二进制数据的方法。

3. ResultSet 设置器/更新器方法 (3. ResultSet Setter/Updater Methods)

void updateInt(int columnIndex, int x) throws SQLException: This method updates the value of specified column of current row with int value.void updateInt（ int columnIndex， int x）引发 SQLException：此方法使用int值更新当前行的指定列的值。
void updateLong(int columnIndex, long x) throws SQLException: This method updates the value of the specified column of the current row with long value.void updateLong（ int columnIndex， long x）引发 SQLException：此方法使用long值更新当前行的指定列的值。
void updateString(int columnIndex, String x) throws SQLException: This method updates the value of the specified column of the current row with a String value.void updateString（int columnIndex，String x）引发SQLException：此方法使用String更新当前行的指定列的值值。
void updateDate(int columnIndex, java.sql.Date x) throws SQLException: This method updates the value of specified column of current row with java.sql.Date value.void updateDate（ int columnIndex，java.sql.Date x）引发 SQLException：此方法使用java.sql.Date更新当前行的指定列的值值。
void updateInt(String columnLabel, int x) throws SQLException: This method updates the value of the specified column label of the current row with int value.void updateInt（String columnLabel，int x）引发SQLException：此方法使用int值更新当前行的指定列标签的值。
void updateLong(String columnLabel, long x) throws SQLException: This method updates the value of the specified column label of the current row with long value.void updateLong（String columnLabel，long x）引发SQLException：此方法使用long值更新当前行的指定列标签的值。
void updateString(String columnLabel, String x) throws SQLException: This method updates the value of the specified column label of the current row with a String value.void updateString（String columnLabel，String x）引发SQLException：此方法使用String更新当前行的指定列标签的值值。
void updateDate(String columnLabel, java.sql.Date x) throws SQLException: This method updates the value of specified columnLabel of current row with java.sql.Date value.void updateDate（String columnLabel，java.sql.Date x）引发 SQLException：此方法使用java.sql.Date值更新当前行的指定columnLabel的值。

Note: Setter/Updater Methods doesn’t directly update database values. Database values will be inserted/updated after calling the insertRow or updateRow method.

注意：设置器/更新器方法不会直接更新数据库值。 调用insertRow或updateRow方法后，将插入/更新数据库值 。


package com.journaldev.examples;
import java.sql.*;/*** Java Resultset Example using updater methods.* * @author pankaj**/public class ResultSetUpdateDemo {public static void main(String[] args) {String query = "select empid, firstname, lastname, dob from tblemployee";Connection conn = null;Statement stmt = null;try {Class.forName("com.mysql.jdbc.Driver");conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/empdb", "root", "root");stmt = conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_UPDATABLE);ResultSet rs = stmt.executeQuery(query);System.out.println("Now go directly to 2nd row for Update");if (rs.absolute(2)) { // Go directly to 2nd rowSystem.out.println("Existing Name:" + rs.getString("firstName"));rs.updateString("firstname", "Tyson");rs.updateRow();}rs.beforeFirst(); // go to startSystem.out.println("All the rows of table=>");while (rs.next()) { // Go to next row by calling next() methoddisplayData(rs);}rs.close();} catch (Exception e) {e.printStackTrace();} finally {try {stmt.close();conn.close();} catch (Exception e) {}}}public static void displayData(ResultSet rs) throws SQLException {System.out.println("empId:" + rs.getInt(1));System.out.println("firstName:" + rs.getString(2));System.out.println("lastName:" + rs.getString(3));System.out.println("dob:" + rs.getDate(4));System.out.println("");}
}

Output:

输出：


Now go directly to 2nd row for Update
Existing Name:Josh
All the rows of table=>
empId:1
firstName:Mike
lastName:Davis
dob:1998-11-11empId:2
firstName:Tyson
lastName:Martin
dob:1988-10-22empId:3
firstName:Ricky
lastName:Smith
dob:1999-05-11

4. ResultSet其他方法 (4. ResultSet Miscellaneous Methods)

void close() throws SQLException: This method frees up resources associated with ResultSet Instance. It must be called otherwise it will result in resource leakage.void close（）抛出 SQLException ：此方法释放与ResultSet实例关联的资源。必须调用它，否则将导致资源泄漏。
ResultSetMetaData getMetaData() throws SQLException: This method returns ResultSetMetaData instance. It gives information about the type and property of columns of the query output.ResultSetMetaData getMetaData（）引发 SQLException：此方法返回ResultSetMetaData实例。它提供有关查询输出的列的类型和属性的信息。

Reference: Java doc

参考： Java文档

翻译自: https://www.journaldev.com/34720/java-resultset