Beispiel für eine JDBC-Transaktion

JDBC-Transaktion stellt sicher, dass eine Reihe von SQL-Anweisungen als Einheit ausgeführt wird, entweder alle Anweisungen erfolgreich ausgeführt werden oder KEINE der Anweisungen ausgeführt wird (alle Änderungen rückgängig gemacht).

1. Ohne JDBC-Transaktion

1.1 A JDBC example to insert two rows and update one row.

TransactionExample.java

package com.example.jdbc;

import java.math.BigDecimal;
import java.sql.*;
import java.time.LocalDateTime;

public class TransactionExample {

    public static void main(String[] args) {

        try (Connection conn = DriverManager.getConnection(
                "jdbc:postgresql://127.0.0.1:5432/test", "postgres", "password");
             Statement statement = conn.createStatement();
             PreparedStatement psInsert = conn.prepareStatement(SQL_INSERT);
             PreparedStatement psUpdate = conn.prepareStatement(SQL_UPDATE)) {

            statement.execute(SQL_TABLE_DROP);
            statement.execute(SQL_TABLE_CREATE);

            // Run list of insert commands
            psInsert.setString(1, "example");
            psInsert.setBigDecimal(2, new BigDecimal(10));
            psInsert.setTimestamp(3, Timestamp.valueOf(LocalDateTime.now()));
            psInsert.execute();

            psInsert.setString(1, "kungfu");
            psInsert.setBigDecimal(2, new BigDecimal(20));
            psInsert.setTimestamp(3, Timestamp.valueOf(LocalDateTime.now()));
            psInsert.execute();

            // Run list of update commands

            // below line caused error, test transaction
            // org.postgresql.util.PSQLException: No value specified for parameter 1.
            psUpdate.setBigDecimal(2, new BigDecimal(999.99));

            //psUpdate.setBigDecimal(1, new BigDecimal(999.99));
            psUpdate.setString(2, "example");
            psUpdate.execute();

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    private static final String SQL_INSERT = "INSERT INTO EMPLOYEE (NAME, SALARY, CREATED_DATE) VALUES (?,?,?)";

    private static final String SQL_UPDATE = "UPDATE EMPLOYEE SET SALARY=? WHERE NAME=?";

    private static final String SQL_TABLE_CREATE = "CREATE TABLE EMPLOYEE"
            + "("
            + " ID serial,"
            + " NAME varchar(100) NOT NULL,"
            + " SALARY numeric(15, 2) NOT NULL,"
            + " CREATED_DATE timestamp with time zone NOT NULL DEFAULT CURRENT_TIMESTAMP,"
            + " PRIMARY KEY (ID)"
            + ")";

    private static final String SQL_TABLE_DROP = "DROP TABLE EMPLOYEE";

}

Ausgabe, das Update ist fehlgeschlagen und eine Ausnahme wird ausgelöst. Am Ende werden 2 Zeilen eingefügt, aber das Update wird übersprungen.

org.postgresql.util.PSQLException: No value specified for parameter 1.
    at org.postgresql.core.v3.SimpleParameterList.checkAllParametersSet(SimpleParameterList.java:257)
    at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:292)
    at org.postgresql.jdbc.PgStatement.executeInternal(PgStatement.java:441)
    at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:365)
    at org.postgresql.jdbc.PgPreparedStatement.executeWithFlags(PgPreparedStatement.java:143)
    at org.postgresql.jdbc.PgPreparedStatement.execute(PgPreparedStatement.java:132)
    at com.example.jdbc.TransactionExample.main(TransactionExample.java:41)

output

2. Verwenden der JDBC-Transaktion

2.1 To enable transaction, set auto commit to false.

conn.setAutoCommit(false); // default true
// start transaction block

// insert
// update
// if any errors within the start and end block,
// rolled back all changes, none of the statements are executed.

// end transaction block
conn.commit();

2.2 Same example with JDBC transaction.

TransactionExample.java

package com.example.jdbc;

import java.math.BigDecimal;
import java.sql.*;
import java.time.LocalDateTime;

public class TransactionExample {

    public static void main(String[] args) {

        try (Connection conn = DriverManager.getConnection(
                "jdbc:postgresql://127.0.0.1:5432/test", "postgres", "password");
             Statement statement = conn.createStatement();
             PreparedStatement psInsert = conn.prepareStatement(SQL_INSERT);
             PreparedStatement psUpdate = conn.prepareStatement(SQL_UPDATE)) {

            statement.execute(SQL_TABLE_DROP);
            statement.execute(SQL_TABLE_CREATE);

            // start transaction block
            conn.setAutoCommit(false); // default true

            // Run list of insert commands
            psInsert.setString(1, "example");
            psInsert.setBigDecimal(2, new BigDecimal(10));
            psInsert.setTimestamp(3, Timestamp.valueOf(LocalDateTime.now()));
            psInsert.execute();

            psInsert.setString(1, "kungfu");
            psInsert.setBigDecimal(2, new BigDecimal(20));
            psInsert.setTimestamp(3, Timestamp.valueOf(LocalDateTime.now()));
            psInsert.execute();

            // Run list of update commands

            // error, test roolback
            // org.postgresql.util.PSQLException: No value specified for parameter 1.
            psUpdate.setBigDecimal(2, new BigDecimal(999.99));
            //psUpdate.setBigDecimal(1, new BigDecimal(999.99));
            psUpdate.setString(2, "example");
            psUpdate.execute();

            // end transaction block, commit changes
            conn.commit();

            // good practice to set it back to default true
            conn.setAutoCommit(true);

        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    //...

}

Ausgabe, keine der Anweisungen wird ausgeführt, die Einfügeanweisungen werden zurückgesetzt.

org.postgresql.util.PSQLException: No value specified for parameter 1.
    at org.postgresql.core.v3.SimpleParameterList.checkAllParametersSet(SimpleParameterList.java:257)
    at org.postgresql.core.v3.QueryExecutorImpl.execute(QueryExecutorImpl.java:292)
    at org.postgresql.jdbc.PgStatement.executeInternal(PgStatement.java:441)
    at org.postgresql.jdbc.PgStatement.execute(PgStatement.java:365)
    at org.postgresql.jdbc.PgPreparedStatement.executeWithFlags(PgPreparedStatement.java:143)
    at org.postgresql.jdbc.PgPreparedStatement.execute(PgPreparedStatement.java:132)
    at com.example.jdbc.TransactionExample.main(TransactionExample.java:41)

output

3. Extra…

Beheben Sie den Fehlerparameter 1und sehen Sie das erwartete Ergebnis.

    //psUpdate.setBigDecimal(2, new BigDecimal(999.99));

    psUpdate.setBigDecimal(1, new BigDecimal(999.99));
    psUpdate.setString(2, "example");
    psUpdate.execute();

Ausgabe

2 rows are inserted and 1 row is updated.

output

Quellcode herunterladen

$ git clone https://github.com/example/java-jdbc.git
$ cd postgresql

TOC

Beispiel für eine JDBC-Transaktion